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Il 25/11/2015 21:21, Jaime Crespo ha scritto:<br>
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<div>Always fearing doing queries on a lagged replica on labs?
Not anymore!<br>
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While Betacommand's tool [0] was very useful, it was also very
inaccurate, as it tried to check the lag by looking at the
last rows updated, which can be a lot of time on the least
popular wikis.<br>
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What I offer now is sub-second accurate lag measuring, by
writing on the production masters the current time, in
microseconds, every 0.5 seconds and making that available on all
hosts (using this tool [1]). So, it is more accurate than SHOW
SLAVE STATUS, because it compares the difference with the
original master, and it will work even if replication is broken.<br
clear="all">
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So even if the replicas don't get updated the heartbeat will report
them as up to date?<br>
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<div>To read it, just do SELECT * FROM
heartbeat_p.heartbeat;<br>
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<div>And you will get:<br>
+-------+----------------------------+------+<br>
| shard | last_updated | lag |<br>
+-------+----------------------------+------+<br>
| s6 | 2015-11-25T20:20:32.000980 | 0 |<br>
| s2 | 2015-11-25T20:20:32.001030 | 0 |<br>
| s7 | 2015-11-25T20:20:32.001070 | 0 |<br>
| s3 | 2015-11-25T20:20:32.001000 | 0 |<br>
| s4 | 2015-11-25T20:20:32.000920 | 0 |<br>
| s1 | 2015-11-25T20:20:32.000740 | 0 |<br>
| s5 | 2015-11-25T20:20:32.000830 | 0 |<br>
+-------+----------------------------+------+<br>
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<div><br>
Read the detailed documentation on: [2]<br>
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<div>Use it, create a web page if you want to make it
public! Report a ticket if it gets too high! Report a
ticket if you need more info (a record per wiki?). But I
wanted to give you the essentials, and you can build
yourselves on top of that.<br>
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<div>Only 2 know bugs:<br>
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<div>- There is microsecond accuracy, but it cannot be used
until a bug in MariaDB is fixed [3]<br>
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<div>- enwiki will only report s1 lag until that server is
restarted due to some existing filters. We will schedule
that at some time in the future.<br>
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<div><br>
[0]<<a moz-do-not-send="true"
href="http://tools.wmflabs.org/betacommand-dev/cgi-bin/replag">http://tools.wmflabs.org/betacommand-dev/cgi-bin/replag</a>><br>
[1]<<a moz-do-not-send="true"
href="https://www.percona.com/doc/percona-toolkit/2.2/pt-heartbeat.html">https://www.percona.com/doc/percona-toolkit/2.2/pt-heartbeat.html</a>><br>
[2]<<a moz-do-not-send="true"
href="https://wikitech.wikimedia.org/wiki/Help:Tool_Labs/Database#Identifying_lag">https://wikitech.wikimedia.org/wiki/Help:Tool_Labs/Database#Identifying_lag</a>><br>
[3]<<a moz-do-not-send="true"
href="https://mariadb.atlassian.net/browse/MDEV-9175">https://mariadb.atlassian.net/browse/MDEV-9175</a>><br>
-- <br>
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<div>Jaime Crespo<br>
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<<a moz-do-not-send="true"
href="http://wikimedia.org" target="_blank">http://wikimedia.org</a>><br>
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