[
https://issues.apache.org/jira/browse/CASSANDRA-6887?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14012319#comment-14012319
]
Sylvain Lebresne commented on CASSANDRA-6887:
---------------------------------------------
I don't think that patch is what we want to do. We have
dclocal_read_repair_chance exactly for that kind of reasons. If you don't want
to get any digest sent to a remote DC, then you should set read_repair_chance
to 0 and configure dclocal_read_repair to whatever you want. Maybe that's
something that needs documenting, and in fact I'd be in favor of making it a
default (i.e instead of having read_repair_chance=0.1 and
dclocal_read_repair_chance=0, to switch to read_repair_chance=0 and
dclocal_read_repair_chance=0.1. If you have only one DC, then it won't change
from the current default, and if you have multiple-DC, I can agree that not
crossing DC boundaries for read repair is a better default. But I'm not in
favor of removing the option altogether).
That said, the behaviour described above does sound like a bug. Since by
default read_repair_chance is 0.1, there should be cross-DC digest queries
every 10 queries or so, and those *should* repair. If that's not the case, we
should fix it.
> LOCAL_ONE read repair only does local repair, in spite of global digest
> queries
> -------------------------------------------------------------------------------
>
> Key: CASSANDRA-6887
> URL: https://issues.apache.org/jira/browse/CASSANDRA-6887
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Environment: Cassandra 2.0.6, x86-64 ubuntu precise
> Reporter: Duncan Sands
> Assignee: Aleksey Yeschenko
> Fix For: 2.0.9, 2.1 rc1
>
> Attachments: 6887-2.0.txt
>
>
> I have a cluster spanning two data centres. Almost all of the writing (and a
> lot of reading) is done in DC1. DC2 is used for running the occasional
> analytics query. Reads in both data centres use LOCAL_ONE. Read repair
> settings are set to the defaults on all column families.
> I had a long network outage between the data centres; it lasted longer than
> the hints window, so after it was over DC2 didn't have the latest
> information. Even after reading data many many times in DC2, the returned
> data was still out of date: read repair was not correcting it.
> I then investigated using cqlsh in DC2, with tracing on.
> What I saw was:
> - with consistency ONE, after about 10 read requests a digest request would
> be sent to many nodes (spanning both data centres), and the data in DC2 would
> be repaired.
> - with consistency LOCAL_ONE, after about 10 read requests a digest request
> would be sent to many nodes (spanning both data centres), but the data in DC2
> would not be repaired. This is in spite of digest requests being sent to
> DC1, as shown by the tracing.
> So it looks like digest requests are being sent to both data centres, but
> replies from outside the local data centre are ignored when using LOCAL_ONE.
> The same data is being queried all the time in DC1 with consistency
> LOCAL_ONE, but this didn't result in the data in DC2 being read repaired
> either. This is a slightly different case to what I described above: in that
> case the local node was out of date and the remote node had the latest data,
> while here it is the other way round.
> It could be argued that you don't want cross data centre read repair when
> using LOCAL_ONE. But then why bother sending cross data centre digest
> requests? And if only doing local read repair is how it is supposed to work
> then it would be good to document this somewhere.
--
This message was sent by Atlassian JIRA
(v6.2#6252)
