Patch: userstatsv2

This patch adds several INFORMATION_SCHEMA tables, several FLUSH and SHOW commands, and the userstat_running variable. These tables and commands can be used to understand the server activity better and identify the source of the load.

The functionality is disabled by default, and must be enabled by setting the userstat_running variable to ON. It works by keeping several hash tables in memory. To avoid contention over global mutexes, each connection has its own local statistics, which are occasionally merged into the global statistics, and the local statistics are then reset to 0.

This patch provides the following variables:

Enables or disables collection of statistics. The default is OFF, meaning no statistics are gathered. This is to ensure that the statistics collection doesn't cause any extra load on the server unless desired.

The patch provides the following INFORMATION_SCHEMA tables:

This table holds statistics about client connections. The Percona version of the patch restricts this table's visibility to users who have the SUPER or PROCESS privilege.

mysql> SELECT * FROM INFORMATION_SCHEMA.CLIENT_STATISTICS\G
*************************** 1. row ***************************
                CLIENT: 10.1.12.30
     TOTAL_CONNECTIONS: 20
CONCURRENT_CONNECTIONS: 0
        CONNECTED_TIME: 0
             BUSY_TIME: 93
              CPU_TIME: 48
        BYTES_RECEIVED: 5031
            BYTES_SENT: 276926
  BINLOG_BYTES_WRITTEN: 217
          ROWS_FETCHED: 81
          ROWS_UPDATED: 0
       TABLE_ROWS_READ: 52836023
       SELECT_COMMANDS: 26
       UPDATE_COMMANDS: 1
        OTHER_COMMANDS: 145
   COMMIT_TRANSACTIONS: 1
 ROLLBACK_TRANSACTIONS: 0
    DENIED_CONNECTIONS: 0
      LOST_CONNECTIONS: 0
         ACCESS_DENIED: 0
         EMPTY_QUERIES: 0

This table shows statistics on index usage. An older version of the patch contained a single column that had the TABLE_SCHEMA, TABLE_NAME and INDEX_NAME columns concatenated together. The Percona version of the patch separates these into three columns. Users can see entries only for tables to which they have SELECT access.

This table makes it possible to do many things that were difficult or impossible previously. For example, you can use it to find unused indexes and generate DROP commands to remove them.

mysql> SELECT * FROM INFORMATION_SCHEMA.INDEX_STATISTICS
   WHERE TABLE_NAME='tables_priv';
+--------------+-----------------------+--------------------+-----------+
| TABLE_SCHEMA | TABLE_NAME            | INDEX_NAME         | ROWS_READ |
+--------------+-----------------------+--------------------+-----------+
| mysql        | tables_priv           | PRIMARY            |         2 |
+--------------+-----------------------+--------------------+-----------+

This table is similar in function to the INDEX_STATISTICS table.

mysql> SELECT * FROM INFORMATION_SCHEMA.TABLE_STATISTICS
   WHERE TABLE_NAME='tables_priv';
+--------------+-------------------------------+-----------+--------------+------------------------+
| TABLE_SCHEMA | TABLE_NAME                    | ROWS_READ | ROWS_CHANGED | ROWS_CHANGED_X_INDEXES |
+--------------+-------------------------------+-----------+--------------+------------------------+
| mysql        | tables_priv                   |         2 |            0 |                      0 | 
+--------------+-------------------------------+-----------+--------------+------------------------+

This table contains information about user activity. The Percona version of the patch restricts this table's visibility to users who have the SUPER or PROCESS privilege.

The table gives answers to questions such as which users cause the most load, and whether any users are being abusive. It also lets you measure how close to capacity the server may be. For example, you can use it to find out whether replication is likely to start falling behind.

mysql> SELECT * FROM INFORMATION_SCHEMA.USER_STATISTICS\G
*************************** 1. row ***************************
                  USER: root
     TOTAL_CONNECTIONS: 5592
CONCURRENT_CONNECTIONS: 0
        CONNECTED_TIME: 6844
             BUSY_TIME: 179
              CPU_TIME: 72
        BYTES_RECEIVED: 603344
            BYTES_SENT: 15663832
  BINLOG_BYTES_WRITTEN: 217
          ROWS_FETCHED: 9793
          ROWS_UPDATED: 0
       TABLE_ROWS_READ: 52836023
       SELECT_COMMANDS: 9701
       UPDATE_COMMANDS: 1
        OTHER_COMMANDS: 2614
   COMMIT_TRANSACTIONS: 1
 ROLLBACK_TRANSACTIONS: 0
    DENIED_CONNECTIONS: 0
      LOST_CONNECTIONS: 0
         ACCESS_DENIED: 0
         EMPTY_QUERIES: 0

This patch provides the following commands:

These commands discard the specified type of stored statistical information.

These commands are another way to display the information you can get from the INFORMATION_SCHEMA tables. The commands accept WHERE clauses. They also accept but ignore LIKE clauses.

This patch actually contains functionality to flush/rotate the slow query log as well. This should be moved to the slow-query-log patch.