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From "Jonathan Ellis (JIRA)" <>
Subject [jira] [Commented] (CASSANDRA-1608) Redesigned Compaction
Date Fri, 26 Aug 2011 19:55:29 GMT


Jonathan Ellis commented on CASSANDRA-1608:

... didn't quite get the DT registration right the first time, but it's committed again now.

Still getting seeing a few failures when I make Leveled the default for the test suite.  Most
are bogus (e.g. test assuming it can request compaction of arbitrary sstables) but some are

[junit] Test org.apache.cassandra.db.ColumnFamilyStoreTest FAILED (crashed)
[junit] Testsuite: org.apache.cassandra.db.ColumnFamilyTest

[junit] Test org.apache.cassandra.db.ColumnFamilyStoreTest FAILED (crashed)
[junit] Testsuite: org.apache.cassandra.db.ColumnFamilyTest

Actually, it's quite likely that these are manifestations of the CASSANDRA-3085 problem, which
is more likely to bite us in practice now that there are many more sstables generated.  So
I'll address that first before worrying about these.

Additional note: test suite runs about 20% slower for me w/ Leveled compactions.  Unsure if
that should be expected.

> Redesigned Compaction
> ---------------------
>                 Key: CASSANDRA-1608
>                 URL:
>             Project: Cassandra
>          Issue Type: Improvement
>          Components: Core
>            Reporter: Chris Goffinet
>            Assignee: Benjamin Coverston
>         Attachments: 1608-22082011.txt, 1608-v2.txt, 1608-v4.txt, 1608-v5.txt
> 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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