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MySQL 8.4 Reference Manual  /  ...  /  The INFORMATION_SCHEMA INNODB_CMPMEM and INNODB_CMPMEM_RESET Tables

28.4.7 The INFORMATION_SCHEMA INNODB_CMPMEM and INNODB_CMPMEM_RESET Tables

The INNODB_CMPMEM and INNODB_CMPMEM_RESET tables provide status information on compressed pages within the InnoDB buffer pool.

The INNODB_CMPMEM and INNODB_CMPMEM_RESET tables have these columns:

  • PAGE_SIZE

    The block size in bytes. Each record of this table describes blocks of this size.

  • BUFFER_POOL_INSTANCE

    A unique identifier for the buffer pool instance.

  • PAGES_USED

    The number of blocks of size PAGE_SIZE that are currently in use.

  • PAGES_FREE

    The number of blocks of size PAGE_SIZE that are currently available for allocation. This column shows the external fragmentation in the memory pool. Ideally, these numbers should be at most 1.

  • RELOCATION_OPS

    The number of times a block of size PAGE_SIZE has been relocated. The buddy system can relocate the allocated buddy neighbor of a freed block when it tries to form a bigger freed block. Reading from the INNODB_CMPMEM_RESET table resets this count.

  • RELOCATION_TIME

    The total time in microseconds used for relocating blocks of size PAGE_SIZE. Reading from the table INNODB_CMPMEM_RESET resets this count.

Example

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mysql> SELECT * FROM INFORMATION_SCHEMA.INNODB_CMPMEM\G *************************** 1. row *************************** page_size: 1024 buffer_pool_instance: 0 pages_used: 0 pages_free: 0 relocation_ops: 0 relocation_time: 0 *************************** 2. row *************************** page_size: 2048 buffer_pool_instance: 0 pages_used: 0 pages_free: 0 relocation_ops: 0 relocation_time: 0 *************************** 3. row *************************** page_size: 4096 buffer_pool_instance: 0 pages_used: 0 pages_free: 0 relocation_ops: 0 relocation_time: 0 *************************** 4. row *************************** page_size: 8192 buffer_pool_instance: 0 pages_used: 7673 pages_free: 15 relocation_ops: 4638 relocation_time: 0 *************************** 5. row *************************** page_size: 16384 buffer_pool_instance: 0 pages_used: 0 pages_free: 0 relocation_ops: 0 relocation_time: 0

Notes