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From "Stu Hood (JIRA)" <j...@apache.org>
Subject [jira] Issue Comment Edited: (CASSANDRA-1608) Redesigned Compaction
Date Tue, 12 Oct 2010 22:16:33 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-1608?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12920377#action_12920377
] 

Stu Hood edited comment on CASSANDRA-1608 at 10/12/10 6:16 PM:
---------------------------------------------------------------

> I guess Cassandra would only need a fixed count of exactly 2, making it a non-issue.
Yea, I think we realized this at the same time... rather than deleting from the original filter,
you could mark it as superseded in a separate filter for the sstable, which could be sized
to accommodate the number of supersedes/deletes you would need to do before you'd want to
run a compaction for the sstable: less than 2 bits totally actually.

EDIT: Nevermind... false positives in the second set would cause the wrong data to be dropped.

      was (Author: stuhood):
    > I guess Cassandra would only need a fixed count of exactly 2, making it a non-issue.
Yea, I think we realized this at the same time... rather than deleting from the original filter,
you could mark it as superseded in a separate filter for the sstable, which could be sized
to accommodate the number of supersedes/deletes you would need to do before you'd want to
run a compaction for the sstable: less than 2 bits totally actually.
  
> Redesigned Compaction
> ---------------------
>
>                 Key: CASSANDRA-1608
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-1608
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Chris Goffinet
>             Fix For: 0.7.1
>
>
> After seeing the I/O issues in CASSANDRA-1470, I've been doing some more thinking on
this subject that I wanted to lay out.
> I propose we redo the concept of how compaction works in Cassandra. At the moment, compaction
is kicked off based on a write access pattern, not read access pattern. In most cases, you
want the opposite. You want to be able to track how well each SSTable is performing in the
system. If we were to keep statistics in-memory of each SSTable, prioritize them based on
most accessed, and bloom filter hit/miss ratios, we could intelligently group sstables that
are being read most often and schedule them for compaction. We could also schedule lower priority
maintenance on SSTable's not often accessed.
> I also propose we limit the size of each SSTable to a fix sized, that gives us the ability
to  better utilize our bloom filters in a predictable manner. At the moment after a certain
size, the bloom filters become less reliable. This would also allow us to group data most
accessed. Currently the size of an SSTable can grow to a point where large portions of the
data might not actually be accessed as often.

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