Secondary indexes without read-before-write
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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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