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https://issues.apache.org/jira/browse/CASSANDRA-20829?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18013723#comment-18013723
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Stefan Miklosovic commented on CASSANDRA-20829:
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[~blambov] OK, pushed the branch.
How I tried to do that is that we will run through all expired rows just once.
So I am iterating over SSTableReaders first, and then for each row I need to
iterate over all indices, then create Indexer for each such row and remove.
If I iterated over Indexes first, then each pass would effectively run through
expired SSTables multiple times. Reading it all in one pass is better.
> Secondary index implementations do not integrate with IndexGCTransaction when
> compaction contains fully expired SSTables
> ------------------------------------------------------------------------------------------------------------------------
>
> Key: CASSANDRA-20829
> URL: https://issues.apache.org/jira/browse/CASSANDRA-20829
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Feature/2i Index, Local/Compaction, Local/Compaction/TWCS
> Reporter: Stefan Miklosovic
> Assignee: Stefan Miklosovic
> Priority: Normal
> Fix For: 4.0.x, 4.1.x
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> There is a test (1) which ensures that when data are TTLed and compacted,
> IndexGCTransaction is aware of that and it will invoke Indexer.removeRow()
> method eventually.
> However, this is not working properly when we have fully expired SSTables,
> e.g. as the result of a table being on TWCS and having TTL on that.
> The reason is that in CompactionTask, we are filtering out fully expired ones
> (2). These then do not go to the compaction process and then they are not
> reacted on in listener() (3) which contains this logic (4). Eventually,
> onRowMerge in IndexGCTransaction will make the diff and in its commit
> indexer.removeRow(row); will notify 2i about its removal.
>
> This integration is missing and it is quite a big problem because if there
> are custom secondary index implementations the fact that SSTables were fully
> expired is not propagated to them which means that data are never removed
> from whatever backend they use.
> The solution is to go to the compaction with fully expired SSTables as well
> _but only if we detected that respective column family has some indexes_
>
> (1)
> [https://github.com/apache/cassandra/blob/cassandra-4.1/test/unit/org/apache/cassandra/index/CustomIndexTest.java#L583-L607]
> (2)
> [https://github.com/apache/cassandra/blob/cassandra-4.1/src/java/org/apache/cassandra/db/compaction/CompactionTask.java#L174]
> (3)
> [https://github.com/apache/cassandra/blob/cassandra-4.1/src/java/org/apache/cassandra/db/compaction/CompactionIterator.java#L130]
> (4)
> [https://github.com/apache/cassandra/blob/cassandra-4.1/src/java/org/apache/cassandra/db/compaction/CompactionIterator.java#L235-L252]
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