Uploaded image for project: 'MariaDB Server'
  1. MariaDB Server
  2. MDEV-8112

PATCH: no slave left behind



    • Task
    • Status: Stalled (View Workflow)
    • Major
    • Resolution: Unresolved
    • 11.7
    • None
    • None


      patch has been ported to 10.1
      you can use it under new (also called "3-clause") BSD license
      i have done internal benchmarks...but you are most welcome to do some too.

      no slave left behind

      this patch implements master throttling based on slave lag,
      aka no slave left behind. the core feature works as follows
      1) the semi-sync-reply is ammended to also report back SQL-thread
      position (aka exec position)
      2) transactions are not removed from the "active-transaction-list"
      in the semi-sync-master plugin until atleast one slave has reported
      that it has executed this transaction. the slave lag can then
      be estimated by calculating how long the oldest transaction has been
      lingering in the active-transaction-list.
      3) client-threads are forced to wait before commit until slave lag
      has decreased to acceptable value.

      the following variables are introduced on master:

      • rpl_semi_sync_master_max_slave_lag (global)
      • rpl_semi_sync_master_slave_lag_wait_timeout (session)

      the following status variables are introduced on master:

      • rpl_semi_sync_master_slave_lag_wait_sessions
      • rpl_semi_sync_master_estimated_slave_lag
      • rpl_semi_sync_master_trx_slave_lag_wait_time
      • rpl_semi_sync_master_trx_slave_lag_wait_num
      • rpl_semi_sync_master_avg_trx_slave_lag_wait_time

      the following variables are introduced on slave:

      • rpl_semi_sync_slave_lag_enabled (global)

      in addition to this, 2 optimizations that decreases overhead of semi-sync
      is introduced.
      1) the idea of this is that if when a slave should send and transaction,
      it checks if it should be semi-synced, but rather
      than semi-sync:ing each transaction (which is done currently) the code
      will skip semi-syncing transaction if there already is newer transactions
      committed. But, since this can mean that semi-syncing is delayed indefinitely
      a cap is set using 2 new master variables:

      • rpl_semi_sync_master_max_unacked_event_bytes (global)
      • rpl_semi_sync_master_max_unacked_event_count (global)
        2) rpl_semi_sync_master_group_commit which makes the semi-sync
        plugin only semi-sync the last transaction in a group commit.


        Issue Links



              bnestere Brandon Nesterenko
              jonaso Jonas Oreland
              6 Vote for this issue
              19 Start watching this issue



                Git Integration

                  Error rendering 'com.xiplink.jira.git.jira_git_plugin:git-issue-webpanel'. Please contact your Jira administrators.