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https://issues.apache.org/jira/browse/CASSANDRA-3843?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Jonathan Ellis updated CASSANDRA-3843:
--------------------------------------
Attachment: 3843.txt
The null version was added for CASSANDRA-2680. I think the core problem here
is that the RSRR is being created with *all* the replica endpoints
({{liveEndpoints}}), not just the ones being asked to respond to the query
({{handler.endpoints}}). This is a bit tricky since the handler wants to know
its resolver at creation time, and unlike RowDigestResolver, RSRR wants to
initialize its endpoints at creation time too. Kind of hackish patch attached.
> Unnecessary ReadRepair request during RangeScan
> ------------------------------------------------
>
> Key: CASSANDRA-3843
> URL: https://issues.apache.org/jira/browse/CASSANDRA-3843
> Project: Cassandra
> Issue Type: Bug
> Components: Core
> Affects Versions: 1.0.0
> Reporter: Philip Andronov
> Assignee: Jonathan Ellis
> Fix For: 1.0.8
>
> Attachments: 3843.txt
>
>
> During reading with Quorum level and replication factor greater then 2,
> Cassandra sends at least one ReadRepair, even if there is no need to do that.
> With the fact that read requests await until ReadRepair will finish it slows
> down requsts a lot, up to the Timeout :(
> It seems that the problem has been introduced by the CASSANDRA-2494,
> unfortunately I have no enought knowledge of Cassandra internals to fix the
> problem and do not broke CASSANDRA-2494 functionality, so my report without a
> patch.
> Code explanations:
> {code:title=RangeSliceResponseResolver.java|borderStyle=solid}
> class RangeSliceResponseResolver {
> // ....
> private class Reducer extends
> MergeIterator.Reducer<Pair<Row,InetAddress>, Row>
> {
> // ....
> protected Row getReduced()
> {
> ColumnFamily resolved = versions.size() > 1
> ?
> RowRepairResolver.resolveSuperset(versions)
> : versions.get(0);
> if (versions.size() < sources.size())
> {
> for (InetAddress source : sources)
> {
> if (!versionSources.contains(source))
> {
>
> // [PA] Here we are adding null ColumnFamily.
> // later it will be compared with the "desired"
> // version and will give us "fake" difference which
> // forces Cassandra to send ReadRepair to a given
> source
> versions.add(null);
> versionSources.add(source);
> }
> }
> }
> // ....
> if (resolved != null)
>
> repairResults.addAll(RowRepairResolver.scheduleRepairs(resolved, table, key,
> versions, versionSources));
> // ....
> }
> }
> }
> {code}
> {code:title=RowRepairResolver.java|borderStyle=solid}
> public class RowRepairResolver extends AbstractRowResolver {
> // ....
> public static List<IAsyncResult> scheduleRepairs(ColumnFamily resolved,
> String table, DecoratedKey<?> key, List<ColumnFamily> versions,
> List<InetAddress> endpoints)
> {
> List<IAsyncResult> results = new
> ArrayList<IAsyncResult>(versions.size());
> for (int i = 0; i < versions.size(); i++)
> {
> // On some iteration we have to compare null and resolved which
> are obviously
> // not equals, so it will fire a ReadRequest, however it is not
> needed here
> ColumnFamily diffCf = ColumnFamily.diff(versions.get(i),
> resolved);
> if (diffCf == null)
> continue;
> // ....
> {code}
> Imagine the following situation:
> NodeA has X.1 // row X with the version 1
> NodeB has X.2
> NodeC has X.? // Unknown version, but because write was with Quorum it is 1
> or 2
> During the Quorum read from nodes A and B, Cassandra creates version 12 and
> send ReadRepair, so now nodes has the following content:
> NodeA has X.12
> NodeB has X.12
> which is correct, however Cassandra also will fire ReadRepair to NodeC. There
> is no need to do that, the next consistent read have a chance to be served by
> nodes {A, B} (no ReadRepair) or by pair {?, C} and in that case ReadRepair
> will be fired and brings nodeC to the consistent state
> Right now we are reading from the Index a lot and starting from some point in
> time we are getting TimeOutException because cluster is overloaded by the
> ReadRepairRequests *even* if all nodes has the same data :(
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