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From "Benedict (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Tue, 28 Jul 2015 16:29:05 GMT


Benedict commented on CASSANDRA-7066:

If you lose one of these files you are SOL, there's not a lot that can be done to help a filesystem
failure over one of these. If you want to try and recover, the best we can do is point you
to the description of how they work and let you have a go at fixing it however you feel best.
Preferably restoring from backup.

If operators are messing with their sstable directory contents, this change simply means any
file present at startup will be considered a live file. That's all the operator should really
need to know, from that POV.

If restoring from backup, these logs should definitely all be deleted. I'm not sure what tools
we offer to hand hold backup/restore, but they should perhaps be made to understand this.

> 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or conversely not cleanup files that have been superceded); and 2) it's only used for a regular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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