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From "Jeremy Hanna (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-3843) Unnecessary ReadRepair request during RangeScan
Date Tue, 21 Feb 2012 14:30:35 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-3843?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13212617#comment-13212617
] 

Jeremy Hanna commented on CASSANDRA-3843:
-----------------------------------------

I did repairs on all the nodes and then compacts on all the nodes. Then I did a pig job to
simply count the number of rows in the column family. Again I think the overall writes were
reduced but there are writes going on. I need to turn debug on and do the same test again.
I did the compactions at 6:42 and the range scans at 14:16:

-rw-r--r-- 1 root root 40106228511 Feb 21 06:42 account_snapshot-g-792-Data.db
-rw-r--r-- 1 root root   206884816 Feb 21 06:42 account_snapshot-g-792-Filter.db
-rw-r--r-- 1 root root  2913796038 Feb 21 06:42 account_snapshot-g-792-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 06:42 account_snapshot-g-792-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-793-Compacted
-rw-r--r-- 1 root root      287286 Feb 21 14:16 account_snapshot-g-793-Data.db
-rw-r--r-- 1 root root         976 Feb 21 14:16 account_snapshot-g-793-Filter.db
-rw-r--r-- 1 root root       20857 Feb 21 14:16 account_snapshot-g-793-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:16 account_snapshot-g-793-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-794-Compacted
-rw-r--r-- 1 root root    87770771 Feb 21 14:17 account_snapshot-g-794-Data.db
-rw-r--r-- 1 root root      293944 Feb 21 14:17 account_snapshot-g-794-Filter.db
-rw-r--r-- 1 root root     6377968 Feb 21 14:17 account_snapshot-g-794-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:17 account_snapshot-g-794-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-795-Compacted
-rw-r--r-- 1 root root    78459166 Feb 21 14:17 account_snapshot-g-795-Data.db
-rw-r--r-- 1 root root      262600 Feb 21 14:17 account_snapshot-g-795-Filter.db
-rw-r--r-- 1 root root     5698156 Feb 21 14:17 account_snapshot-g-795-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:17 account_snapshot-g-795-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-796-Compacted
-rw-r--r-- 1 root root    69838937 Feb 21 14:17 account_snapshot-g-796-Data.db
-rw-r--r-- 1 root root      234000 Feb 21 14:17 account_snapshot-g-796-Filter.db
-rw-r--r-- 1 root root     5077447 Feb 21 14:17 account_snapshot-g-796-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:17 account_snapshot-g-796-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-797-Compacted
-rw-r--r-- 1 root root    68094433 Feb 21 14:17 account_snapshot-g-797-Data.db
-rw-r--r-- 1 root root      227808 Feb 21 14:17 account_snapshot-g-797-Filter.db
-rw-r--r-- 1 root root     4943098 Feb 21 14:17 account_snapshot-g-797-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:17 account_snapshot-g-797-Statistics.db
-rw-r--r-- 1 root root   304163307 Feb 21 14:20 account_snapshot-g-798-Data.db
-rw-r--r-- 1 root root     1019776 Feb 21 14:20 account_snapshot-g-798-Filter.db
-rw-r--r-- 1 root root    22096669 Feb 21 14:20 account_snapshot-g-798-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:20 account_snapshot-g-798-Statistics.db
-rw-r--r-- 1 root root    65874829 Feb 21 14:18 account_snapshot-g-799-Data.db
-rw-r--r-- 1 root root      220192 Feb 21 14:18 account_snapshot-g-799-Filter.db
-rw-r--r-- 1 root root     4777809 Feb 21 14:18 account_snapshot-g-799-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:18 account_snapshot-g-799-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-800-Compacted
