Olivier Michallat created CASSANDRA-13992:
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Summary: Don't send new_metadata_id for conditional updates
Key: CASSANDRA-13992
URL: https://issues.apache.org/jira/browse/CASSANDRA-13992
Project: Cassandra
Issue Type: Bug
Reporter: Olivier Michallat
Priority: Minor
This is a follow-up to CASSANDRA-10786.
Given the table
{code}
CREATE TABLE foo (k int PRIMARY KEY)
{code}
And the prepared statement
{code}
INSERT INTO foo (k) VALUES (?) IF NOT EXISTS
{code}
The result set metadata changes depending on the outcome of the update:
* if the row didn't exist, there is only a single column \[applied] = true
* if it did, the result contains \[applied] = false, plus the current value of
column k.
The way this was handled so far is that the PREPARED response contains no
result set metadata, and therefore all EXECUTE messages have SKIP_METADATA =
false, and the responses always include the full (and correct) metadata.
CASSANDRA-10786 still sends the PREPARED response with no metadata, *but the
response to EXECUTE now contains a {{new_metadata_id}}*. The driver thinks it
is because of a schema change, and updates its local copy of the prepared
statement's result metadata.
The next EXECUTE is sent with SKIP_METADATA = true, but the server appears to
ignore that, and still sends the metadata in the response. So each response
includes the correct metadata, the driver uses it, and there is no visible
issue for client code.
The only drawback is that the driver updates its local copy of the metadata
unnecessarily, every time. We can work around that by only updating if we had
metadata before, at the cost of an extra volatile read. But I think the best
thing to do would be to never send a {{new_metadata_id}} in for a conditional
update.
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