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Server Log Maintenance

549

To include slow administrative statements in the statements written to the slow query log, use the

log-slow-admin-statements

[412]

server option. Administrative statements include

ALTER

TABLE

ANALYZE TABLE

CHECK TABLE

CREATE INDEX

DROP INDEX

OPTIMIZE TABLE

, and

REPAIR TABLE

To include queries that do not use indexes for row lookups in the statements written to the slow query
log, use the

--log-queries-not-using-indexes

[412]

server option. See

Section 5.1.3, “Server

Command Options”

. When such queries are logged, the slow query log may grow quickly.

The server uses the controlling parameters in the following order to determine whether to write a query
to the slow query log:

1. The query must either not be an administrative statement, or

--log-slow-admin-

statements

[412]

must have been specified.

2. The query must have taken at least

long_query_time

[465]

seconds, or

--log-queries-

not-using-indexes

[412]

must have been specified and the query used no indexes for row

lookups.

The server does not write queries handled by the query cache to the slow query log, nor queries that
would not benefit from the presence of an index because the table has zero rows or one row.

Replication slaves do not write replicated queries to the slow query log, even if the same queries were
written to the slow query log on the master. This is a known issue. (Bug #23300)

The slow query log should be protected because logged statements might contain passwords. See

Section 6.1.2.3, “Passwords and Logging”

The slow query log can be used to find queries that take a long time to execute and are therefore
candidates for optimization. However, examining a long slow query log can become a difficult task.
To make this easier, you can process a slow query log file using the

mysqldumpslow

command to

summarize the queries that appear in the log. See

Section 4.6.8, “

mysqldumpslow

— Summarize

Slow Query Log Files”

5.2.5. Server Log Maintenance

As described in

Section 5.2, “MySQL Server Logs”

, MySQL Server can create several different log files

to help you see what activity is taking place. However, you must clean up these files regularly to ensure
that the logs do not take up too much disk space.

When using MySQL with logging enabled, you may want to back up and remove old log files from time
to time and tell MySQL to start logging to new files. See

Section 7.2, “Database Backup Methods”

On a Linux (Red Hat) installation, you can use the

mysql-log-rotate

script for this. If you installed

MySQL from an RPM distribution, this script should have been installed automatically. Be careful with
this script if you are using the binary log for replication. You should not remove binary logs until you are
certain that their contents have been processed by all slaves.

On other systems, you must install a short script yourself that you start from

cron

(or its equivalent) for

handling log files.

For the binary log, you can set the

expire_logs_days

[450]

system variable to expire binary log

files automatically after a given number of days (see

Section 5.1.4, “Server System Variables”

). If you

are using replication, you should set the variable no lower than the maximum number of days your
slaves might lag behind the master. To remove binary logs on demand, use the

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