Copyright © 2001, 2002, 2003 Christopher B. Powell
Copyright © 2004, 2005 Edward Rudd
| Revision History | |
|---|---|
| Revision 1.3 | 2005-01-11 |
| Updated for mod_log_sql v1.100 | |
| Revision 1.2 | 2004-04-08 |
| Updated for mod_log_sql v1.97 | |
| Revision 1.1 | 2004-03-02 |
| Updated for mod_log_sql v1.96 | |
| Revision 1.0 | 2004-01-22 |
| Initial Conversion from Lyx to Docbook | |
Table of Contents
This Apache module will permit you to log to a SQL database; it can log each access request as well as data associated with each request: cookies, notes, and inbound/outbound headers. Unlike logging to a flat text file -- which is standard in Apache -- a SQL-based log exhibits tremendous flexibility and power of data extraction. (See FAQ entry Q: 1.1. for further discussion and examples of the advantages to SQL.)
This module can either replace or happily coexist with mod_log_config, Apache's text file logging facility. In addition to being more configurable than the standard module, mod_log_sql is much more flexible.
This project was formerly known as "mod_log_mysql." It was renamed "mod_log_sql" in order to reflect the project goal of database in-specificity. The module currently supports MySQL, but support for other database back-ends is underway.
In order to save speed and overhead, links are kept alive in between queries. This module uses one dedicated SQL link per httpd child, opened by each child process when it is born. Among other things, this means that this module supports logging into only one MySQL server, and for now, also, only one SQL database. But that's a small tradeoff compared to the blinding speed of this module. Error reporting is robust throughout the module and will inform the administrator of database issues in the Apache ErrorLog for the server/virtual server.
Virtual hosts are supported in the same manner they are in the regular logging modules. The administrator defines some basic 'global' directives in the main server config, then defines more specific 'local' directives inside each VirtualHost stanza.
A robust "preserve" capability has now been implemented. This permits the module to preserve any failed INSERT commands to a local file on its machine. In any situation that the database is unavailable -- e.g. the network fails or the database host is rebooted -- mod_log_sql will note this in the error log and begin appending its log entries to the preserve file (which is created with the user and group ID of the running Apache process, e.g. "nobody/nobody" on many Linux installations). When database availability returns, mod_log_sql seamlessly resumes logging to it. When convenient for the sysadmin, he/she can easily import the preserve file into the database because it is simply a series of SQL insert statements.
All the data that would be contained in the "Combined Log Format" is logged by default, plus a little extra. Your best bet is to begin by accepting this default, then later customize the log configuration based on your needs. The documentation of the run-time directives includes a full explanation of what you can log, including examples -- see section Configuration Directive Reference.
Note which directives go in the 'main server config' and which directives apply to the 'virtual host config'. This is made clear in the directive documentation.
The 'time_stamp' field is stored in an UNSIGNED INTEGER format, in the standard unix "seconds since the epoch" format. This is superior to storing the access time as a string due to size requirements: an UNSIGNED INT requires 4 bytes, whereas an Apache date string (e.g. "18/Nov/2001:13:59:52 -0800") requires 26 bytes: those extra 22 bytes become significant when multiplied by thousands of accesses on a busy server. Besides, an INT type is far more flexible for comparisons, etc.
In MySQL 3.21 and above you can easily convert this to a human readable format using from_unixtime(), e.g.:
select remote_host,request_uri,from_unixtime(time_stamp) from access_log;
The enclosed perl program "make_combined_log.pl" extracts your access log in a format that is completely compatible with the Combined Log Format. You can then feed this to your favorite web log analysis tool.
The table's string values can be CHAR or VARCHAR, at a length of your choice. VARCHAR is superior because it truncates long strings; CHAR types are fixed-length and will be padded with spaces, resulting in waste. Just like the time_stamp issue described above, that kind of space waste multiplies over thousands of records.
Be careful not to go overboard setting fields to NOT NULL. If a field is marked NOT NULL then it must contain data in the INSERT statement, or the INSERT will fail. These mysterious failures can be quite frustrating and difficult to debug.
When Apache logs a numeric field, it uses a '-' character to mean "not applicable," e.g. the number of bytes returned on a 304 (unchanged) request. Since '-' is an illegal character in an SQL numeric field, such fields are assigned the value 0 instead of '-' which, of course, makes perfect sense anyway.
The actual logging code was taken from the already existing flat file text modules, so all that credit goes to the Apache Software Foundation.
The MySQL routines and directives were added by Zeev Suraski <bourbon@netvision.net.il>.
All changes from 1.06+ and the new documentation were added by Chris Powell <chris <at> grubbybaby <dot> com>. It seems that the module had fallen into the "un-maintained" category -- it had not been updated since 1998 -- so Chris adopted it as the new maintainer.
In December of 2003, Edward Rudd <urkle <at> outoforder <dot> cc> porting the module to Apache 2.0, cleaning up the code, converting the documentation to DocBook, optimizing the main logging loop, and added the much anticipated database abstraction layer.
As of February 2004, Chris Powell handed over maintenance of the module over to Edward Rudd. So you should contact Edward Rudd about the module from now on.
A general discussion and support mailing list is provided for mod_log_sq at lists.outoforder.cc. To subscribe to the mailing list send a blank e-mail to mod_log_sql-subscribe@lists.outoforder.cc. The list archives can be accessed via Gmane.org's mailng list gateway via any new reader news://news.gmane.org/gmane.comp.apache.mod-log-sql, or via a web browser at http://news.gmane.org/gmane.comp.apache.mod-log-sql.
A compatible system. mod_log_sql was authored and tested on systems based on Red Hat Linux (Red Hat, Mandrake), but the module should easily adapt to any modern distribution. mod_log_sql has also been ported successfully to Solaris and FreeBSD.
Apache 1.3 or 2.0, 1.2 is no longer supported, but may still compile. Ideally you should already have successfully compiled Apache and understand the process, but this document tries to make it simple for beginners.
The MySQL development headers. This package is called different things on different distributions. For example, Red Hat 6.x calls this RPM "MySQL-devel" whereas Mandrake calls it "libmysql10-devel." Both MySQL 3.23.x and 4.x are supported.
MySQL >= 3.23.15 configured, installed and running on either localhost or an accessible networked machine. You should already have a basic understanding of MySQL and how it functions.
Optionally, if you want to be able to log SSL information such as keysize or cipher, you need OpenSSL and mod_ssl installed.
Unpack the archive into a working directory.
$ tar -xzf mod_log_sql-1.94.tar.gz $ cd mod_log_sql-1.9
run configure to configure the source directory.
$ ./configure
The configure script should automatically detect all the required libraries and program if the are installed in standard locations.. If it returns an error, here is a description of the arguments you can specify when you run configure.
This is the full path to the apxs binary, or the directory which contains the program. This program is part of the Apache 1.3 and 2.0 installation.
The default is to search /usr/bin/apxs and /usr/sbin/apxs.
Specifying a directory here will search $directory/apxs, $directory/bin/apxs, and $directory/sbin/apxs
If you have more than one version of Apache installed, you need to specify the correct apxs binary for the one you wish to compile for.
This is the directory to search for the libmysqlclient library and the MySQL headers.
The default is to search /usr/include, /usr/include/mysql, /usr/local/include, and /usr/local/include/mysql for MySQL headers.. And /usr/lib. /usr/lib/mysql, /usr/local/lib, and /usr/local/lin/mysql for the MySQL libraries.
Specifying this testargument will search $directory/include and $directory/mysql for MySQL headers. And $directory/lib and $directory/lib/mysql for MySQL libraries.
Specifying this argument will enable the search for mod_ssl and SSL headers, and if found will enable compilation of SSL support into mod_log_sql. SSL support is compiled into a separate module that can be loaded after the main mod_log_sql.
This is the path to the SSL toolkit header files that were used to compile mod_ssl. If you want SSL support you most likely need to specify this.
The default is to search /usr/include and /usr/include/openssl.
Specifying this argument will search that directory for the SSL headers.
This argument is only needed when compiling SSL support for Apache 1.3, and needs to be the directory which contains the ndbm.h header file. You can find this by using
$ locate ndbm.h /usr/include/db1/ndbm.h /usr/include/gdbm/ndbm.h
As far as I can tell, there is no difference as to which you specify, but it should be the one that you compiled mod_ssl with.
