MariaDB starting with 5.1

Extended statistics to the slow query log were introduced in MariaDB 5.1

This addition is based on the microslow patch from Percona.

Overview

  • Added extra logging to slow log of 'Thread_id, Schema, Query Cache hit, Rows sent and Rows examined'
  • Added optional logging to slow log, through log_slow_verbosity, of query plan statistics
  • Added new session variables log_slow_rate_limit, log_slow_verbosity, log_slow_filter
  • Added log-slow-file as synonym for 'slow-log-file', as most slow-log variables starts with 'log-slow'
  • Added log-slow-time as synonym for long-query-time.

New Session Variables

log_slow_verbosity

You can set the verbosity of what's logged to the slow query log by setting the the log_slow_verbosity variable to a combination of the following values:

  • Query_plan
    • For select queries, log information about the query plan. This includes "Full_scan", "Full_join", "Tmp_table", "Tmp_table_on_disk", "Filesort", "Filesort_on_disk" and number of "Merge_passes during sorting"
  • explain (Starting from 10.0.4)
  • Innodb
    • Reserved for future use.

The default value is ' ', to be compatible with MySQL 5.1.

Multiple options are separated by ','.

log_slow_filter

You can define which queries to log to the slow query log by setting the variable log_slow_filter to a combination of the following values:

  • admin
    • Log adminstrative statements (create, optimize, drop etc...)
  • filesort
    • Log statement if it uses filesort
  • filesort_on_disk
    • Log statement if it uses filesort that needs temporary tables on disk
  • full_join
    • Log statements that doesn't uses indexes to join tables
  • full_scan
    • Log statements that uses full table scans
  • query_cache
    • Log statements that are resolved by the query cache
  • query_cache_miss
    • Log statements that are not resolved by the query cache
  • tmp_table
    • Log statements that uses in memory temporary tables
  • tmp_table_on_disk
    • Log statements that uses temporary tables on disk

Multiple options are separated by ','. If you don't specify any options everything will be logged.

log_slow_rate_limit

The log_slow_rate_limit variable limits logging to the slow query log by not logging every query (only one query / log_slow_rate_limit is logged). This is mostly useful when debugging and you get too much information to the slow query log.

Note that in any case, only queries that takes longer than log_slow_time or long_query_time' are logged (as before).

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