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  1. MariaDB Server
  2. MDEV-30216

Read-ahead unnecessarily allocates and frees pages when a page is in the buffer pool

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    Description

      While testing MDEV-29986 and some other changes, wlad noted that the function buf_read_page_low() is allocating and freeing a block in buf_pool.LRU when the requested page exists in the buffer pool.

      The code has been refactored in 10.5 and 10.6, but this does not look like a regression: the logic always seems to have been like that.

      Thanks to the refactored buf_pool.page_hash in 10.5 (MDEV-22871) and the lock elision (MDEV-26769), it could be faster to perform extra lookups to avoid unnecessary allocation and some contention on buf_pool.mutex.

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          causes

          Bug - A problem which impairs or prevents the functions of the product. MDEV-30911 Multi-batch recovery of ROW_FORMAT=COMPRESSED table hangs

          • Blocker - Blocks development and/or testing work, production could not run.
          • Closed
          includes

          Bug - A problem which impairs or prevents the functions of the product. MDEV-26662 buf_read_page_background() is blocking on LRU eviction

          • Major - Major loss of function.
          • Closed
          relates to

          Task - A task that needs to be done. MDEV-29694 Remove the InnoDB change buffer

          • Blocker - Blocks development and/or testing work, production could not run.
          • Closed

          Activity

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            marko Marko Mäkelä created issue -
            marko Marko Mäkelä made changes -
            Field Original Value New Value
            Status Open [ 1 ] In Progress [ 3 ]
            marko Marko Mäkelä added a comment -

            This change is easier to implement after removing the InnoDB change buffer (MDEV-29694).

            marko Marko Mäkelä added a comment - This change is easier to implement after removing the InnoDB change buffer ( MDEV-29694 ).
            marko Marko Mäkelä made changes -
            marko Marko Mäkelä made changes -
            Fix Version/s 10.12 [ 28320 ]
            Fix Version/s 10.6 [ 24028 ]
            Fix Version/s 10.7 [ 24805 ]
            Fix Version/s 10.8 [ 26121 ]
            Fix Version/s 10.9 [ 26905 ]
            Fix Version/s 10.10 [ 27530 ]
            Fix Version/s 10.11 [ 27614 ]
            marko Marko Mäkelä added a comment -

            The additional buf_pool.page_hash lookups in my initial fix might cause some regression in the case when none of the pages that are submitted for read-ahead exist in the buffer pool. It could be revised further as follows:

            1. In buf_page_init_for_read(), do not invoke buf_LRU_get_free_block() but expect the caller to pass the block instead.
            2. If the page already existed in the buffer pool, the caller can reuse the placeholder block for a subsequent call. Else, a new block will be allocated.
            3. This could be combined with a fix of MDEV-26790.
            marko Marko Mäkelä added a comment - The additional buf_pool.page_hash lookups in my initial fix might cause some regression in the case when none of the pages that are submitted for read-ahead exist in the buffer pool. It could be revised further as follows: In buf_page_init_for_read() , do not invoke buf_LRU_get_free_block() but expect the caller to pass the block instead. If the page already existed in the buffer pool, the caller can reuse the placeholder block for a subsequent call. Else, a new block will be allocated. This could be combined with a fix of MDEV-26790 .
            mleich Matthias Leich added a comment -

            origin/bb-10.11-MDEV-30216-MDEV-26790 c85c38683af18c5851afa5382aa7aaf869536176 2023-01-13T16:46:20+02:00
            performed well in RQG testing. Bad effects observed were in the main trees too.

            mleich Matthias Leich added a comment - origin/bb-10.11- MDEV-30216 - MDEV-26790 c85c38683af18c5851afa5382aa7aaf869536176 2023-01-13T16:46:20+02:00 performed well in RQG testing. Bad effects observed were in the main trees too.
            marko Marko Mäkelä made changes -
            Fix Version/s 11.0.1 [ 28548 ]
            Fix Version/s 11.0 [ 28320 ]
            Resolution Fixed [ 1 ]
            Status In Progress [ 3 ] Closed [ 6 ]
            thiru Thirunarayanan Balathandayuthapani made changes -
            thiru Thirunarayanan Balathandayuthapani made changes -
            marko Marko Mäkelä made changes -
            marko Marko Mäkelä made changes -

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              marko Marko Mäkelä
              marko Marko Mäkelä
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                Updated:
                Resolved:

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