The default is /usr/include/db1, which should work on most systems.
This will disable the apache version test. However there is a side affect if you specify this where I will not be able to determine which version of Apache you are compiling for. So don't specify this.. If you are having troubles with the script detecting your Apache version, then send a bug report along with your system OS version and versions of related packages.
This will disable the MySQL compile test. Specify this if for some reason the test fail but you know you have specified the correct directories. If mod_los_sql also fails to compile report a bug along with your system OS version and versions of related packages.
Now compile the module with GNU make. You may have to specify gmake on some systems like FreeBSD.
$ gmake
If there were no errors, you can now install the module(s). If you compiled as a non-root user you may need to switch users with su or sudo.
$ su -c "gmake install" Password:
Now edit your Apache configuration and load the modules.
If you are loading the SSL logging module, you need to make sure it is loaded after mod_ssl and mod_log_sql.
If you have previously used mod_log_sql version 1.18, the name of the module has changed from sql_log_module to log_sql_module (the first parameter to LoadModule)
If you are upgrading from any release earlier than 1.97 you need to add an extra LoadModule directive to load the database driver (ie mysql).
Insert these lines to either the main httpd.conf or a file included via an include directive.
LoadModule log_sql_module modules/mod_log_sql.so LoadModule log_sql_mysql_module modules/mod_log_sql_mysql.so <IfModule mod_ssl.c> LoadModule log_sql_ssl_module moduels/mod_log_sql_ssl.so </IfModule>
If you did not compile SSL support in mod_log_sql, do not include the lines between the <IfModule> directives.
If you are using Apache 1.3 you may need add these lines later in the configuration.
AddModule mod_log_sql.c AddModule mod_log_sql_mysql.c <IfModule mod_ssl.c> AddModule mod_log_sql_ssl.c </IfModule>
If you did not compile SSL support in mod_log_sql, do not include the lines between the <IfModule> directives.
You have to prepare the database to receive data from mod_log_sql, and set up run-time directives in httpd.conf to control how and what mod_log_sql logs.
This section will discuss how to get started with a basic configuration. Full documentation of all available run-time directives is available in section Configuration Directive Reference.
mod_log_sql can make its own tables on-the-fly, or you can pre-make the tables by hand. The advantage of letting the module make the tables is ease-of-use, but for raw performance you will want to pre-make the tables in order to save some overhead. In this basic setup we'll just let the module create tables for us.
We still need to have a logging database created and ready, so run the MySQL command line client and create a database:
# mysql -uadmin -pmypassword Enter password: mysql> create database apachelogs;
If you want to hand-create the tables, run the enclosed 'create-tables' SQL script as follows ("create_tables.sql" needs to be in your current working directory).
mysql> use apachelogs Database changed mysql> source create_tables.sql
Create a specific MySQL userid that httpd will use to authenticate and enter data. This userid need not be an actual Unix user. It is a userid internal to MySQL with specific privileges. In the following example command, "apachelogs" is the database, "loguser" is the userid to create, "my.apachemachine.com" is the name of the Apache machine, and "l0gger" is the password to assign. Choose values that are different from these examples.
mysql> grant insert,create on apachelogs.* to loguser@my.apachemachine.com identified by 'l0gger';
You may be especially security-paranoid and want "loguser" to not have "create" capability within the "apachelogs" database. You can disable that privilege, but the cost is that you will not be able to use the module's on-the-fly table creation feature. If that cost is acceptable, hand-create the tables as described in step 3 and use the following GRANT statement instead of the one above:
mysql> grant insert on apachelogs.* to loguser@my.apachemachine.com identified by 'l0gger';
Enable full logging of your MySQL daemon (at least temporarily for debugging purposes) if you don't do this already. Edit /etc/my.cnf and add the following line to your [mysqld] section:
log=/var/log/mysql-messages
Then restart MySQL
# /etc/rc.d/init.d/mysql restart
Tell the module what database to use and the appropriate authentication information.
So, edit httpd.conf and insert the following lines somewhere after any LoadModule / AddModule statements. Make sure these statements are "global," i.e. not inside any VirtualHost stanza. You will also note that you are embedding a password in the file. Therefore you are advised to "chmod 660 httpd.conf" to prevent unauthorized regular users from viewing your database user and password.
Use the MySQL database called "apachelogs" running on "dbmachine.foo.com". Use username "loguser" and password "l0gg3r" to authenticate to the database. Permit the module create tables for us.
Example 1. Basic Example
LogSQLLoginInfo mysql://loguser:l0gg3r@dbmachine.foo.com/apachelogs LogSQLCreateTables on
If your database resides on localhost instead of another host, specify the MySQL server's socket file as follows:
LogSQLDBParam socketfile /your/path/to/mysql.sock
If your database is listening on a port other than 3306, specify the correct TCP port as follows:
LogSQLDBParam port 1234
The actual logging is set up on a virtual-host-by-host basis. So, skip down to the virtual host you want to set up. Instruct this virtual host to log entries to the table "access_log" by inserting a LogSQLTransferLogTable directive. (The LogSQLTransferLogTable directive is the minimum required to log -- other directives that you will learn about later simply tune the module's behavior.)
<VirtualHost 1.2.3.4> [snip] LogSQLTransferLogTable access_log [snip] </VirtualHost>
Restart apache.
# /etc/rc.d/init.d/httpd stop # /etc/rc.d/init.d/httpd start
Visit your web site in a browser to trigger some hits, then confirm that the entries are being successfully logged:
# mysql -hdbmachine.foo.com -umysqladmin -p -e "select * from access_log" apachelogs Enter password:
Several lines of output should follow, corresponding to your hits on the site. You now have basic functionality. Don't disable your regular Apache logs until you feel comfortable that the database is behaving as you'd like and that things are going well. If you do not see any entries in the access_log, please consult section Q: 2.2. of the FAQ on how to debug and fix the situation.
You can now activate the advanced features of mod_log_sql, which are described in the next section.
The most basic directive for the module is LogSQLTransferLogFormat, which tells the module which information to send to the database; logging to the database will not take place without it. Place a LogSQLTransferLogFormat directive in the VirtualHost stanza of each virtual host that you want to activate.
After LogSQLTransferLogFormat you supply a string of characters that tell the module what information to log. In the configuration directive reference (section LogSQLTransferLogFormat ) there is a table which clearly defines all the possible things to log. Let's say you want to log only the "request time," the "remote host," and the "request"; you'd use:
LogSQLTransferLogFormat hUS
But a more appropriate string to use is
LogSQLTransferLogFormat AbHhmRSsTUuv
which logs all the information required to be compatible with the Combined Log Format (CLF).
If you don't choose to log everything that is available, that's fine. Fields in the unused columns in your table will simply contain NULL.
Some of the LogSQLTransferLogFormat characters require a little extra configuration:
If you specify 'c' to indicate that you want to log the cookie value, you must also tell the module which cookie you mean by using LogSQLWhichCookie -- after all, there could be many cookies associated with a given request. Fail to specify LogSQLWhichCookie, and no cookie information at all will be logged.
If you specify 'M' to indicate that you want to log the machine ID, you must also tell the module this machine's identity using the LogSQLMachineID directive. Fail to specify LogSQLMachineID, and a simple '-' character will be logged in the machine_id column.
One "accept" and two "ignore" directives allow you to fine-tune what the module should not log. These are very handy for keeping your database as uncluttered as possible and keeping your statistics free of unneeded numbers. Think of each one as a gatekeeper.
It is important to remember that each of these three directives is purely optional. mod_log_sql's default is to log everything.
When a request comes in, the contents of LogSQLRequestAccept are evaluated first. This optional, "blanket" directive lets you specify that only certain things are to be accepted for logging, and everything else discarded. Because it is evaluated before LogSQLRequestIgnore and LogSQLRemhostIgnore it can halt logging before those two filtering directives "get their chance."
Once a request makes it past LogSQLRequestAccept, it still can be excluded based on LogSQLRemhostIgnore and LogSQLRequestIgnore. A good way to use LogSQLRemhostIgnore is to prevent the module from logging the traffic that your internal hosts generate. LogSQLRequestIgnore is great for preventing things like requests for "favicon.ico" from cluttering up your database, as well as excluding the various requests that worms make, etc.
