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From "Benedict (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Tue, 22 Apr 2014 18:44:14 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13977174#comment-13977174
] 

Benedict edited comment on CASSANDRA-7066 at 4/22/14 6:42 PM:
--------------------------------------------------------------

So we already have it, the problem is we don't want to keep it resident? What's the problem
with just reading it on startup for cleaning up compaction left overs?

For cleaning up compaction all we need is direct ancestors, but it's not really a problem
to read all ancestors and filter based on those files we know exist to avoid unnecessary heap
pressure. Seems much more robust and simple to reason about to me...?

If we only have direct ancestors, we wouldn't be permitted to delete any sstable that shadows
another that isn't itself already deleted (which can be delayed for a period)... but this
still gives us better behaviour than the current setup. This could be achieved with an OpOrder
reasonably easily, or simply rescheduling the DeletingTask if any of its ancestors are still
alive.

Right now, we can "finish compaction" with the replacement sstable finished and ready to read,
but the replaced/expired sstables untidied. If something happens at this point, we end up
with all of the tables.


was (Author: benedict):
So we already have it, the problem is we don't want to keep it resident? What's the problem
with just reading it on startup for cleaning up compaction left overs?

For cleaning up compaction all we need is direct ancestors, but it's not really a problem
to read all ancestors and filter based on those files we know exist to avoid unnecessary heap
pressure. Seems much more robust and simple to reason about to me...?

> 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
>            Priority: Minor
>             Fix For: 3.0
>
>
> 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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