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  1. MariaDB Server
  2. MDEV-33067

SCN(Sequence Commit Number) based MVCC

Details

    • New Feature
    • Status: Stalled (View Workflow)
    • Critical
    • Resolution: Unresolved
    • 12.1
    • None

    Description

      SCN is a sequence number which was generated while committing transaction, and it should always be increased. With SCN, the snapshot for MVCC can only use a version number to compare with SCN.

      origin commit from zhai weixiang: https://bugs.mysql.com/bug.php?id=109599

      Attachments

        1. sbench
          2 kB
          Marko Mäkelä

        Issue Links

          is blocked by

          Task - A task that needs to be done. MDEV-33066 Tencent requested features

          • Critical - Crashes, loss of data, severe memory leak.
          • Open
          relates to

          Task - A task that needs to be done. MDEV-12288 Reset DB_TRX_ID when the history is removed, to speed up MVCC

          • Major - Major loss of function.
          • Closed

          Task - A task that needs to be done. MDEV-15104 Remove trx_sys_t::rw_trx_ids and trx_sys_t::serialisation_list

          • Major - Major loss of function.
          • Closed

          Task - A task that needs to be done. MDEV-15158 On commit, do not write to the TRX_SYS page

          • Major - Major loss of function.
          • Closed

          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-20630 lf_hash get performance regression since the bucket size won't decrease

          • Major - Major loss of function.
          • Confirmed

          Bug - A problem which impairs or prevents the functions of the product. MDEV-21423 lock-free trx_sys get performance regression cause by lf_find and ut_delay

          • Major - Major loss of function.
          • Stalled

          Bug - A problem which impairs or prevents the functions of the product. MDEV-35702 ReadViewBase::m_ids had better use an initial fixed part

          • Major - Major loss of function.
          • Open

          Activity

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            View 7 older comments
            marko Marko Mäkelä added a comment -

            I found out that there is a Sysbench option --secondary that will cause a secondary index to be created on the id column. With that, I got lower throughput as expected, but the innodb_use_scn=ON still benefited reads:

            revision oltp_update_non_index/tps oltp_point_select/tps
            11.0 baseline 90980.16 182791.50
            innodb_use_scn=ON 90643.05 213464.70

            As far as I understood, the file format changes affect undo logs and clustered index pages, not secondary indexes at all.

            marko Marko Mäkelä added a comment - I found out that there is a Sysbench option --secondary that will cause a secondary index to be created on the id column. With that, I got lower throughput as expected, but the innodb_use_scn=ON still benefited reads: revision oltp_update_non_index /tps oltp_point_select /tps 11.0 baseline 90980.16 182791.50 innodb_use_scn=ON 90643.05 213464.70 As far as I understood, the file format changes affect undo logs and clustered index pages, not secondary indexes at all.
            poempeng Yin Peng added a comment -

            Hello marko, thank you for your response. I think the main benefit of SCN is that it enhances the efficiency of readview creation and visibility checking, especially in read-write workloads. This benefit is not limited to primary index.

            poempeng Yin Peng added a comment - Hello marko, thank you for your response. I think the main benefit of SCN is that it enhances the efficiency of readview creation and visibility checking, especially in read-write workloads. This benefit is not limited to primary index.
            marko Marko Mäkelä added a comment -

            I think that it would be worth repeating the performance tests after the relatively simple performance tweak MDEV-35702 has been implemented.

            marko Marko Mäkelä added a comment - I think that it would be worth repeating the performance tests after the relatively simple performance tweak MDEV-35702 has been implemented.
            svoj Sergey Vojtovich added a comment -

            marko, there was no feedback to your review for over 2 months. We should either complete this PR ourselves or decline it. If you find this worthy, but not ready to allocate resources, we can close PR and keep MDEV open.

            svoj Sergey Vojtovich added a comment - marko , there was no feedback to your review for over 2 months. We should either complete this PR ourselves or decline it. If you find this worthy, but not ready to allocate resources, we can close PR and keep MDEV open.
            marko Marko Mäkelä added a comment -

            Let’s return to this after MDEV-35702 has been implemented.

            marko Marko Mäkelä added a comment - Let’s return to this after MDEV-35702 has been implemented.

            People

              marko Marko Mäkelä
              zhangyuan zhangyuan
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                Updated:

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