You can specify a series of strings after each directive. Do not use any type of globbing or regular-expression syntax -- each string is considered a match if it is a substring of the larger request or remote-host; the comarison is case-sensitive. This means that "LogSQLRemhostIgnore micro" will ignore requests from "microsoft.com," "microworld.net," "mymicroscope.org," etc. "LogSQLRequestIgnore gif" will instruct the module to ignore requests for "leftbar.gif," "bluedot.gif" and even "giftwrap.jpg" -- but "RED.GIF" and "Tree.Gif" would still get logged because of case sensitivity.
A summary of the decision flow:
If LogSQLRequestAccept exists and a request does not match anything in that list, it is discarded.
If a request matches anything in the LogSQLRequestIgnore list, it is discarded.
If a reqiest matches anything in the LogSQLRemhostIgnore list, it is discarded.
Otherwise the request is logged.
This means that you can have a series of directives similar to the following:
LogSQLRequestAccept .html .gif .jpg LogSQLRequestIgnore statistics.html bluedot.jpg
So the first line instructs the module to only log files with html, gif and jpg suffixes; requests for "formail.cgi" and "shopping-cart.pl" will never be considered for logging. ("LeftArrow.JPG" will also never be considered for logging -- remember, the comparison is case sensitive.) The second line prunes the list further -- you never want to log requests for those two objects.
If you want to match all the hosts in your domain such as "host1.corp.foo.com" and "server.dmz.foo.com", simply specify:
LogSQLRemhostIgnore foo.com
A great way to catch the vast majority of worm-attack requests and prevent them from being logged is to specify:
LogSQLRequestIgnore root.exe cmd.exe default.ida
To prevent the logging of requests for common graphic types, make sure to put a '.' before the suffix to avoid matches that you didn't intend:
LogSQLRequestIgnore .gif .jpg
mod_log_sql has three basic tiers of operation:
The administrator creates all necessary tables by hand and configures each Apache VirtualHost by hand. (LogSQLCreateTables Off)
The module is permitted to create necessary tables on-the-fly, but the administrator configures each Apache VirtualHost by hand. (LogSQLCreateTables On)
The module is permitted to create all necessary tables and to make intelligent, on-the-fly configuration of each VirtualHost. (LogSQLMassVirtualHosting On)
Many users are happy to use the module in its most minimal form: they hand-create any necessary tables (using "create_tables.sql"), and they configure each VirtualHost by hand to suit their needs. However, some administrators need extra features due to a large and growing number of VirtualHosts. The LogSQLMassVirtualHosting directive activates module capabilities that make it far easier to manage an ISP environment, or any situation characterized by a large and varying number of virtual servers.
the on-the-fly table creation feature is activated automatically
the transfer log table name is dynamically set from the virtual host's name (example: a virtual host "www.grubbybaby.com" gets logged to table "access_www_grubbybaby_com")
There are numerous benefits. The admin will not need to create new tables for every new VirtualHost. (Although the admin will still need to drop the tables of virtual hosts that are removed.) The admin will not need to set LogSQLTransferLogTable for each virtual host -- it will be configured automatically based on the host's name. Because each virtual host will log to its own segregated table, data about one virtual server will segregate from others; an admin can grant users access to the tables they need, and they will be unable to view data about another user's virtual host.
In an ISP scenario the admin is likely to have a cluster of many front-end webservers logging to a back-end database. mod_log_sql has a feature that permits analysis of how well the web servers are loadbalancing: the LogSQLMachineID directive. The administrator uses this directive to assign a unique identifier to each machine in the web cluster, e.g. "LogSQLMachineID web01," "LogSQLMachineID web02," etc. Used in conjunction with the 'M' character in LogSQLTransferLogFormat, each entry in the SQL log will include the machine ID of the machine that created the entry. This permits the administrator to count the entries made by each particular machine and thereby analyze the front-end loadbalancing algorithm.
A given HTTP request can have a one-to-many relationship with certain kinds of data. For example, a single HTTP request can have 4 cookies, 3 headers and 5 "mod_gzip" notes associated with it. mod_log_sql is capable of logging these relationships due to the elegance of SQL relational data.
You already have a single table containing access requests. One of the columns in that table is 'id' which is intended to contain the unique request ID supplied by the standard Apache module mod_unique_id -- all you need to do is compile in that module and employ the LogSQLTransferLogFormat character 'I'. Thereafter, each request gets a unique ID that can be thought of as a primary key within the database, useful for joining multiple tables. So let's envision several new tables: a notes table, a cookies table, and a table for inbound and outbound headers.
Table 1. <tblAcc>access_log
| id | remote_host | request_uri | time_stamp | status | bytes_sent |
|---|---|---|---|---|---|
| PPIDskBRH30AAGPtAsg | zerberus.aiacs.net | /mod_log_sql/index.html | 1022493617 | 200 | 2215 |
Table 2. <tblNotes>notes_log
| id | item | val |
|---|---|---|
| PPIDskBRH30AAGPtAsg | mod_gzip_result | OK |
| PPIDskBRH30AAGPtAsg | mod_gzip_compression_ratio | 69 |
Table 3. <tblHdr>headers_log
| id | item | val |
|---|---|---|
| PPIDskBRH30AAGPtAsg | Content-Type | text/html |
| PPIDskBRH30AAGPtAsg | Accept-Encoding | gzip, deflate |
| PPIDskBRH30AAGPtAsg | Expires | Tue, 28 May 2002 10:00:18 GMT |
| PPIDskBRH30AAGPtAsg | Cache-Control | max-age=86400 |
We have a certain request, and its unique ID is "PPIDskBRH30AAGPtAsg". Within each separate table will be multiple entries with that request ID: several cookie entries, several header entries, etc. As you can see in tables [tblAcc], [tblNotes] and [tblHdr], you have a one-to-many relationship for request PPIDskBRH30AAGPtAsg: that one access has two associated notes and four associated headers. You can extract this data easily using the power of SQL's "select" statement and table joins. To see the notes associated with a particular request:
select a.remote_host, a.request_uri, n.item, n.val from access_log a, notes_log n where a.id=n.id and a.id='PPIDskBRH30AAGPtAsg';
Table 4. access_log joined to notes_log
| remote_host | request_uri | item | val |
|---|---|---|---|
| zerberus.aiacs.net | /mod_log_sql/index.html | mod_gzip_result | OK |
| zerberus.aiacs.net | /mod_log_sql/index.html | mod_gzip_compression_ratio | 69 |
Naturally you can craft similar statements for the outboud headers, inbound headers and cookies, all of which can live in separate tables. Your statements are limited in power only by your skill with SQL.
In order to use this capability of mod_log_sql, you must do several things.
Compile mod_unique_id into Apache (statically or as a DSO). mod_log_sql employs the unique request ID that mod_unique_id provides in order to key between the separate tables. You can still log the data without mod_unqiue_id, but it will be completely uncorrelated and you will have no way to discern any meaning.
Create the appropriate tables. This will be done for you if you permit mod_log_sql to create its own tables using LogSQLCreateTables On, or if you use the enclosed "create_tables.sql" script.
Create a SQL index on the "id" column. Without this index, table joins will be deathly slow. I recommend you consult the MySQL documentation on the proper way to create a column index if you are not familiar with this operation.
Within each appropriate VirtualHost stanza, use the LogSQLWhich* and LogSQL*LogTable directives to tell the module what and where to log the data. In the following example, I have overridden the name for the notes table whereas I have left the other table names at their defaults. I have then specified the cookies, headers and notes that interest me. (And as you can see, these directives do not require me to add any characters to LogSQLTransferLogTable.)
<VirtualHost 216.231.36.128> (snip) LogSQLNotesLogTable notestable LogSQLWhichCookies bluecookie redcookie greencookie LogSQLWhichNotes mod_gzip_result mod_gzip_compression_ratio LogSQLWhichHeadersOut Expires Content-Type Cache-Control LogSQLWhichHeadersIn UserAgent Accept-Encoding Host (snip) </VirtualHost>
Although sub-optimal, it is not uncommon to use the same back-end database for the "production" webservers as well as the "test" webservers (budgetary constraints, rack-space limits, etc.). Furthermore, an administrator in this situation may be unable to use LogSQLRemhostIgnore to exclude requests from the test servers -- perhaps the generated entries are genuinely useful for analytical or QA purposes, but their value after analysis is minimal.
