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Re: Refresh slave state




2015-06-19 12:08 GMT+02:00 Ben RUBSON <ben.rubson@xxxxxxxxx>:
>
> 2015-06-18 22:52 GMT+02:00 shawn l.green <shawn.l.green@xxxxxxxxxx>:
>>
>> On 6/18/2015 2:10 PM, Ben RUBSON wrote:
>>>
>>> Hello,
>>>
>>> In order for the slave to quickly show a communication issue between
>>> the master and the slave, I set slave_net_timeout to 10.
>>> "show slave status" then quickly updates, perfect.
>>>
>>> I would also like the master to quickly show when the slave is no more
>>> reachable.
>>>
>>> However, "show processlist" and "show slave hosts" take a very long
>>> time to update their status when the slave has gone.
>>> Is there any way to have a refresh rate of about 10 seconds, as I did
>>> on slave side ?
>>
>> There are two situations to consider
>>
>> 1) The slave is busy re-trying.  It will do this a number of times then
>> eventually disconnect itself. If it does disconnect itself, the processlist
>> report will show it as soon as that happens.
>
> Yes, I confirm.
>
>> 2) The connection between the master and slave died (or the slave itself is
>> lost).  In this case, the server did not receive any "I am going to
>> disconnect" message from its client (the slave). So as far as the server is
>> concerned, it is simply sitting in a wait expecting the client to eventually
>> send in a new command packet.
>>
>> That wait is controlled by --wait-timeout.  Once an idle client connection
>> hits that limit, the server is programmed to think "the idiot on the other
>> end of this call has hung up on me" so it simply closes its end of the
>> socket. There are actually two different timers that could be used,
>> --wait-timeout or --interactive-timeout and which one is used to monitor the
>> idle socket depends entirely on if the client did or did not set the
>> 'interactive flag' when it formed the connection. MySQL slaves do not use
>> that flag.
>>
>> Now, if the line between the two systems died in the middle of a
>> conversation (an actual data transfer) then a shorter -net-write-timeout or
>> --net-read-timeout would expire and the session would die then.
>
> This is the interesting part yes, when the connection dies (whatever
> the link status is at this moment, idle or not).
> So I set wait_timeout=10.
>
> When the link is up, we clearly see that the idle connection is reset
> every 10 seconds : the "show processlist" clearly shows that the slave
> TCP source port changes, and time is reset from 10 to 0.
> Perfect.

Well this behavior is due to slave_net_timeout, not to wait_timeout.
So neither wait_timeout nor interactive_timeout (expected),
net_read_timeout, net_write_timeout helped.

> However, when the link dies, the "Binlog Dump" process stays in the
> "show processlist", I have to wait more than 1000 seconds for it to
> disappear.
> I made tests adding interactive_timeout=10, net_read_timeout=10 and
> net_write_timeout=10, however the behavior is the same.
>
> Did I miss something ?
>
> Of course goal is to monitor replication, from the slave (done and
> working thanks to slave_net_timeout), but from the master too (some
> more tuning needed), as we never know which one will be able to
> transmit the alert properly.
>
> Thank you very much Shawn.

Thank you again,

Best regards,

Ben

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