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From "Sylvain Lebresne (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-8273) Allow filtering queries can return stale data
Date Thu, 06 Nov 2014 21:24:34 GMT
Sylvain Lebresne created CASSANDRA-8273:
-------------------------------------------

             Summary: Allow filtering queries can return stale data
                 Key: CASSANDRA-8273
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-8273
             Project: Cassandra
          Issue Type: Bug
            Reporter: Sylvain Lebresne


Data filtering is done replica side. That means that a single replica with stale data may
make the whole query return that stale data.

For instance, consider 3 replicas A, B and C, and the following situation:
{noformat}
CREATE TABLE test (k int PRIMARY KEY, v1 text, v2 int);
CREATE INDEX ON test(v1);
INSERT INTO test(k, v1, v2) VALUES (0, 'foo', 1);
{noformat}
with every replica up to date. Now, suppose that the following queries are done at {{QUORUM}}:
{noformat}
UPDATE test SET v2 = 2 WHERE k = 0;
SELECT * FROM test WHERE v1 = 'foo' AND v2 = 1;
{noformat}
then, if A and B acknowledge the insert but C respond to the read before having applied the
insert, then the now stale result will be returned. Let's note that this is a problem related
to filtering, not 2ndary indexes.

This issue share similarity with CASSANDRA-8272 but contrarily to that former issue, I'm not
sure how to fix it. Obviously, moving the filtering to the coordinator would remove that problem,
but doing so would, on top of not being trivial to implmenent, have serious performance impact
since we can't know in advance how much data will be filtered and we may have to redo query
to replica multiple times.




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