It is wasteful and potentially confusing to permit this internal test data to clutter the database, and a solution to the problem is the proper use of the LogSQLMachineID directive. Assume a scenario where the production webservers have IDs like "web01," "web02," and so on -- and the test webservers have IDs like "test01," "test02," etc. Because entries in the log database are distinguished by their source machine, an administrator may purge unneeded test data from the access log as follows:
delete from access_log where machine_id like 'test%';
A busy MySQL database will have SELECT statements running concurrently with INSERT and UPDATE statements. A long-running SELECT can in certain circumstances block INSERTs and therefore block mod_log_sql. A workaround is to enable mod_log_sql for "delayed inserts," which are described as follows in the MySQL documentation.
The DELAYED option for the INSERT statement is a MySQL-specific option that is very useful if you have clients that can't wait for the INSERT to complete. This is a common problem when you use MySQL for logging and you also periodically run SELECT and UPDATE statements that take a long time to complete. DELAYED was introduced in MySQL Version 3.22.15. It is a MySQL extension to ANSI SQL92.
INSERT DELAYED only works with ISAM and MyISAM tables. Note that as MyISAM tables supports concurrent SELECT and INSERT, if there is no free blocks in the middle of the data file, you very seldom need to use INSERT DELAYED with MyISAM.
When you use INSERT DELAYED, the client will get an OK at once and the row will be inserted when the table is not in use by any other thread.
Another major benefit of using INSERT DELAYED is that inserts from many clients are bundled together and written in one block. This is much faster than doing many separate inserts.
The general disadvantages of delayed inserts are
The queued rows are only stored in memory until they are inserted into the table. If mysqld dies unexpectedly, any queued rows that were not written to disk are lost.
There is additional overhead for the server to handle a separate thread for each table on which you use INSERT DELAYED.
The MySQL documentation concludes, "This means that you should only use INSERT DELAYED when you are really sure you need it!" Furthermore, the current state of error return from a failed INSERT DELAYED seems to be in flux, and may behave in unpredictable ways between different MySQL versions. See FAQ entry Q: 3.4. -- you have been warned.
If you are experiencing issues which could be solved by delayed inserts, then set LogSqlDelayedInserts On in the httpd.conf. All regular INSERT statements are now INSERT DELAYED, and you should see no more blocking of the module.
It is imperative that you understand which directives are used only once in the main server config, and which are used inside VirtualHost stanzas and therefore multiple times within httpd.conf. The "context" listed with each entry informs you of this.
LogSQLLoginInfo {connection URI}
Example: LogSQLLoginInfo mysql://logwriter:passw0rd@foobar.baz.com/Apache_log
Context: main server config
Defines the basic connection URI to connect to the database with. The format of the connection URI is
driver://username[:password]@hostname[:port]/database
This is defined only once in the httpd.conf file.
This directive Must be defined for logging to be enabled.
LogSQLDBParam {parameter-name} {value}
Example: LogSQLDBParam socketfile /var/lib/mysql/mysql.socket
Context: main server config
This is the new method of specifying Database connection credentials and settings. This is used to define database driver specific options. For a list of options read the documentation for each specific database driver.
Each parameter-name may only be defined once.
LogSQLCreateTables {flag}
Example: LogSQLCreateTables On
Default: Off
Context: main server config
mod_log_sql has the ability to create its tables on-the-fly. The advantage to this is convenience: you don't have to execute any SQL by hand to prepare the table. This is especially helpful for people with lots of virtual hosts (who should also see the LogSQLMassVirtualHosting directive).
There is a slight disadvantage: if you wish to activate this feature, then the userid specified in LogSQLLoginInfo must have CREATE privileges on the database. In an absolutely paranoid, locked-down situation you may only want to grant your mod_log_sql user INSERT privileges on the database; in that situation you are unable to take advantage of LogSQLCreateTables. But most people -- even the very security-conscious -- will find that granting CREATE on the logging database is reasonable.
This is defined only once in the httpd.conf file.
LogSQLForcePreserve {flag}
Example: LogForcePreserve On
Default: Off
Context: main server config
You may need to perform debugging on your database and specifically want mod_log_sql to make no attempts to log to it. This directive instructs the module to send all its log entries directly to the preserve file and to make no database INSERT attempts.
This is presumably a directive for temporary use only; it could be dangerous if you set it and forget it, as all your entries will simply pile up in the preserve file.
This is defined only once in the httpd.conf file.
LogSQLDisablePreserve {flag}
Example: LogDisablePreserve On
Default: Off
Context; main server config
This option can be enabled to completely disable the preserve file fail back. This may be useful for servers where the file-system is read-only.
If the database is not available those log entries will be lost.
This is defined only once in the httpd.conf file.
LogSQLMachineID {machineID}
Example: LogSQLMachineID web01
Context: main server config
If you have a farm of webservers then you may wish to know which particular machine made each entry; this is useful for analyzing your load-balancing methodology. LogSQLMachineID permits you to distinguish each machine's entries if you assign each machine its own LogSQLMachineID: for example, the first webserver gets ``LogSQLMachineID web01,'' the second gets ``LogSQLMachineID web02,'' etc.
This is defined only once in the httpd.conf file.
LogSQLPreserveFile {filename}
Example: LogSQLPreserveFile offline-preserve
Default: /tmp/sql-preserve
Context: virtual host
mod_log_sql writes queries to this local preserve file in the event that it cannot reach the database, and thus ensures that your high-availability web frontend does not lose logs during a temporary database outage. This could happen for a number of reasons: the database goes offline, the network breaks, etc. You will not lose entries since the module has this backup. The file consists of a series of SQL statements that can be imported into your database at your convenience; furthermore, because the SQL queries contain the access timestamps you do not need to worry about out-of-order data after the import, which is done in a simple manner:
# mysql -uadminuser -p mydbname < /tmp/sql-preserve
If you do not define LogSQLPreserveFile then all virtual servers will log to the same default preserve file (/tmp/sql-preserve). You can redefine this on a virtual-host basis in order to segregate your preserve files if you desire. Note that segregation is not usually necessary, as the SQL statements that are written to the preserve file already distinguish between different virtual hosts if you include the 'v' character in your LogSQLTransferLogFormat directive. It is only necessary to segregate preserve-files by virualhost if you also segregate access logs by virtualhost.
The module will log to Apache's ErrorLog when it notices a database outage, and upon database return. You will therefore know when the preserve file is being used, although it is your responsibility to import the file.
The file does not need to be created in advance. It is safe to remove or rename the file without interrupting Apache, as the module closes the filehandle immediately after completing the write. The file is created with the user & group ID of the running Apache process (e.g. 'nobody' on many Linux distributions).
LogSQLTransferLogTable {table-name}
Example: LogSQLTransferLogTable access_log_table
Context: virtual host
Defines which table is used for logging of Apache's transfers; this is analogous to Apache's TransferLog directive. table-name must be a valid table within the database defined in the LogSQLLoginInfo connection URI.
This directive is not necessary if you declare LogSQLMassVirtualHosting On, since that directive activates dynamically-named tables. If you attempt to use LogSqlTransferlogTable at the same time a warning will be logged and it will be ignored, since LogSQLMassVirtualHosting takes priority.
Requires unless LogSQLMassVirtualHosting is set to On
LogSQLCookieLogTable {table-name}
Example: LogSQLCookieLogTable cookie_log
Default: cookies
Context: virtual host
Defines which table is used for logging of cookies. Working in conjunction with LogSQLWhichCookies, you can log many of each request's associated cookies to a separate table. For meaningful data retrieval the cookie table is keyed to the access table by the unique request ID supplied by the standard Apache module mod_unique_id.
You must create the table (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to "on".
LogSQLHeadersInLogTable {table-name}
Example: LogSQLHeadersInLogTable headers
Default: headers_in
Context: virtual host
Defines which table is used for logging of inbound headers. Working in conjunction with LogSQLWhichHeadersIn, you can log many of each request's associated headers to a separate table. For meaningful data retrieval the headers table is keyed to the access table by the unique request ID supplied by the standard Apache module mod_unique_id.
Note that you must create the table (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to "on".
