Bhaskar Muppana created CASSANDRA-12872:
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Summary: Paging reads and limit reads are missing some data
Key: CASSANDRA-12872
URL: https://issues.apache.org/jira/browse/CASSANDRA-12872
Project: Cassandra
Issue Type: Bug
Components: Coordination
Reporter: Bhaskar Muppana
Priority: Critical
Attachments: limiterr-reproduce.sh
We are seeing an issue with paging reads missing some small number of columns
when we do paging/limit reads. We get this on a single DC cluster itself when
both reads and writes are happening with QUORUM. Paging/limit reads see this
issue. I have attached the ccm based script which reproduces the problem.
* Keyspace RF - 3
* Table (id int, course text, marks int, primary key(id, course))
* replicas for partition key 1 - r1, r2 and r3
* insert (1, '1', 1) , (1, '2', 2), (1, '3', 3), (1, '4', 4), (1, '5', 5) -
succeeded on all 3 replicas
* insert (1, '6', 6) succeeded on r1 and r3, failed on r2
* delete (1, '2'), (1, '3'), (1, '4'), (1, '5') succeeded on r1 and r2, failed
on r3
* insert (1, '7', 7) succeeded on r1 and r2, failed on r3
Local data on 3 nodes looks like as below now
r1: (1, '1', 1), tombstone(2-5 records), (1, '6', 6), (1, '7', 7)
r2: (1, '1', 1), tombstone(2-5 records), (1, '7', 7)
r3: (1, '1', 1), (1, '2', 2), (1, '3', 3), (1, '4', 4), (1, '5', 5), (1,
'6', 6)
If we do a paging read with page_size 2, and if it gets data from r2 and r3,
then it will only get the data (1, '1', 1) and (1, '7', 7) skipping record 6.
This problem would happen if the same query is not doing paging but limit set
to 2 records.
Resolution code for reads works same for paging queries and normal queries.
Co-ordinator shouldn't respond back to client with records/columns that it
didn't have complete visibility on all required replicas (in this case 2
replicas). In above case, it is sending back record (1, '7', 7) back to client,
but its visibility on r3 is limited up to (1, '2', 2) and it is relying on just
r2 data to assume (1, '6', 6) doesn't exist, which is wrong. End of the
resolution all it can conclusively say any thing about is (1, '1', 1), which
exists and (1, '2', 2), which is deleted.
Ideally we should have different resolution implementation for paging/limit
queries.
We could reproduce this on 2.0.17, 2.1.16 and 3.0.9.
Seems like 3.0.9 we have ShortReadProtection transformation on list queries. I
assume that is to protect against the cases like above. But, we can reproduce
the issue in 3.0.9 as well.
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