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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Tue, 11 Aug 2015 09:05:45 GMT


Benedict commented on CASSANDRA-7066:

bq. Is this what you intended?

Yes, this is just to ensure that when we consciously abort the transaction (due to internal
error, say) we make certain we cannot also commit somehow (although this should be protected
against). Like I say, this one's more to put my mind at ease and introduce further safety,
it's probably not necessary, but I appreciate you putting it in.

bq. When upgrading we will not recognize transactions for tables in an old format, which I
assume is also a good thing?

Probably not, really (unless you mean "old" as in those a user running an alpha version may
have created). We will want to perform cleanup of any in-progress transactions on startup
before upgrade. Having the sstable version in the txn log name is probably a good idea still,
to help us upgrade the transaction format itself if we want to. But we need to be able to
read any compatible prior version and tidy up.

> Simplify (and unify) cleanup of compaction leftovers
> ----------------------------------------------------
>                 Key: CASSANDRA-7066
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Benedict
>            Assignee: Stefania
>            Priority: Minor
>              Labels: benedict-to-commit, compaction
>             Fix For: 3.0 alpha 1
>         Attachments: 7066.txt
> Currently we manage a list of in-progress compactions in a system table, which we use
to cleanup incomplete compactions when we're done. The problem with this is that 1) it's a
bit clunky (and leaves us in positions where we can unnecessarily cleanup completed files,
or conversely not cleanup files that have been superceded); and 2) it's only used for a regular
compaction - no other compaction types are guarded in the same way, so can result in duplication
if we fail before deleting the replacements.
> I'd like to see each sstable store in its metadata its direct ancestors, and on startup
we simply delete any sstables that occur in the union of all ancestor sets. This way as soon
as we finish writing we're capable of cleaning up any leftovers, so we never get duplication.
It's also much easier to reason about.

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