LogSQLHeadersOutLogTable {table-name}
Example: LogSQLHeadersOutLogTable headers
Default: headers_out
Context: virtual host
Defines which table is used for logging of outbound headers. Working in conjunction with LogSQLWhichHeadersOut, you can log many of each request's associated headers to a separate table. For meaningful data retrieval the headers table is keyed to the access table by the unique request ID supplied by the standard Apache module mod_unique_id.
Note that you must create the table (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to "on".
LogSQLNotesLogTable {table-name}
Example: LogSQLNotesLogTable notes-log
Default: notes
Context: virtual_host
Defines which table is used for logging of notes. Working in conjunction with LogSQLWhichNotes, you can log many of each request's associated notes to a separate table. For meaningful data retrieval the notes table is keyed to the access table by the unique request ID supplied by the standard Apache module mod_unique_id.
This table must be created (see create-tables.sql included in the package), or LogSQLCreateTables must be set to 'On'.
LogSQLMassVirtualHosting {flag}
Example: LogSQLMassVirtualHosting On
Default: Off
Context: main server config
If you administer a site hosting many, many virtual hosts then this option will appeal to you. If you turn on LogSQLMassVirtualHosting then several things happen:
the on-the-fly table creation feature is activated automatically
the transfer log table name is dynamically set from the virtual host's name after stripping out SQL-unfriendly characters (example: a virtual host www.grubbybaby.com gets logged to table access_www_grubbybaby_com)
which, in turn, means that each virtual host logs to its own segregated table. Because there is no data shared between virtual servers you can grant your users access to the tables they need; they will be unable to view others' data.
This is a huge boost in convenience for sites with many virtual servers. Activating LogSQLMassVirtualHosting obviates the need to create every virtual server's table and provides more granular security possibilities.
This is defined only once in the httpd.conf file.
LogSQLTransferLogFormat {format-string}
Example: LogSQLTransferLogFormat huSUTv
Default: AbHhmRSsTUuv
Context: virtual host
Each character in the format-string defines an attribute of the request that you wish to log. The default logs the information required to create Combined Log Format logs, plus several extras. Here is the full list of allowable keys, which sometimes resemble their Apache counterparts, but do not always:
Table 5. Core LogFormat parameters
| Symbol | Meaning | DB Field | Data Type | Example |
|---|---|---|---|---|
| A | User Agent | agent | varchar(255) | Mozilla/4.0 (compat; MSIE 6.0; Windows) |
| a | CGi request arguments | request_args | varchar(255) | user=Smith&cart=1231&item=532 |
| b | Bytes transfered | bytes_sent | int unsigned | 32561 |
| c??? | Text of cookie | cookie | varchar(255) | Apache=sdyn.fooonline.net 1300102700823 |
| f | Local filename requested | request_file | varchar(255) | /var/www/html/books-cycroad.html |
| H | HTTP request_protocol | request_protocol | varchar(10) | HTTP/1.1 |
| h | Name of remote host | remote_host | varchar(50) | blah.foobar.com |
| I | Request ID (from modd_unique_id) | id | char(19) | POlFcUBRH30AAALdBG8 |
| l | Ident user info | remote_logname | varcgar(50) | bobby |
| M | Machine ID??? | machine_id | varchar(25) | web01 |
| m | HTTP request method | request_method | varchar(10) | GET |
| P | httpd cchild PID | child_pid | smallint unsigned | 3215 |
| p | http port | server_port | smallint unsigned | 80 |
| R | Referer | referer | varchar(255) | http://www.biglinks4u.com/linkpage.html |
| r | Request in full form | request_line | varchar(255) | GET /books-cycroad.html HTTP/1.1 |
| S | Time of request in UNIX time_t format | time_stamp | int unsigned | 1005598029 |
| T | Seconds to service request | request_duration | smallint unsigned | 2 |
| t | Time of request in human format | request_time | char(28) | [02/Dec/2001:15:01:26 -0800] |
| U | Request in simple form | request_uri | varchar(255) | /books-cycroad.html |
| u | User info from HTTP auth | remote_user | varchar(50) | bobby |
| v | Virtual host servicing the request | virtual_host | varchar(255) | www.foobar.com |
| V | requested Virtual host name (mass virtualhosting) | virtual_host | varchar(255) | www.foobar.org |
[1] You must also specify LogSQLWhichCookie for this to take effect.
[2] You must also specify LogSQLmachineID for this to take effect.
Table 6. SSL LogFormat Parameters
| Symbol | Meaning | DB Field | Data Type | Example |
|---|---|---|---|---|
| z | SSL cipher used | ssl_cipher | varchar(25) | RC4-MD5 |
| q | Keysize of the SSL connection | ssl_keysize | smallint unsigned | 56 |
| Q | maximum keysize supported | ssl_maxkeysize | smallint unsigned | 128 |
LogSQLRemhostIgnore {hostname...}
Example: LogSQLRemhostIgnore localnet.com
Context: virtual host
Lists a series of smortrings that, if present in the REMOTE_HOST, will cause that request to not be logged. This directive is useful for cutting down on log clutter when you are certain that you want to ignore requests from certain hosts, such as your own internal network machines. See section Instructing the module what NOT to log using filtering directives for some tips for using this directive.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
Each string is separated by a space, and no regular expressions or globbing are allowed. Each string is evaluated as a substring of the REMOTE_HOST using strstr(). The comparison is case sensitive.
LogSQLRequestAccept {substring...}
Example: LogSQLRequestAccept .html .php .jpg
Default: if not specified, all requests are 'accepted'
Context: virtual host
Lists a series of strings that, if present in the URI, will permit that request to be considered for logging (depending on additional filtering by the "ignore" directives). Any request that fails to match one of the LogSQLRequestAccept entries will be discarded.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
This directive is useful for cutting down on log clutter when you are certain that you only want to log certain kinds of requests, and just blanket-ignore everything else. See section Instructing the module what NOT to log using filtering directives for some tips for using this directive.
Each string is separated by a space, and no regular expressions or globbing are allowed. Each string is evaluated as a substring of the URI using strstr(). The comparison is case sensitive.
This directive is completely optional. It is more general than LogSQLRequestIgnore and is evaluated before LogSQLRequestIgnore . If this directive is not used, all requests are accepted and passed on to the other filtering directives. Therefore, only use this directive if you have a specific reason to do so.
LogSQLRequestIgnore {substring...}
Example: LogSQLRequestIgnore root.exe cmd.exe default.ida favicon.ico
Context: virtual host
Lists a series of strings that, if present in the URI, will cause that request to NOT be logged. This directive is useful for cutting down on log clutter when you are certain that you want to ignore requests for certain objects. See section Instructing the module what NOT to log using filtering directives for some tips for using this directive.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
Each string is separated by a space, and no regular expressions or globbing are allowed. Each string is evaluated as a substring of the URI using strstr(). The comparison is case sensitive.
LogSQLWhichCookie {cookiename}
Example; LogSQLWhichCookie Clicks
Context: virtual host
In HTTP, cookies have names to distinguish them from each other. Using mod_usertrack, for example, you can give your user-tracking cookies a name with the CookieName directive.
mod_log_sql allows you to log cookie information. LogSQL_WhichCookie tells mod_log_sql which cookie to log. This is necessary because you will usually be setting and receiving more than one cookie from a client.
You must include a 'c' character in LogSQLTransferLogFormat for this directive to take effect.
although this was origintally intended for people using mod_usertrack to create user-tracking cookies, you are not restricted in any way. You can choose which cookie you wish to log to the database - any cookie at all - and it does not necessarily have to have anything to do with mod_usertrack.
LogSQLWhichCookies {cookie-name...}
Example: logSQLWhichCookies userlogin cookie1 cookie2
Context: virtual host
Defines the list of cookies you would like logged. This works in conjunction with LogSQLCookieLogTable. This directive does not require any additional characters to be added to the LogSQLTransferLogFormat string. The feature is activated simply by including this directive, upon which you will begin populating the separate cookie table with data.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
The table must be created (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to 'On'.
LogSQLWhichHeadersIn {header-name...}
Example: LogSQLWhichHeadersIn UserAgent Accept-Encodeing Host
Context: virtual host
Defines the list of inbound headers you would like logged. This works in conjunction with LogSQLHeadersInLogTable. This directive does not require any additional characters to be added to the LogSQLTransferLogFormat string. The feature is activated simply by including this directive, upon which you will begin populating the separate inbound-headers table with data.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
The table must be created (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to 'On'.
