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Displaying posts with tag: mysql error log (reset)
When is the error log filename not the right filename

When evaluating a MySQL system one of the first things to look at is the MySQL error log. This is defined by the log[_-]error variable in the MySQL Configuration file. Generally found like:

grep log.error /etc/my.cnf

It is possible to find multiple rows because this could be defined in the [mysqld] and [mysqld_safe] sections. It is also possible it is incorrectly defined twice in any given section.

Immediately I see a problem here, and the following describes why. If you look at this file name, in this case it’s actually found, but the file is empty.

$ ls -l /var/lib/mysql/logs/mysql_error_log
-rw-r----- 1 mysql mysql 0 Feb 19 20:35 /var/lib/mysql/logs/mysql_error_log

An error log should never exist and be empty, because starting the instance producing messages. An error log could be empty because the system does …

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Advanced InnoDB Deadlock Troubleshooting – What SHOW INNODB STATUS Doesn’t Tell You, and What Diagnostics You Should be Looking At

One common cause for deadlocks when using InnoDB tables is from the existence of foreign key constraints and the shared locks (S-lock) they acquire on referenced rows.

The reason I want to discuss them though is because they are often a bit tricky to diagnose, especially if you are only looking at the SHOW ENGINE INNODB STATUS output (which might be a bit counter-intuitive since one would expect it to contain this info).

Let me show a deadlock error to illustrate (below is from SHOW ENGINE INNODB STATUS\g):

111109 20:10:03
TRANSACTION 65839, ACTIVE 19 sec, OS thread id 4264 starting index read
mysql tables in use 1, locked 1
LOCK WAIT 6 lock struct(s), heap size 1024, 3 row lock(s), undo log entries 1
MySQL thread id 3, query id 74 localhost root Updating
UPDATE parent SET age=age+1 WHERE id=1
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The correct approach to rolling MySQL logs

I say correct because there are several incorrect approaches to managing MySQL logs. In MySQL you have two important log files, the MySQL error log (configured with –log-error) and the MySQL slow query log (configured with –log-slow-queries or –slow-query-log and –slow-query-log-file which is available …

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