cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Stu Hood (JIRA)" <>
Subject [jira] [Created] (CASSANDRA-2503) Eagerly re-write data at read time ("superseding")
Date Tue, 19 Apr 2011 02:17:05 GMT
Eagerly re-write data at read time ("superseding")

                 Key: CASSANDRA-2503
             Project: Cassandra
          Issue Type: New Feature
          Components: Core
            Reporter: Stu Hood

Once CASSANDRA-2498 is implemented, it will be possible to implement an optimization to eagerly
rewrite ("supersede") data at read time. If a successful read needed to hit more than a certain
threshold of sstables, we can eagerly rewrite it in a new sstable, and 2498 will allow only
that file to be accessed. This basic approach would improve read performance considerably,
but would cause a lot of duplicate data to be written, and would make compaction's work more

Augmenting the basic idea, if when we superseded data in a file we marked it as superseded
somehow, the next compaction that touched that file could remove the data. Since our file
format is immutable, the values that a particular sstable superseded could be recorded in
a component of that sstable. If we always supersede at the "block" level (as defined by CASSANDRA-674
or CASSANDRA-47), then the list of superseded blocks could be represented using a generation
number and a bitmap of block numbers. Since 2498 would already allow for sstables to be eliminated
due to timestamps, this information would probably only be used at compaction time (by loading
all superseding information in the system for the sstables that are being compacted).

Initially described on [1608|!default.jspa?id=12477095&commentId=12920353].

This message is automatically generated by JIRA.
For more information on JIRA, see:

View raw message