LogSQLWhichHeadersOut {header-name...}
Example: LogSQLWhichHeadersOut Expires Content-Type Cache-Control
Context: virtual host
Defines the list of outbound headers you would like logged. This works in conjunction with LogSQLHeadersOutLogTable. This directive does not require any additional characters to be added to the LogSQLTransferLogFormat string. The feature is activated simply by including this directive, upon which you will begin populating the separate outbound-headers table with data.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
The table must be created (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to 'On'.
LogSQLWhichNotes {note-name...}
Example: LogSQLWhichNotes mod_gzip_result mod_gzip_ompression_ratio
Context: virtual host
Defines the list of notes you would like logged. This works in conjunction with LogSQLNotesLogTable. This directive does not require any additional characters to be added to the LogSQLTransferLogFormat string. The feature is activated simply by including this directive, upon which you will begin populating the separate notes table with data.
Each string may contain a + or - prefix in a <VirtualHost> context and will cause those strings to be added (+) or removed (-) from the global configuration. Otherwise the global is completely ignored and overridden if defined in a <VirtualHost>
The table must be created (see create-tables.sql, included in the package), or LogSQLCreateTables must be set to 'On'.
LogSQLSocketFile {filename}
Example: LogSQLSocketFile /tmp/mysql.sock
Default: (database specific)
Default (MySQL): /var/lib/mysql/mysql.sock
Context: main server config
At Apache runtime you can specify the MySQL socket file to use. Set this once in your main server config to override the default value. This value is irrelevant if your database resides on a separate machine.
mod_log_sql will automatically employ the socket for db communications if the database resides on the local host. If the db resides on a separate host the module will automatically use TCP/IP. This is a function of the MySQL API and is not user-configurable.
This directive is deprecated in favor of LogSQLDBParam socketfile [socketfilename]
This is defined only once in the httpd.conf file.
LogSQLTCPPort {port-number}
Example: LogSQLTCPPort 3309
Default: (database specific)
Default (MySQL): 3306
Context: main server config
Your database may listen on a different port than the default. If so, use this directive to instruct the module which port to use. This directive only applies if the database is on a different machine connected via TCP/IP.
This directive is deprecated in favor of LogSQLDBParam tcpport [port-number]
This is defined only once in the httpd.conf file.
LogSQLDatabase {database}
Example: LogSQLDatabase loggingdb
Context: main server config
Defines the database that is used for logging. "database" must be a valid db on the MySQL host defined in LogSQLLoginInfo
This directive is deprecated in favor of the URI form of LogSQLLoginInfo.
This is defined only once in the httpd.conf file.
1. General module questions | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.1. | Why log to an SQL database? | ||||||||||||||||||||||||||||||||||||||||||||||||||
To begin with, let's get it out of the way: logging to a database is not a panacea. But while there are complexities with this solution, the benefit can be substantial for certain classes of administrator or people with advanced requirements:
For example, do you want to see all your 404's? Do this: select remote_host,status,request_uri,bytes_sent,from_unixtime(time_stamp) from acc_log_tbl where status=404 order by time_stamp; Table 7.
Or do you want to see how many bytes you've sent within a certain directory or site? Do this: select request_uri,sum(bytes_sent) as bytes,count(request_uri) as howmany from acc_log_tbl where request_uri like '%mod_log_sql%' group by request_uri order by howmany desc; Table 8.
Or maybe you want to see who's linking to you? Do this: select count(referer) as num,referer from acc_log_tbl where request_uri='/mod_log_sql/' group by referer order by num desc; Table 9.
As you can see, there are myriad possibilities that can be constructed with the wonderful SQL SELECT statement. Logging to an SQL database can be really quite useful! | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.2. | Why use MySQL? Are there alternatives? | ||||||||||||||||||||||||||||||||||||||||||||||||||
MySQL is a robust, free, and very powerful production-quality database engine. It is well supported and comes with detailed documentation. Many 3rd-party software pacakges (e.g. Slashcode, the engine that powers Slashdot) run exclusively with MySQL. In other words, you will belong to a very robust and well-supported community by choosing MySQL. That being said, there are alternatives. PostgreSQL is probably MySQL's leading "competitor" in the free database world. There is also an excellent module available for Apache to permit logging to a PostgreSQL database, called pgLOGd | |||||||||||||||||||||||||||||||||||||||||||||||||||
NoteCurrently a database abstraction system is in the works to allow any database to be used with mod_log_sql. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.3. | Is this code production-ready? | ||||||||||||||||||||||||||||||||||||||||||||||||||
By all accounts it is. It is known to work without a problem on many-thousands-of-hits-per-day webservers. Does that mean it is 100% bug free? Well, no software is, but it is well-tested and believed to be fully compatible with production environments. (The usual disclaimers apply. This software is provided without warranty of any kind.) | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.4. | Who's using mod_log_sql? | ||||||||||||||||||||||||||||||||||||||||||||||||||
Good question! It would be great to find out! If you are a production-level mod_log_sql user, please contact eddie at <urkle <at> outoforder <dot> cc> so that you can be mentioned here. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.5. | Why doesn't the module also replace the Apache ErrorLog? | ||||||||||||||||||||||||||||||||||||||||||||||||||
There are circumstances when that would be quite unwise -- for example, if Apache could not reach the MySQL server for some reason and needed to log that fact. Without a text-based error log you'd never know anything was wrong, because Apache would be trying to log a database connection error to the database... you get the point. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Error logs are usually not very high-traffic and are really best left as text files on a web server machine. | |||||||||||||||||||||||||||||||||||||||||||||||||||
The Error log is free format text.. (no specified formatting what, so ever) which is rather difficult to nicely format for storing in a database. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.6. | Does mod_log_sql work with Apache 2.x? | ||||||||||||||||||||||||||||||||||||||||||||||||||
Yes. A port of mod_log_sql is available for Apache 2.x as of mod_log_sql 1.90 | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.7. | Does mod_log_sql connect to MySQL via TCP/IP or a socket? | ||||||||||||||||||||||||||||||||||||||||||||||||||
Quick answer, Yes. | |||||||||||||||||||||||||||||||||||||||||||||||||||
It depends! This is not determined by mod_log_sql. mod_log_sql relies on a connection command that is supplied in the MySQL API, and that command is somewhat intelligent. How it works:
You don't have any control of which methodology is used. You can fine-tune some of the configuration, however. The LogSQLSocketFile runtime configuration directive overrides the default of "/var/lib/mysql/mysql.sock" for socket-based connections, whereas the LogSQLTCPPort command allows to you override the default TCP port of 3306 for TCP/IP connections. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 1.8. | I have discovered a bug. Who can I contact? | ||||||||||||||||||||||||||||||||||||||||||||||||||
Please contact Edward Rudd at <urkle <at> outoforder <dot> cc>, or post a message to the mod_log_sql Mailing Lists. Your comments, suggestions, bugfixes, bug catches, and usage testimonials are always welcome. As free software, mod_log_sql is intended to be a community effort -- any code contributions or other ideas will be fully and openly credited, of course. | |||||||||||||||||||||||||||||||||||||||||||||||||||
2. Problems | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.1. | Apache segfaults or has other problems when using PHP and mod_log_sql | ||||||||||||||||||||||||||||||||||||||||||||||||||
This occurs if you compiled PHP with MySQL database support. PHP utilizes its internal, bundled MySQL libraries by default. These conflict with the "real" MySQL libraries linked by mod_log_sql, causing the segmentation fault. PHP and mod_log_sql can be configured to happily coexist. The solution is to configure PHP to link against the real MySQL libraries: recompile PHP using --with-mysql=/your/path. Apache will run properly once the modules are all using the same version of the MySQL libraries. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.2. | Apache appears to start up fine, but nothing is getting logged in the database | ||||||||||||||||||||||||||||||||||||||||||||||||||
If you do not see any entries in the access_log, then something is preventing the inserts from happening. This could be caused by several things:
