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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-2897) Secondary indexes without read-before-write
Date Wed, 13 Jul 2011 17:47:01 GMT
Secondary indexes without read-before-write
-------------------------------------------

                 Key: CASSANDRA-2897
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2897
             Project: Cassandra
          Issue Type: Improvement
          Components: Core
    Affects Versions: 0.7.0
            Reporter: Sylvain Lebresne
            Priority: Minor


Currently, secondary index updates require a read-before-write to maintain the index consistency.
Keeping the index consistent at all time is not necessary however. We could let the (secondary)
index get inconsistent on writes and repair those on reads. This would be easy because on
reads, we make sure to request the indexed columns anyway, so we can just skip the row that
are not needed and repair the index at the same time.

This does trade work on writes for work on reads. However, read-before-write is sufficiently
costly that it will likely be a win overall.

There is (at least) two small technical difficulties here though:
# If we repair on read, this will be racy with writes, so we'll probably have to synchronize
there.
# We probably shouldn't only rely on read to repair and we should also have a task to repair
the index for things that are rarely read. It's unclear how to make that low impact though.

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