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https://issues.apache.org/jira/browse/CASSANDRA-13992?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16251096#comment-16251096
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Alex Petrov edited comment on CASSANDRA-13992 at 11/14/17 8:39 AM:
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bq. METADATA_CHANGED tells the client if it needs to update its local copy of
the metadata.
You're right, great point. Sure, I've changed the patch to _always_ send
metadata (by avoiding setting {{SKIP_METADATA}} for LWTs) and _never_ send
metadata id when statement is LWT (by avoiding setting {{METADATA_CHANGED}} for
LWTs)). Technically, {{EMPTY}} part isn't even necessary in that case, but we
don't have to calculate it, so why not.
bq. I'm with Olivier that that's a hacky addition to the driver
There's no addition to the driver (also, was no addition in the previous
version of the patch). The only difference is that we can spare the driver a
couple of cycles. Behaviour was right in both cases.
I've pulled in the last version of the driver, added comments and prettified it
a bit. If we all agree that this behaviour is correct, can anyone take a short
look at it?
was (Author: ifesdjeen):
bq. METADATA_CHANGED tells the client if it needs to update its local copy of
the metadata.
You're right, great point. Sure, I've changed the patch to _always_ send
metadata (by avoiding setting {{SKIP_METADATA}} for LWTs) and _never_ send
metadata id when statement is LWT (by avoiding setting {{METADATA_CHANGED}} for
LWTs)). Technically, {{EMPTY}} part isn't even necessary in that case, but we
don't have to calculate it, so why not.
> I'm with Olivier that that's a hacky addition to the driver
There's no addition to the driver (also, was no addition in the previous
version of the patch). The only difference is that we can spare the driver a
couple of cycles. Behaviour was right in both cases.
I've pulled in the last version of the driver, added comments and prettified it
a bit. If we all agree that this behaviour is correct, can anyone take a short
look at it?
> 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.
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