Slow Query Log Extended Statistics

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.

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:

• All (From MariaDB 10.6.16)
  • Enable all verbosity options.
• 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
  • EXPLAIN output is logged in the slow query log. See explain-in-the-slow-query-log for details.
• Innodb (From MariaDB 10.6.15. Before that this option did nothing)
  • Kept for compatibility. Same as engine.
• engine (From MariaDB 10.6.15)
  • Writes statistics from the storage engine. This includes:

• Warnings (From MariaDB 10.6.16)
  • Print all errors, warnings and notes related to statement, up to log_slow_max_warnings lines.
• full.
  • Old shortcut to enable all the verbosity options

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

The possible values for log_slow_verbosity are innodb,query_plan,explain,engine,warnings. Multiple options are separated by ','.

log_slow_verbosity is not supported when log_output='TABLE'.

In the future we will add more engine statistics and also support for other engines.

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:

• All (From MariaDB 10.6.16)
  • Enable all filter options. log_slow_filter will be shown as having all options set.
• admin
  • Log administrative statements (create, optimize, drop etc...)
  • log_slow_admin_statements maps to this option.
• filesort
  • Log statement if it uses filesort
• filesort_on_disk
  • Log statement if it uses filesort that needs temporary tables on disk
• filesort_priority_queue (from MariaDB 10.3.2)
  • Log statement if it uses filesort with priority_queue (filesort can either use disk or priority queue).
• full_join
  • Log statements that doesn't uses indexes to join tables
• full_scan
  • Log statements that uses full table scans
• not_using_index (From MariaDB 10.3.1)
  • Logs queries that don't use an index, or that perform a full index scan where the index doesn't limit the number of rows
  • Disregards long_query_time, unlike other options!
  • log_queries_not_using_indexes maps to this option
• 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 (same as setting the value to All

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).

log_slow_max_warnings

Credits

Part of this addition is based on the microslow patch from Percona.

See also

• Notes when an index cannot be used because of type conversions