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  1. MariaDB Server
  2. MDEV-31589

Secondary index MVCC access is unnecessarily inefficient

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      As noted in MDEV-31558, a covering secondary index read in InnoDB would look up the clustered index record twice and retrieve the matching version. In the test innodb.mvcc_secondary we have a table with 2 versions of 1 row, and the first SELECT statement would construct the old version of the clustered index not once, but twice.

      MDEV-20301 replaced row_sel_get_clust_rec_for_mysql() with Row_sel_get_clust_rec_for_mysql::operator(), which adds some caching. It missed an opportunity to remove the call row_sel_sec_rec_is_for_clust_rec() and to perform those checks as part of the loop that invokes row_sel_build_prev_vers_for_mysql().

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. MDEV-32286 ANALYZE displays a huge number of InnoDB secondary index pages_accessed

          • Critical - Crashes, loss of data, severe memory leak.
          • Confirmed

          New Feature - A new feature of the product, which has yet to be developed. MDEV-17598 InnoDB index option for per-record transaction ID

          • Major - Major loss of function.
          • Open

          Bug - A problem which impairs or prevents the functions of the product. MDEV-20301 InnoDB's MVCC has O(N^2) behaviors

          • Major - Major loss of function.
          • Closed

          Task - A task that needs to be done. MDEV-31558 Add InnoDB engine information to the slow query log

          • Critical - Crashes, loss of data, severe memory leak.
          • Closed

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              vlad.lesin Vladislav Lesin
              marko Marko Mäkelä
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