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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Mon, 03 Aug 2015 08:10:05 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14651571#comment-14651571
] 

Benedict commented on CASSANDRA-7066:
-------------------------------------

bq. Will this cause problems if the alpha goes out before this ticket is committed?

We should be fine, since we're changing on-wire serialization between alpha and beta also,
so I guess we're OK with some upgrade problems between the two (we don't really want or expect
anyone to use alpha except for dev, I would guess). [~jbellis]?

bq. However all classes implementing MetadataComponent implement them so I left them with
a comment.  Also, without it it seems a scrub test was failing (unsure if related though).

I guess it's possible we compare metadata at the end of a scrub to confirm it's equivalent.
It's somewhat ugly that we will treat all compaction metadata as equal, but probably not worth
worrying about here.

Otherwise SGTM, I'll review it shortly.

> Simplify (and unify) cleanup of compaction leftovers
> ----------------------------------------------------
>
>                 Key: CASSANDRA-7066
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-7066
>             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or conversely not cleanup files that have been superceded); and 2) it's only used for a regular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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