The log_slow_rate_limit variable defines the fraction of queries captured by the slow query log. A good rule of thumb is to have approximately 100 queries logged per second. For example, if your Percona Server instance processes 10_000 queries per second, you should set log_slow_rate_limit to 100 and capture every 100th query for the slow query log.


When using query sampling, set log_slow_rate_type to query so that it applies to queries, rather than sessions.

It is also a good idea to set log_slow_verbosity to full so that maximum amount of information about each captured query is stored in the slow query log.

See also

MySQL Server 5.7 Documentation: Setting variables

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