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     <h4 class="title">
      <a name="group-replication-performance-xcom-cache-increase">
      </a>
      20.7.6.1 Increasing the cache size
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  <p>
   If a member is absent for a period that is not long enough for
        it to be expelled from the group, it can reconnect and start
        participating in the group again by retrieving missed
        transactions from another member's XCom message cache. However,
        if the transactions that happened during the member's absence
        have been deleted from the other members' XCom message caches
        because their maximum size limit was reached, the member cannot
        reconnect in this way.
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  <p>
   Group Replication's Group Communication System (GCS) alerts you,
        by a warning message, when a message that is likely to be needed
        for recovery by a member that is currently unreachable is
        removed from the message cache. This warning message is logged
        on all the active group members (only once for each unreachable
        member). Although the group members cannot know for sure what
        message was the last message seen by the unreachable member, the
        warning message indicates that the cache size might not be
        sufficient to support your chosen waiting period before a member
        is expelled.
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  <p>
   In this situation, consider increasing the
   <a class="link" href="group-replication-system-variables.html#sysvar_group_replication_message_cache_size">
    <code class="literal">
     group_replication_message_cache_size
    </code>
   </a>
   limit with reference to the expected volume of messages in the
        time period specified by the
   <a class="link" href="group-replication-system-variables.html#sysvar_group_replication_member_expel_timeout">
    <code class="literal">
     group_replication_member_expel_timeout
    </code>
   </a>
   system variable plus the 5-second detection period, so that the
        cache contains all the missed messages required for members to
        return successfully. You can also consider increasing the cache
        size limit temporarily if you expect a member to become
        unreachable for an unusual period of time.
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