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C.2.14. Latency is high: master:ONLINE, progress=41331580333, THL latency=78849.733

Last Updated: 2015-06-01

Condition or Error

Latency is high: master:ONLINE, progress=41331580333, THL latency=78849.733

Causes

  • There are many possible causes for this error, however, if you see the following within the log on the master it may indicate a specific issue:

    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.thl.CommitSeqnoTable.updateLastCommitSeqno(CommitSeqnoTable.java:548)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.thl.CatalogManager.updateCommitSeqnoTable(CatalogManager.java:223)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.thl.THL.updateCommitSeqno(THL.java:593)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.thl.THLStoreApplier.apply(THLStoreApplier.java:163)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.pipeline.SingleThreadStageTask.apply(SingleThreadStageTask.java:768)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.pipeline.SingleThreadStageTask.runTask(SingleThreadStageTask.java:501)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at com.continuent.tungsten.replicator.pipeline.SingleThreadStageTask.run(SingleThreadStageTask.java:176)
    INFO | jvm 1 | 2016/02/09 15:01:54 | at java.lang.Thread.run(Thread.java:745)
    INFO | jvm 1 | 2016/02/09 15:01:54 |

    The stack trace shows that the replicator is updating the trep_commit_seqno table which is normally a very fast operation.

    The underlying reason may either be:

    • It is possible that updates to MySQL are somehow getting delayed, which would slow down the operation of the replicator as it updates each status update.

    • Check the block commit size, as low values will increase the number of updates to the table, and if the MySQL server updates are slow, this in turn slows down the operation of the replicator.

Rectifications

  • Focus on making sure the IO system and MySQL commits are not being blocked.

    You can try increasing replicator.stage.q-to-thl.blockCommitRowCount so the replicator has less commits to MySQL on the master.

    You can continue to track progress through trepctl status -name tasks as you may see the appliedLastSeqno value updating less often if you increase this by a lot. Beware that increasing this value too much increases possible data loss since it creates less sync points with the slaves.