how wsrep_flow_control_paused_ns works?

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4 comments

  • Official comment
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    Krzysztof Ksiazek

    Hi,

    First of all, wsrep_flow_control_paused_ns is not a replication delay. It tells you for how long time the replication has to be stopped due to some nodes having troubles in catching up. You may have zero flow control but replication delay will still be there. Typically, for small transactions, it's not noticeable but it does exist.

    There's no need for flushing tables. It has no effect over the wsrep_flow_control_paused_ns. Why it behaved like in your tests, it is not possible to tell without knowing the full context and how all the metrics changed. Such spike might have been triggered by some external activity. Filesystem cache flush, InnoDB redo log flush, some network performance problems. Basically, anything. You need to do a full investigation in a system which you have instrumentation for at least majority of MySQL and host level metrics to have a hope of understanding why it behaved like that.

    Thanks,
    Krzysztof

  • Avatar
    jasmine

    Hi!

    Thankyou for your answer

    So, i just do a simple test again by inserting 1500 data rows for 5 times. Here is the time in nanosecond.

    I noticed that the time is getting higher. Is it possible to get the lower time after inserting data several times?

     

  • Avatar
    Krzysztof Ksiazek

    Hi,

    MySQL treats its metrics as either counters or gauges (at least I don't remember any other option from the top of my head). Gauge (such as, for example, Threads_connected) shows the state of the metric at the given time. Counter, on the other hand (just like wsrep_flow_control_paused_ns is) is always increasing. To tell how it changed, you have to calculate the delta between previous measurement and the last one. This will tell you how the counter changed in the meantime. I hope this helps.

    Thanks,
    Krzysztof

  • Avatar
    jasmine

    Thankyou so much Krzysztof, it's really helpful :)

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