-rw-r--r-- 1 root root    50067413 Feb 21 14:18 account_snapshot-g-800-Data.db
-rw-r--r-- 1 root root      167416 Feb 21 14:18 account_snapshot-g-800-Filter.db
-rw-r--r-- 1 root root     3632313 Feb 21 14:18 account_snapshot-g-800-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:18 account_snapshot-g-800-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-801-Compacted
-rw-r--r-- 1 root root    50575719 Feb 21 14:18 account_snapshot-g-801-Data.db
-rw-r--r-- 1 root root      169160 Feb 21 14:18 account_snapshot-g-801-Filter.db
-rw-r--r-- 1 root root     3669880 Feb 21 14:18 account_snapshot-g-801-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:18 account_snapshot-g-801-Statistics.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-g-802-Compacted
-rw-r--r-- 1 root root    41788766 Feb 21 14:19 account_snapshot-g-802-Data.db
-rw-r--r-- 1 root root      139776 Feb 21 14:19 account_snapshot-g-802-Filter.db
-rw-r--r-- 1 root root     3033069 Feb 21 14:19 account_snapshot-g-802-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:19 account_snapshot-g-802-Statistics.db
-rw-r--r-- 1 root root    46547146 Feb 21 14:19 account_snapshot-g-803-Data.db
-rw-r--r-- 1 root root      155720 Feb 21 14:19 account_snapshot-g-803-Filter.db
-rw-r--r-- 1 root root     3378457 Feb 21 14:19 account_snapshot-g-803-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:19 account_snapshot-g-803-Statistics.db
-rw-r--r-- 1 root root   142719184 Feb 21 14:20 account_snapshot-g-804-Data.db
-rw-r--r-- 1 root root      478576 Feb 21 14:19 account_snapshot-g-804-Filter.db
-rw-r--r-- 1 root root    10356119 Feb 21 14:20 account_snapshot-g-804-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:20 account_snapshot-g-804-Statistics.db
-rw-r--r-- 1 root root    55373874 Feb 21 14:19 account_snapshot-g-805-Data.db
-rw-r--r-- 1 root root      185160 Feb 21 14:19 account_snapshot-g-805-Filter.db
-rw-r--r-- 1 root root     4017391 Feb 21 14:19 account_snapshot-g-805-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:19 account_snapshot-g-805-Statistics.db
-rw-r--r-- 1 root root    46399227 Feb 21 14:19 account_snapshot-g-806-Data.db
-rw-r--r-- 1 root root      155120 Feb 21 14:19 account_snapshot-g-806-Filter.db
-rw-r--r-- 1 root root     3365947 Feb 21 14:19 account_snapshot-g-806-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:19 account_snapshot-g-806-Statistics.db
-rw-r--r-- 1 root root    58491393 Feb 21 14:19 account_snapshot-g-807-Data.db
-rw-r--r-- 1 root root      196048 Feb 21 14:19 account_snapshot-g-807-Filter.db
-rw-r--r-- 1 root root     4253922 Feb 21 14:19 account_snapshot-g-807-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:19 account_snapshot-g-807-Statistics.db
-rw-r--r-- 1 root root    47609635 Feb 21 14:20 account_snapshot-g-808-Data.db
-rw-r--r-- 1 root root      159320 Feb 21 14:20 account_snapshot-g-808-Filter.db
-rw-r--r-- 1 root root     3456985 Feb 21 14:20 account_snapshot-g-808-Index.db
-rw-r--r-- 1 root root        4276 Feb 21 14:20 account_snapshot-g-808-Statistics.db
-rw-r--r-- 1 root root    46923060 Feb 21 14:20 account_snapshot-tmp-g-809-Data.db
-rw-r--r-- 1 root root           0 Feb 21 14:20 account_snapshot-tmp-g-809-Index.db
-rw-r--r-- 1 root root    49693602 Feb 21 14:20 account_snapshot-tmp-g-810-Data.db
-rw-r--r-- 1 root root      166600 Feb 21 14:20 account_snapshot-tmp-g-810-Filter.db
-rw-r--r-- 1 root root     3614750 Feb 21 14:20 account_snapshot-tmp-g-810-Index.db
                
> 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-v2.txt, 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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