[jira] [Commented] (CASSANDRA-9060) Anticompaction hangs on bloom filter bitset serialization

["Benedict (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CASSANDRA-9060?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14530295#comment-14530295 ] 

Benedict commented on CASSANDRA-9060:
-------------------------------------

[~grddev] apologies for dropping the ball on this. it's a busy time as we ramp up to 3.0, and my workflow ignores tickets I'm reviewing that aren't marked 'Patch Available'. I'll see if we can get this integrated in the near future; it's a shame we missed 2.1.5.

> Anticompaction hangs on bloom filter bitset serialization 
> ----------------------------------------------------------
>
>                 Key: CASSANDRA-9060
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9060
>             Project: Cassandra
>          Issue Type: Bug
>            Reporter: Gustav Munkby
>            Assignee: Gustav Munkby
>            Priority: Minor
>             Fix For: 2.1.x
>
>         Attachments: 0001-another-tweak-to-9060.patch, 2.1-9060-simple.patch, trunk-9060.patch
>
>
> I tried running an incremental repair against a 15-node vnode-cluster with roughly 500GB data running on 2.1.3-SNAPSHOT, without performing the suggested migration steps. I manually chose a small range for the repair (using --start/end-token). The actual repair part took almost no time at all, but the anticompactions took a lot of time (not surprisingly).
> Obviously, this might not be the ideal way to run incremental repairs, but I wanted to look into what made the whole process so slow. The results were rather surprising. The majority of the time was spent serializing bloom filters.
> The reason seemed to be two-fold. First, the bloom-filters generated were huge (probably because the original SSTables were large). With a proper migration to incremental repairs, I'm guessing this would not happen. Secondly, however, the bloom filters were being written to the output one byte at a time (with quite a few type-conversions on the way) to transform the little-endian in-memory representation to the big-endian on-disk representation.
> I have implemented a solution where big-endian is used in-memory as well as on-disk, which obviously makes de-/serialization much, much faster. This introduces some slight overhead when checking the bloom filter, but I can't see how that would be problematic. An obvious alternative would be to still perform the serialization/deserialization using a byte array, but perform the byte-order swap there.



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