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  1. MariaDB MaxScale
  2. MXS-4669

Make transaction_replay work better in read-only scenarios



    • New Feature
    • Status: Open (View Workflow)
    • Minor
    • Resolution: Unresolved
    • 23.02.2
    • Icebox
    • readwritesplit
    • None
    • CentOS, MaxScale



      When readwritesplit is used with a servers that are all labeled Slave, transaction_replay will cause slow failures in cases where it is known that no replacement will ever arrive. For these cases, an additional flag that tells readwritesplit to fail immediately if a write is seen but all servers are currently Slave. This would improve how readwritesplit works in these kinds of use-cases.


      The case where a write is received but no target was found can be handled in RWSplitSession::handle_routing_failure(). In this function, all attempts at retrying of both individual statements and complete transactions can be disabled if the query is a write and no candidate is available.

      This could also be implemented as a read-only mode in readwritesplit where a write will immediately cause the connection to be closed. This could be done in RWSplitSession::route_query() by checking what the target type of the query is. If the target type is TARGET_MASTER, the connection can be immediately closed. An improvement to this would be to queue a read-only error to be sent to the client. This functionality needd to generate the errors already exists for the master_failure_mode=error_on_write mode.

      Original description:

      The customer is requesting to add the "transaction_replay" feature to the "readconnroute" router. This would allow for transparent node failures / fail-overs between only the slaves for maxscale configuration where only "slaves with external master" and no "master" are being part of maxscale server. (as per example below)

      Server │ Address │ Port │ Connections │ State │ GTID
      repl2 │ │ 3306 │ Running, Slave of External Server │ 0-1-57233
      repl3 │ │ 3306 │ Running, Slave of External Server │ 0-1-57233




            Unassigned Unassigned
            martin.reinhardt@mariadb.com Martin Reinhardt
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