Details
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Bug
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Status: Confirmed (View Workflow)
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Major
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Resolution: Unresolved
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10.5.6, 10.5.7
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None
Description
If we start MariaDB 10.5 with performance_schema enabled:
openxs@ao756:~/dbs/maria10.5$ bin/mysqld_safe --no-defaults --port=3311 --socket=/tmp/mariadb105.sock --performance_schema=1 &
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[1] 14213
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openxs@ao756:~/dbs/maria10.5$ 201011 13:34:47 mysqld_safe Logging to '/home/openxs/dbs/maria10.5/data/ao756.err'.
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201011 13:34:47 mysqld_safe Starting mariadbd daemon with databases from /home/openxs/dbs/maria10.5/data
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and check memory instrumentation summary tables immediately after start we can see negative values for memory/sql/global_system_variables and main thread:
openxs@ao756:~/dbs/maria10.5$ bin/mysql --socket=/tmp/mariadb105.sock performance_schema
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Reading table information for completion of table and column names
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You can turn off this feature to get a quicker startup with -A
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Welcome to the MariaDB monitor. Commands end with ; or \g.
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Your MariaDB connection id is 3
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Server version: 10.5.7-MariaDB Source distribution
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Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.
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Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
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MariaDB [performance_schema]> select * from memory_summary_by_host_by_event_name where current_number_of_bytes_used <0\G
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*************************** 1. row ***************************
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HOST: NULL
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EVENT_NAME: memory/sql/global_system_variables
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COUNT_ALLOC: 0
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COUNT_FREE: 2
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SUM_NUMBER_OF_BYTES_ALLOC: 0
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SUM_NUMBER_OF_BYTES_FREE: 128
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LOW_COUNT_USED: -2
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CURRENT_COUNT_USED: -2
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HIGH_COUNT_USED: 0
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LOW_NUMBER_OF_BYTES_USED: -128
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CURRENT_NUMBER_OF_BYTES_USED: -128
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HIGH_NUMBER_OF_BYTES_USED: 0
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1 row in set (0,002 sec)
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MariaDB [performance_schema]> select * from memory_summary_by_thread_by_event_name where current_number_of_bytes_used <0\G
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*************************** 1. row ***************************
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THREAD_ID: 1
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EVENT_NAME: memory/sql/global_system_variables
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COUNT_ALLOC: 0
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COUNT_FREE: 2
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SUM_NUMBER_OF_BYTES_ALLOC: 0
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SUM_NUMBER_OF_BYTES_FREE: 128
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LOW_COUNT_USED: -2
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CURRENT_COUNT_USED: -2
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HIGH_COUNT_USED: 0
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LOW_NUMBER_OF_BYTES_USED: -128
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CURRENT_NUMBER_OF_BYTES_USED: -128
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HIGH_NUMBER_OF_BYTES_USED: 0
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1 row in set (0,004 sec)
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MariaDB [performance_schema]> select t.*, m.* from memory_summary_by_thread_by_event_name m join threads t on m.thread_id = t.thread_id where current_number_of_bytes_used <0\G
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*************************** 1. row ***************************
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THREAD_ID: 1
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NAME: thread/sql/main
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TYPE: BACKGROUND
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PROCESSLIST_ID: NULL
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PROCESSLIST_USER: NULL
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PROCESSLIST_HOST: NULL
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PROCESSLIST_DB: mysql
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PROCESSLIST_COMMAND: NULL
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PROCESSLIST_TIME: 105
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PROCESSLIST_STATE: NULL
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PROCESSLIST_INFO: NULL
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PARENT_THREAD_ID: NULL
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ROLE: NULL
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INSTRUMENTED: YES
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HISTORY: YES
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CONNECTION_TYPE: Error
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THREAD_OS_ID: 14292
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THREAD_ID: 1
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EVENT_NAME: memory/sql/global_system_variables
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COUNT_ALLOC: 0
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COUNT_FREE: 2
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SUM_NUMBER_OF_BYTES_ALLOC: 0
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SUM_NUMBER_OF_BYTES_FREE: 128
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LOW_COUNT_USED: -2
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CURRENT_COUNT_USED: -2
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HIGH_COUNT_USED: 0
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LOW_NUMBER_OF_BYTES_USED: -128
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CURRENT_NUMBER_OF_BYTES_USED: -128
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HIGH_NUMBER_OF_BYTES_USED: 0
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1 row in set (0,003 sec)
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From the above we seem to see that something was freed twice and never allocated. This is either bug in memory instrumentation, or in the way server gets data from the summary tables, or we really freed some memory that was never allocated (and it may be a more serious bug). We should never see negative values in these tables.