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https://issues.apache.org/jira/browse/CASSANDRA-2870?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Jonathan Ellis updated CASSANDRA-2870:
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Attachment: 2870.txt
patch extracts the "give me the minimum set of endpoints necessary" code into
preferredEndpoints(), and makes it DC-aware for LOCAL_QUORUM reads.
> dynamic snitch + read repair off can cause LOCAL_QUORUM reads to return
> spurious UnavailableException
> -----------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-2870
> URL: https://issues.apache.org/jira/browse/CASSANDRA-2870
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 0.7.0
> Reporter: Jonathan Ellis
> Assignee: Jonathan Ellis
> Priority: Minor
> Fix For: 0.7.8, 0.8.2
>
> Attachments: 2870.txt
>
>
> When Read Repair is off, we want to avoid doing requests to more nodes than
> necessary to satisfy the ConsistencyLevel. ReadCallback does this here:
> {code}
> this.endpoints = repair || resolver instanceof RowRepairResolver
> ? endpoints
> : endpoints.subList(0, Math.min(endpoints.size(),
> blockfor)); // min so as to not throw exception until assureSufficient is
> called
> {code}
> You can see that it is assuming that the "endpoints" list is sorted in order
> of preferred-ness for the read.
> Then the LOCAL_QUORUM code in DatacenterReadCallback checks to see if we have
> enough nodes to do the read:
> {code}
> int localEndpoints = 0;
> for (InetAddress endpoint : endpoints)
> {
> if (localdc.equals(snitch.getDatacenter(endpoint)))
> localEndpoints++;
> }
> if (localEndpoints < blockfor)
> throw new UnavailableException();
> {code}
> So if repair is off (so we truncate our endpoints list) AND dynamic snitch
> has decided that nodes in another DC are to be preferred over local ones,
> we'll throw UE even if all the replicas are healthy.
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