NoteIt is improper to ask for help before you have followed these steps. First examine the MySQL log that you established in step 6 of section Preparing MySQL for logging. Ensure that the INSERT statements are not being rejected because of a malformed table name or other typographical error. By enabling that log, you instructed MySQL to log every connection and command it receives -- if you see no INSERT attempts in the log, the module isn't successfully connecting to the database. If you see nothing at all in the log -- not even a record of your administrative connection attempts, then you did not enable the log correctly. If you do see INSERT attempts but they are failing, the log should tell you why. Second, confirm that your LogSQL* directives are all correct. Third, examine the Apache error logs for messages from mod_log_sql; the module will offer hints as to why it cannot connect, etc. The next thing to do is to change the LogLevel directive in the main server config as well as in each VirtualHost config: LogLevel debug ErrorLog /var/log/httpd/server-messages | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.3. | Why do I get the message "insufficient configuration info to establish database link" in my Apache error log? | ||||||||||||||||||||||||||||||||||||||||||||||||||
At a minimum, LogSQLLoginInfo in the URl form and either LogSQLTableName or LogSQLMassVirtualHosting must be defined in order for the module to be able to establish a database link. If these are not defined or are incomplete you will receive this error message. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.4. | My database cannot handle all the open connections from mod_log_sql, is there anything I can do? | ||||||||||||||||||||||||||||||||||||||||||||||||||
The rule of thumb: if you have n webservers each configured to support y MaxClients, then your database must be able to handle n times y simultaneous connections in the worst case. Certainly you must use common sense, consider reasonable traffic expectations and structure things accordingly. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Tweaking my.cnf to scale to high connection loads is imperative. But if hardware limitations prevent your MySQL server from gracefully handling the number of incoming connections, it would be beneficial to upgrade the memory or CPU on that server in order to handle the load. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Jeremy Zawodny, a highly respected MySQL user and contributor to Linux Magazine, has this very helpful and highly appropriate article on tuning MySQL: MySQL, Linux, and Thread Caching | |||||||||||||||||||||||||||||||||||||||||||||||||||
Please remember that mod_log_sql's overriding principle is performance -- that is what the target audience demands and expects. Other database logging solutions do not open and maintain many database connections, but their performance suffers drastically. For example, pgLOGd funnels all log connections through a separate daemon that connects to the database, but that bottlenecks the entire process. mod_log_sql achieves performance numbers an order of magnitude greater than the alternatives because it dispenses with the overhead associated with rapid connection cycling, and it does not attempt to shoehorn all the database traffic through a single extra daemon or proxy process. | |||||||||||||||||||||||||||||||||||||||||||||||||||
NoteCurrently connection pooling is being implemented as part of the Database Abstraction layer to allow multiple httpd processes to share connections. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.5. | Why do I occasionally see a "lost connection to MySQL server" message in my Apache error log? | ||||||||||||||||||||||||||||||||||||||||||||||||||
This message may appear every now and then in your Apache error log, especially on very lightly loaded servers. This does not mean that anything is necessarily wrong. Within each httpd child process, mod_log_sql will open (and keep open) a connection to the MySQL server. MySQL, however, will close connections that have not been used in a while; the default timeout is 8 hours. When this occurs, mod_log_sql will notice and re-open the connection. That event is what is being logged, and looks like this: [Tue Nov 12 19:04:10 2002] [error] mod_log_sql: first attempt failed, API said: error 2013, Lost connection to MySQL server during query [Tue Nov 12 19:04:10 2002] [error] mod_log_sql: reconnect successful [Tue Nov 12 19:04:10 2002] [error] mod_log_sql: second attempt successful Reference: MySQL documentation | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 2.6. | Sometimes a single VirtualHost gets logged to two different tables (e.g. access_foo_com, access_www_foo_com). Or, accesses to an unqualified hostname (e.g. "http://intranet/index.html") get logged in separate tables. | ||||||||||||||||||||||||||||||||||||||||||||||||||
Proper usage of the Apache runtime ServerName directive and the directive UseCanonicalName On (or DNS) are necessary to prevent this problem. "On" is the default for UseCanonicalName, and specifies that self-referential URLs are generated from the ServerName part of your VirtualHost: With UseCanonicalName on (and in all versions prior to 1.3) Apache will use the ServerName and Port directives to construct the canonical name for the server. With UseCanonicalName off Apache will form self-referential URLs using the hostname and port supplied by the client if any are supplied (otherwise it will use the canonical name, as defined above). [From the Apache documentation] The module inherits Apache's "knowledge" about the server name being accessed. As long as those two directives are properly configured, mod_log_sql will log to only one table per virtual host while using LogSQLMassVirtualHosting. | |||||||||||||||||||||||||||||||||||||||||||||||||||
3. Performance and Tuning | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 3.1. | How well does it perform? | ||||||||||||||||||||||||||||||||||||||||||||||||||
mod_log_sql scales to very high loads. Apache 1.3.22 + mod_log_sql was benchmarked using the "ab" (Apache Bench) program that comes with the Apache distribution; here are the results. Overall configuration
Example 2. Apache configuration Timeout 300 KeepAlive On MaxKeepAliveRequests 100 KeepAliveTimeout 15 MinSpareServers 5 StartServers 10 MaxSpareServers 15 MaxClients 256 MaxRequestsPerChild 5000 LogSQLTransferLogFormat AbHhmRSsTUuvc LogSQLWhichCookie Clicks CookieTracking on CookieName Clicks Example 3. "ab" commandline ./ab -c 10 -t 20 -v 2 -C Clicks=ab_run http://www.hostname.com/target ( 10 concurrent requests; 20 second test; setting a cookie "Clicks=ab_run"; target = the mod_log_sql homepage. ) Ten total ab runs were conducted: five with MySQL logging enabled, and five with all MySQL directives commented out of httpd.conf. Then each five were averaged. The results:
In other words, any rate-limiting effects on this particular hardware setup are not caused by MySQL. Note that although this very simple webserver setup is hardly cutting-edge -- it is, after all, a fairly small machine -- 139 requests per second equal over twelve million hits per day. If you run this benchmark yourself, take note of three things:
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| 3.2. | Do I need to be worried about all the running MySQL children? Will holding open n Apache-to-MySQL connections consume a lot of memory? | ||||||||||||||||||||||||||||||||||||||||||||||||||
Short answer: you shouldn't be worried. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Long answer: you might be evaluating at the output of "ps -aufxw" and becoming alarmed at all the 7MB httpd processes or 22MB mysqld children that you see. Don't be alarmed. It's true that mod_log_sql opens and holds open many MySQL connections: each httpd child maintains one open database connection (and holds it open for performance reasons). Four webservers, each running 20 Apache children, will hold open 80 MySQL connections, which means that your MySQL server needs to handle 80 simultaneous connections. In truth, your MySQL server needs to handle far more than that if traffic to your website spikes and the Apache webservers spawn off an additional 30 children each... Fortunately the cost reported by 'ps -aufxw' is deceptive. This is due to an OS memory-management feature called "copy-on-write." When you have a number of identical child processes (e.g. Apache, MySQL), it would appear in "ps" as though each one occupies a great deal of RAM -- as much as 7MB per httpd child! In actuality each additional child only occupies a small bit of extra memory -- most of the memory pages are common to each child and therefore shared in a "read-only" fashion. The OS can get away with this because the majority of memory pages for one child are identical across all children. Instead of thinking of each child as a rubber stamp of the others, think of each child as a basket of links to a common memory area. A memory page is only duplicated when it needs to be written to, hence "copy-on-write." The result is efficiency and decreased memory consumption. "ps" may report 7MB per child, but it might really only "cost" 900K of extra memory to add one more child. It is not correct to assume that 20 Apache children with a VSZ of 7MB each equals (2 x 7MB) of memory consumption -- the real answer is much, much lower. The same "copy-on-write" rules apply to all your MySQL children: 40 mysqld children @ 22MB each do not occupy 880MB of RAM. The bottom line: although there is a cost to spawn extra httpd or mysqld children, that cost is not as great as "ps" would lead you to believe. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 3.3. | My webserver cannot handle all the traffic that my site receives, is there anything I can do? | ||||||||||||||||||||||||||||||||||||||||||||||||||
