[CASSANDRA-3862] RowCache misses Updates

• Type: Bug
• Status: Resolved
• Priority: Normal
• Resolution: Fixed
• Fix Version/s: 1.1.0
• Severity: Normal
• Assignee: Sylvain Lebresne
• Reporter: Daniel Doubleday

Authors

Sylvain Lebresne

Reviewers

Jonathan Ellis

• Created: 06/Feb/12 17:17
• Updated: 16/Apr/19 09:32
• Resolved: 28/Feb/12 18:03

Description

While performing stress tests to find any race problems for CASSANDRA-2864 I guess I (re-)found one for the standard on-heap row cache.

During my stress test I hava lots of threads running with some of them only reading other writing and re-reading the value.

This seems to happen:

• Reader tries to read row A for the first time doing a getTopLevelColumns
• Row A which is not in the cache yet is updated by Writer. The row is not eagerly read during write (because we want fast writes) so the writer cannot perform a cache update
• Reader puts the row in the cache which is now missing the update

I already asked this some time ago on the mailing list but unfortunately didn't dig after I got no answer since I assumed that I just missed something. In a way I still do but haven't found any locking mechanism that makes sure that this should not happen.

The problem can be reproduced with every run of my stress test. When I restart the server the expected column is there. It's just missing from the cache.

To test I have created a patch that merges memtables with the row cache. With the patch the problem is gone.

I can also reproduce in 0.8. Haven't checked 1.1 but I haven't found any relevant change their either so I assume the same aplies there.