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https://issues.apache.org/jira/browse/CASSANDRA-11427?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15253550#comment-15253550
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Stefan Podkowinski commented on CASSANDRA-11427:
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bq. this only concerns partition and range tombstones, so this is imo a fairly
minor efficiency problem, not a correction issue.
Although the performance overhead implied by this bug should be fairly low in
most cases, it's leaving people confused why these read repairs happen in first
place. If you have some monitoring in place telling you the system constantly
has to read repair data, you should get to investigate. That's what I did.
bq. So that I wonder if it's worth taking any risk just for 2.2.
Any tests I can add to reduce the risks of possible side effects?
> Range slice queries CL > ONE trigger read-repair of purgeable tombstones
> ------------------------------------------------------------------------
>
> Key: CASSANDRA-11427
> URL: https://issues.apache.org/jira/browse/CASSANDRA-11427
> Project: Cassandra
> Issue Type: Bug
> Reporter: Stefan Podkowinski
> Assignee: Stefan Podkowinski
> Priority: Minor
> Fix For: 2.1.x, 2.2.x
>
> Attachments: 11427-2.1.patch, 11427-2.2_v2.patch
>
>
> Range queries will trigger read repairs for purgeable tombstones on hosts
> that already compacted given tombstones. Clusters with periodical jobs for
> scanning data ranges will likely see tombstones ressurected through RRs just
> to have them compacted again later at the destination host.
> Executing range queries (e.g. for reading token ranges) will compare the
> actual data instead of using digests when executed with CL > ONE. Responses
> will be consolidated by {{RangeSliceResponseResolver.Reducer}}, where the
> result of {{RowDataResolver.resolveSuperset}} is used as the reference
> version for the results. {{RowDataResolver.scheduleRepairs}} will then send
> the superset to all nodes that returned a different result before.
> Unfortunately this does also involve cases where the superset is just made up
> of purgeable tombstone(s) that already have been compacted on the other
> nodes. In this case a read-repair will be triggered for transfering the
> purgeable tombstones to all other nodes nodes that returned an empty result.
> The issue can be reproduced with the provided dtest or manually using the
> following steps:
> {noformat}
> create keyspace test1 with replication = { 'class' : 'SimpleStrategy',
> 'replication_factor' : 2 };
> use test1;
> create table test1 ( a text, b text, primary key(a, b) ) WITH compaction =
> {'class': 'SizeTieredCompactionStrategy', 'enabled': 'false'} AND
> dclocal_read_repair_chance = 0 AND gc_grace_seconds = 0;
> delete from test1 where a = 'a';
> {noformat}
> {noformat}
> ccm flush;
> ccm node2 compact;
> {noformat}
> {noformat}
> use test1;
> consistency all;
> tracing on;
> select * from test1;
> {noformat}
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