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https://issues.apache.org/jira/browse/CASSANDRA-15861?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17188529#comment-17188529
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Stefan Miklosovic commented on CASSANDRA-15861:
-----------------------------------------------

Thanks [~blerer], but anyway, a test as I mentioned would be awesome to see 
when the code / logic which is touching this has changed little bit and we 
would be sure it is just computed right. The fact that we found that issue as 
part of 15406 is telling ... It would also simplify a lot my patch because 
right now I am literally parsing the output of netstats and I track that these 
numbers do make sense and the total is eventually equal to that sum. I am not 
so strong in internals so I am not able to write that "low level" test on my 
own. But ultimately it is not about me having things easier, but imho we should 
really test that and this patch seems to be like a good candidate to do it.

> Mutating sstable component may race with entire-sstable-streaming(ZCS) 
> causing checksum validation failure
> ----------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-15861
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-15861
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Consistency/Repair, Consistency/Streaming, 
> Local/Compaction
>            Reporter: ZhaoYang
>            Assignee: ZhaoYang
>            Priority: Normal
>             Fix For: 4.0-beta
>
>
> Flaky dtest: [test_dead_sync_initiator - 
> repair_tests.repair_test.TestRepair|https://ci-cassandra.apache.org/view/all/job/Cassandra-devbranch-dtest/143/testReport/junit/dtest.repair_tests.repair_test/TestRepair/test_dead_sync_initiator/]
> {code:java|title=stacktrace}
> Unexpected error found in node logs (see stdout for full details). Errors: 
> [ERROR [Stream-Deserializer-127.0.0.1:7000-570871f3] 2020-06-03 04:05:19,081 
> CassandraEntireSSTableStreamReader.java:145 - [Stream 
> 6f1c3360-a54f-11ea-a808-2f23710fdc90] Error while reading sstable from stream 
> for table = keyspace1.standard1
> org.apache.cassandra.io.sstable.CorruptSSTableException: Corrupted: 
> /home/cassandra/cassandra/cassandra-dtest/tmp/dtest-te4ty0r9/test/node3/data0/keyspace1/standard1-5f5ab140a54f11eaa8082f23710fdc90/na-2-big-Statistics.db
>       at 
> org.apache.cassandra.io.sstable.metadata.MetadataSerializer.maybeValidateChecksum(MetadataSerializer.java:219)
>       at 
> org.apache.cassandra.io.sstable.metadata.MetadataSerializer.deserialize(MetadataSerializer.java:198)
>       at 
> org.apache.cassandra.io.sstable.metadata.MetadataSerializer.deserialize(MetadataSerializer.java:129)
>       at 
> org.apache.cassandra.io.sstable.metadata.MetadataSerializer.mutate(MetadataSerializer.java:226)
>       at 
> org.apache.cassandra.db.streaming.CassandraEntireSSTableStreamReader.read(CassandraEntireSSTableStreamReader.java:140)
>       at 
> org.apache.cassandra.db.streaming.CassandraIncomingFile.read(CassandraIncomingFile.java:78)
>       at 
> org.apache.cassandra.streaming.messages.IncomingStreamMessage$1.deserialize(IncomingStreamMessage.java:49)
>       at 
> org.apache.cassandra.streaming.messages.IncomingStreamMessage$1.deserialize(IncomingStreamMessage.java:36)
>       at 
> org.apache.cassandra.streaming.messages.StreamMessage.deserialize(StreamMessage.java:49)
>       at 
> org.apache.cassandra.streaming.async.StreamingInboundHandler$StreamDeserializingTask.run(StreamingInboundHandler.java:181)
>       at 
> io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
>       at java.lang.Thread.run(Thread.java:748)
> Caused by: java.io.IOException: Checksums do not match for 
> /home/cassandra/cassandra/cassandra-dtest/tmp/dtest-te4ty0r9/test/node3/data0/keyspace1/standard1-5f5ab140a54f11eaa8082f23710fdc90/na-2-big-Statistics.db
> {code}
>  
> In the above test, it executes "nodetool repair" on node1 and kills node2 
> during repair. At the end, node3 reports checksum validation failure on 
> sstable transferred from node1.
> {code:java|title=what happened}
> 1. When repair started on node1, it performs anti-compaction which modifies 
> sstable's repairAt to 0 and pending repair id to session-id.
> 2. Then node1 creates {{ComponentManifest}} which contains file lengths to be 
> transferred to node3.
> 3. Before node1 actually sends the files to node3, node2 is killed and node1 
> starts to broadcast repair-failure-message to all participants in 
> {{CoordinatorSession#fail}}
> 4. Node1 receives its own repair-failure-message and fails its local repair 
> sessions at {{LocalSessions#failSession}} which triggers async background 
> compaction.
> 5. Node1's background compaction will mutate sstable's repairAt to 0 and 
> pending repair id to null via  
> {{PendingRepairManager#getNextRepairFinishedTask}}, as there is no more 
> in-progress repair.
> 6. Node1 actually sends the sstable to node3 where the sstable's STATS 
> component size is different from the original size recorded in the manifest.
> 7. At the end, node3 reports checksum validation failure when it tries to 
> mutate sstable level and "isTransient" attribute in 
> {{CassandraEntireSSTableStreamReader#read}}.
> {code}
> Currently, entire-sstable-streaming requires sstable components to be 
> immutable, because \{{ComponentManifest}}
> with component sizes are sent before sending actual files. This isn't a 
> problem in legacy streaming as STATS file length didn't matter.
>  
> Ideally it will be great to make sstable STATS metadata immutable, just like 
> other sstable components, so we don't have to worry this special case.
> I can think of 2 ways:
>  # Make STATS mutation as a proper compaction to create hard link on the 
> compacting sstable components with a new descriptor, except STATS files which 
> will be copied entirely. Then mutation will be applied on the new STATS file. 
> At the end, old sstable will be released. This ensures all sstable components 
> are immutable and shouldn't make these special compaction tasks slower.
>  # Change STATS metadata format to use fixed length encoding for repair info



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