Uploaded image for project: 'Core Server'
  1. Core Server
  2. SERVER-10793

Start election if more than one primary is online

    XMLWordPrintable

    Details

    • Type: Improvement
    • Status: Closed
    • Priority: Major - P3
    • Resolution: Fixed
    • Affects Version/s: None
    • Fix Version/s: 2.4.10, 2.5.5
    • Component/s: Replication
    • Labels:
      None

      Description

      Issue Status as of March 28, 2014

      ISSUE SUMMARY
      Replica sets should only ever contain at most one primary node. If a primary detects another primary in the replica set via the heartbeat messages, the current behavior would force the primary to step down only if its _id in the replica set configuration is higher than the other primary's _id. The intention of this was to only step down one of the primaries, thus avoiding a new election. However, since the _id is chosen arbitrarily and does not indicate priority, this can lead to a lower-priority member remaining as the primary node. Another issue is a one-way network partition, which could potentially lead to multiple primary nodes for prolonged times.

      USER IMPACT
      This bug can lead to a primary node that does not have the highest priority, or in rare cases (i.e. with transient network issues) to multiple primaries for prolonged times. The latter situation can affect data integrity.

      SOLUTION
      The fix is to unconditionally step down all primary nodes if multiple primary nodes are detected. While this can cause elections in more cases than before, it is safer than having the wrong primary, or potentially multiple primaries.

      WORKAROUNDS
      In situations where a lower-priority node remains the primary, a forced election with rs.stepDown() can promote the higher-priority node back to primary.

      AFFECTED VERSIONS
      All versions from 2.2.0 to 2.4.9 are affected.

      PATCHES
      The fix is included in the 2.4.10 production release and the 2.5.5 development release, which will evolve into the 2.6.0 production release.

      Original Description

      Check at every heartbeat, as it comes in, that the state of the world shows only one primary at most. If more than one is found, start an election.

        Attachments

          Issue Links

            Activity

              People

              • Votes:
                0 Vote for this issue
                Watchers:
                6 Start watching this issue

                Dates

                • Created:
                  Updated:
                  Resolved: