[
https://issues.apache.org/jira/browse/CASSANDRA-13992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16244458#comment-16244458
]
Olivier Michallat commented on CASSANDRA-13992:
-----------------------------------------------
bq. If C* thinks the metadata changed it will set the METADATA_CHANGED flag and
the driver should need to update it's metadata. TBH this isn't super clear from
the spec but appears to be what the code achieves here.
That makes sense, and indeed explains why the server ignores SKIP_METADATA.
I've tested your patch against a driver snapshot. The bound statement
executions now always return the same (empty) digest, but the problem is that
the initial preparation still returns a non-empty digest. So the driver
executes with that initial digest and gets METADATA_CHANGED with the empty
digest every time.
The prepare should also return an empty digest, which I think should be done
around
[here|https://github.com/kgreav/cassandra/blob/fa259fd79ea3e0a0fac8583a54c9c76464a653be/src/java/org/apache/cassandra/cql3/QueryProcessor.java#L444].
cc [~ifesdjeen]
> 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
> Assignee: Kurt Greaves
> 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.
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
---------------------------------------------------------------------
To unsubscribe, e-mail: commits-unsubscr...@cassandra.apache.org
For additional commands, e-mail: commits-h...@cassandra.apache.org
