Sylvain Lebresne created CASSANDRA-8273:
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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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