Details

    • Type: Task
    • Status: Closed
    • Priority: Major
    • Resolution: Fixed
    • Fix Version/s: 10.0.0
    • Component/s: None
    • Labels:

      Description

      This task is about implementing a way for a MariaDB replication slave to
      replicate from more than one master simultaneously.

      Each master is handled by a specific replicator instance in the slave
      server. Each replicator instance consists of separate I/O thread, SQL thread,
      and associated state and configuration. In efffect, several replication slaves
      are running at the same time, each replicating from a separate master, but all
      replicating into a common data store (typically, but not necessarily to
      separate databases/tables).

      A replicator instance is identified with a user-chosen name used in
      replication SQL statements such as CHANGE MASTER TO ...
      This name is also included in file names to distinguish the files that keep
      the replication state (relay logs, master.info, relay-log.info). This way,
      each separate instance can be configured separately, but otherwise the same
      way as existing single-source replication.

      In order to remain backwards-compatible with existing third-party scripts
      etc., the replicator instance name is made optional in all existing
      replication statements. If it is omitted, the name "default" is used, and for
      this particular name, master.info and the other files retain their old names
      to allow seamless upgrades of slaves.

      In this worklog, there is no extra conflict resolution proposed. The effect of
      updates from one master on replication from another master will be the same as
      the effect of direct user SQL queries on the slave server, ie. it is the
      responsibility of the user/DBA to ensure no conflicts occur. If a conflict
      causes replication of an event to fail (with duplicate key violation eg.), the
      corresponding slave SQL thread will stop, requiring manual intervention to fix
      and start.

      An easy and typical way to avoid conflicts would be to eg. to use separate
      databases for each master->slave replication channel. RBR idempotent slave
      application can also be used to help resolve conflicts, for example.

      See also MySQL WL#1697: http://forge.mysql.com/worklog/task.php?id=1697

      High-Level Specification

      Here is a preliminary list of things that need to be changed/extended to
      handle multi-source:

      File names
      ----------

      These files used to store replication state must be extended to include the
      replicator instance name. For "default", as a special case, the old name
      should be used for backwards compatibility:

      HOST-relay-bin.XXXXXX
      HOST-relay-bin.index
      relay-log.info
      master.info

      SQL statements
      --------------

      These statements need to be extended to take an optional replicator instance
      name. If omitted, "default" is used:

      CHANGE MASTER TO
      LOAD DATA FROM MASTER
      LOAD TABLE xxx FROM MASTER
      MASTER_POS_WAIT(file, position, timeout)
      RESET SLAVE
      SHOW SLAVE STATUS
      START SLAVE
      START SLAVE UNTIL ...
      STOP SLAVE

      System variables
      ----------------

      These system variables need to handle multiple replicator instances. Some can
      remain global, and apply to all instances. Some will need to be per-instance,
      and can probably use structured system variables, same was as for multiple key
      caches:

      SQL_SLAVE_SKIP_COUNTER
      log_slave_updates
      master_connect_retry
      master_info_file
      master_retry_count
      max_relay_log_size
      read_only
      relay_log
      relay_log_index
      relay_log_info_file
      relay_log_purge
      relay_log_space_limit
      replicate_do_db
      replicate_do_table
      replicate_ignore_db
      replicate_ignore_table
      replicate_rewrite_db
      replicate_same_server_id
      replicate_wild_do_table
      replicate_wild_ignore_table
      report_host
      report_port
      skip_slave_start
      slave_compressed_protocol
      slave_load_tmpdir
      slave_net_timeout
      slave_skip_errors

      The deprecated options master_host, master_port, master_user, master_password,
      and master_ssl_* should not be supported for multi source replication.

      Low-Level Design

      A main part of this worklog will be to modify the server code so that all
      slave objects and data can have multiple instances, not use global variables,
      etc. And so that all user-visible interfaces (SQL statements, system
      variables, status variables, files) are extended to support multiple
      replicator instances.

      Another major part is to carefully develop the feature and not the least test
      it for full backwards compatibility in the case where only a single, default
      master is used. If this is not done correctly, a lot of users will get
      problems when slaves are upgraded and their monitoring scripts, management
      scripts, or replication state breaks.

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            • Assignee:
              monty Michael Widenius
              Reporter:
              ratzpo Rasmus Johansson
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              Dates

              • Created:
                Updated:
                Resolved:

                Time Tracking

                Estimated:
                Original Estimate - 9 weeks, 4 hours Original Estimate - 9 weeks, 4 hours
                9w 4h
                Remaining:
                Time Spent - 4 weeks, 4 days, 4 hours, 50 minutes Remaining Estimate - 4 weeks, 1 day
                4w 1d
                Logged:
                Time Spent - 4 weeks, 4 days, 4 hours, 50 minutes Remaining Estimate - 4 weeks, 1 day
                4w 4d 4h 50m