Thanks for reporting this.
Pine
On Aug 26, 2015 1:27 PM, "Andrew Otto" <aotto(a)wikimedia.org> wrote:
Hi all,
Now that we’ve had a little space to analyze the problem, I wanted to call
out a recent webrequest data loss issue that we experienced on two separate
occasions.
We attempted to upgrade to Kafka 0.8.2.1, and it wasn’t until the second
attempt that we actually found the problem. Kafka 0.8.2.1 ships with a
buggy version of Snappy[1] that causes messages to not be compressed
properly. This caused a ~4x increase network and disk I/O around the
cluster all at once.
We’ve documented the incidents and the occasions of significant data loss
here:
https://wikitech.wikimedia.org/wiki/Incident_documentation/20150803-Kafka
https://wikitech.wikimedia.org/wiki/Incident_documentation/20150810-Kafka#C…
https://wikitech.wikimedia.org/wiki/Analytics/Data/Webrequest
This loss will affect the output of pagecount* and pageview datasets, as
well as other webrequest generated statistics. Please consider statistics
that are generated from webrequest data using the following UTC hours
unreliable:
2015-08-03T18:00 - 2015-08-03T23:00
2015-08-10T15:00 - 2015-08-10T21:00
2015-08-11T17:00 - 2015-08-11T18:00
Many apologies for any inconvenience this causes. We’ve learned a lot
during this turmoil, and have a lot of ideas on how to hopefully prevent
this from happening in the future, and also how to reduce loss and
complexity if and when it does. The analytics engineering team will be
doing a post mortem on this soon, in which we will document these ideas.
Thanks,
-Andrew Otto
[1]
https://issues.apache.org/jira/browse/KAFKA-2189
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