If you have exhausted all the tuning possibilities on your existing server, it is probably time you evaluated the benefits of clustering two or more webservers together in a load-balanced fashion. In fact, users of such a setup are mod_log_sql's target audience! | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 3.4. | What is the issue with activating delayed inserts? | ||||||||||||||||||||||||||||||||||||||||||||||||||
INSERT DELAYED is a specific syntax to MySQL and is not supported by any other database. Ergo, why is it needed, and what MySQL deficiency is it working around? INSERT DELAYED is a kluge. | |||||||||||||||||||||||||||||||||||||||||||||||||||
The MySQL documentation is unclear whether INSERT DELAYED is even necessary for an optimized database. It says, "The DELAYED option for the INSERT statement is a MySQL-specific option that is very useful if you have clients that can't wait for the INSERT to complete." But then it goes on to say, "Note that as MyISAM tables supports concurrent SELECT and INSERT, if there is no free blocks in the middle of the data file, you very seldom need to use INSERT DELAYED with MyISAM." | |||||||||||||||||||||||||||||||||||||||||||||||||||
Because INSERT DELAYED returns without waiting for the data to be written, a hard kill of your MySQL database at the right (wrong?) moment could lose those logfile entries. | |||||||||||||||||||||||||||||||||||||||||||||||||||
As of MySQL version 3.23.52, the error return functions disagree after a failed INSERT DELAYED: mysql_errno() always returns 0, even if mysql_error() returns a textual error. I have reported this bug to the MySQL folks. However, we have no way of knowing what solution they will adopt to fix this, and with the worst case solution mod_log_sql would not be able to tell if anything went wrong with a delayed insert. | |||||||||||||||||||||||||||||||||||||||||||||||||||
Instead of delayed inserts, you may wish to utilize InnoDB tables (instead of the standard MyISAM tables). InnoDB tables suppot row-level locking and are recommended for high-volume databases. | |||||||||||||||||||||||||||||||||||||||||||||||||||
If after understanding these problems you still wish to enable delayed inserts, section Optimizing for a busy database discusses how. | |||||||||||||||||||||||||||||||||||||||||||||||||||
4. "How do I...?" -- accomplishing certain tasks | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 4.1. | How do I extract the data in a format that my analysis tool can understand? | ||||||||||||||||||||||||||||||||||||||||||||||||||
mod_log_sql would be virtually useless if there weren't a way for you to extract the data from your database in a somewhat meaningful fashion. To that end there's a Perl script enclosed with the distribution. That script (make_combined_log.pl) is designed to extract N-many days worth of access logs and provide them in a Combined Log Format output. You can use this very tool right in /etc/crontab to extract logs on a regular basis so that your favorite web analysis tool can read them. Or you can examine the Perl code to construct your own custom tool. For example, let's say that you want your web statistics updated once per day in the wee hours of the morning. A good way to accomplish that could be the following entries in /etc/crontab: # Generate the temporary apache logs from the MySQL database (for webalizer) 05 04 * * * root make_combined_log.pl 1 www.grubbybaby.com > /var/log/temp01 # Run webalizer on httpd log 30 04 * * * root webalizer -c /etc/webalizer.conf; rm -f /var/log/temp01 Or if you have a newer system that puts files in /etc/cron.daily etc., create a file called "webalizer" in the cron.daily subdirectory. Use the following as the contents of your file, and make sure to chmod 755 it when done. #!/bin/sh /usr/local/sbin/make_combined_log.pl 1 www.yourdomain.com > /var/log/httpd/templog /usr/local/bin/webalizer -q -c /etc/webalizer.conf rm -f /var/log/httpd/templog See? Easy. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 4.2. | How can I log mod_usertrack cookies? | ||||||||||||||||||||||||||||||||||||||||||||||||||
A number of people like to log mod_usertrack cookies in their Apache TransferLog to aid in understanding their visitors' clickstreams. This is accomplished, for example, with a statement as follows: LogFormat "%h %l %u %t \"%r\" %s %b \"%{Referer}i\" \"%{User-Agent}i\"" \"%{cookie}n\""Naturally it would be nice for mod_log_sql to permit the admin to log the cookie data as well, so as of version 1.10 you can do this. You need to have already compiled mod_usertrack into httpd -- it's one of the standard Apache modules. First make sure you have a column called "cookie" in the MySQL database to hold the cookies, which can be done as follows if you already have a working database: mysql> alter table acc_log_tbl add column cookie varchar(255); Next configure your server to set usertracking cookies as follows, and make sure you include the new 'c' directive in your LogSQLTransferLogFormat, which activates cookie logging. Here's an example: <VirtualHost 1.2.3.4> CookieTracking on CookieStyle Cookie CookieName Foobar LogSQLTransferLogFormat huSUsbTvRAc LogSQLWhichCookie Foobar </VirtualHost> The first three lines configure mod_usertrack to create a COOKIE (RFC 2109) format cookie called Foobar. The last two lines tell mod_log_sql to log cookies named Foobar. You have to choose which cookie to log because more than one cookie can/will be sent to the server by the client. Recap: the 'c' character activates cookie logging, and the LogSQLWhichCookie directive chooses which cookie to log. FYI, you are advised NOT to use CookieStyle Cookie2 -- it seems that even newer browsers (IE 5.5, etc.) have trouble with the new COOKIE2 (RFC 2965) format. Just stick with the standard COOKIE format and you'll be fine. Perform some hits on your server and run a select mysql> select request_uri,cookie from access_log where cookie is not null; Table 10.
| |||||||||||||||||||||||||||||||||||||||||||||||||||
| 4.3. | What if I want to log more than one cookie? What is the difference between LogSQLWhichCookie and LogSQLWhichCookies? | ||||||||||||||||||||||||||||||||||||||||||||||||||
As of version 1.17, you have a choice in how you want cookie logging handled. If you are interested in logging only one cookie per request, follow the instructions in FAQ entry Q: 4.2. above. That cookie will be logged to a column in the regular access_log table, and the actual cookie you want to log is specified with LogSQLWhichCookie. Don't forget to specify the 'c' character in LogSQLTransferLogFormat. If, however, you need to log multiple cookies per request, you must employ the LogSQLWhichCookies (note the plural) directive. The cookies you specify will be logged to a separate table (as discussed in section Logging many-to-one data in separate tables), and entries in that table will be linked to the regular access_log entries via the unique ID that is supplied by mod_unique_id. Without mod_unique_id the information will still be logged but you will be unable to correlate which cookies go with which access-requests. Furthermore, with LogSQLWhichCookies, you do not need to include the 'c' character in LogSQLTransferLogFormat. LogSQLWhichCookie and LogSQLWhichCookies can coexist without conflict because they operate on entireley different tables, but you're better off choosing the one you need. | |||||||||||||||||||||||||||||||||||||||||||||||||||
| 4.4. | What are the SSL logging features, and how do I activate them? | ||||||||||||||||||||||||||||||||||||||||||||||||||
NoteYou do not need to compile SSL support into mod_log_sql in order to simply use it with a secure site. You only need to compile SSL support into mod_log_sql if you want to log SSL-specific data such as the cipher type used, or the keysize that was negotiated. If that information is unimportant to you, you can ignore this FAQ. By adding certain characters to your LogSQLTransferLogFormat string you can tell mod_log_sql to log the SSL cipher, the SSL keysize of the connection, and the maximum keysize that was available. This would let you tell, for example, which clients were using only export-grade security to access your secure software area. You can compile mod_log_sql with SSL logging support if you have the right packages installed. If you already have an SSL-enabled Apache then you by definition have the correct packages already installed: OpenSSL and mod_ssl. You need to ensure that your database is set up to log the SSL data. Issue the following commands to MySQL if your access table does not already have them: mysql> alter table access_log add column ssl_cipher varchar(25); mysql> alter table access_log add column ssl_keysize smallint unsigned; mysql> alter table access_log add column ssl_maxkeysize smallint unsigned; Finally configure httpd.conf to activate the SSL fields. Note that this is only meaningful in a VirtualHost that is set up for SSL. <VirtualHost 1.2.3.4:443> LogSQLTransferLogFormat AbHhmRSsTUuvcQqz </VirtualHost> You also need to make sure you have the mod_log_sql_ssl module loaded as well. The last three characters (Qqz) in the directive are the SSL ones; see section LogSQLTransferLogFormat in the directives documentation for details of the LogSQLTransferLogFormat directive. Restart Apache, then perform some hits on your server. Then run the following select statement: mysql> select remote_host,request_uri,ssl_cipher,ssl_keysize,ssl_maxkeysize from access_log where ssl_cipher is not null; Table 11.
| |||||||||||||||||||||||||||||||||||||||||||||||||||