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From "Yuki Morishita (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-7066) Simplify (and unify) cleanup of compaction leftovers
Date Tue, 22 Apr 2014 18:32:15 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-7066?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13977170#comment-13977170
] 

Yuki Morishita commented on CASSANDRA-7066:
-------------------------------------------

Ancestors are used to prevent over counting counters by loading unnecessary SSTables (leftover
from compaction).
CASSANDRA-5151 is created to improve this.

As Jonathan mentioned, we store them in SSTable metadata, but it causes heap pressure when
using LCS (CASSANDRA-5342).
CASSANDRA-5342 makes it to read as necessary and not to keep in heap forever.
In fact, even in 2.1 ancestors are recorded in [one of SSTable metadata|https://github.com/apache/cassandra/blob/cassandra-2.1/src/java/org/apache/cassandra/io/sstable/metadata/CompactionMetadata.java#L42]
and used to calculate the new ancestors during compaction.


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or conversely not cleanup files that have been superceded); and 2) it's only used for a regular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