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https://issues.apache.org/jira/browse/CASSANDRA-10786?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15312088#comment-15312088
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Alex Petrov commented on CASSANDRA-10786:
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I've started implementing the changes on the driver side, and re-read your
suggestion and there's a bit more room for improvement. It looks cleaner and
should be closer to what you described. Also, requires less changes both client
and server side. You can find it
[here|https://github.com/ifesdjeen/cassandra/commit/98d46116fba1f1568416ca525c930f0e79595713]
(diff against prev revision of changes). In short, I reuse {{Rows}} and add a
flag to indicate that we "force" the metadata. At least in Java driver that
makes the implementation significantly simpler, as we can check flag, check
presence of two fields and update metadata or look it up otherwise, all in one
block without having to change too much.
I might be possible to omit {{statementId}} from the rows response. I've
included it for now, but we can change it any time, it's a small and isolated
change, hopefully.
> Include hash of result set metadata in prepared statement id
> ------------------------------------------------------------
>
> Key: CASSANDRA-10786
> URL: https://issues.apache.org/jira/browse/CASSANDRA-10786
> Project: Cassandra
> Issue Type: Bug
> Components: CQL
> Reporter: Olivier Michallat
> Assignee: Alex Petrov
> Priority: Minor
> Labels: client-impacting, doc-impacting, protocolv5
> Fix For: 3.x
>
>
> This is a follow-up to CASSANDRA-7910, which was about invalidating a
> prepared statement when the table is altered, to force clients to update
> their local copy of the metadata.
> There's still an issue if multiple clients are connected to the same host.
> The first client to execute the query after the cache was invalidated will
> receive an UNPREPARED response, re-prepare, and update its local metadata.
> But other clients might miss it entirely (the MD5 hasn't changed), and they
> will keep using their old metadata. For example:
> # {{SELECT * ...}} statement is prepared in Cassandra with md5 abc123,
> clientA and clientB both have a cache of the metadata (columns b and c)
> locally
> # column a gets added to the table, C* invalidates its cache entry
> # clientA sends an EXECUTE request for md5 abc123, gets UNPREPARED response,
> re-prepares on the fly and updates its local metadata to (a, b, c)
> # prepared statement is now in C*’s cache again, with the same md5 abc123
> # clientB sends an EXECUTE request for id abc123. Because the cache has been
> populated again, the query succeeds. But clientB still has not updated its
> metadata, it’s still (b,c)
> One solution that was suggested is to include a hash of the result set
> metadata in the md5. This way the md5 would change at step 3, and any client
> using the old md5 would get an UNPREPARED, regardless of whether another
> client already reprepared.
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