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Olivier Michallat edited comment on CASSANDRA-13992 at 11/13/17 5:18 PM: ------------------------------------------------------------------------- [~ifesdjeen] that would work, the driver can treat an empty {{new_metadata_id}} as "don't update my local copy". Namely, changing [this line|https://github.com/datastax/java-driver/blob/6eeb8b2193ab5b50b73b0d9a533e775265f11007/driver-core/src/main/java/com/datastax/driver/core/ArrayBackedResultSet.java#L83] to: {code} if (newMetadataId != null && newMetadataId.bytes.length > 0) { {code} However that feels kind of hacky. Consider how we would have to explain that in the protocol spec: {quote} - <new_metadata_id> is \[short bytes] representing the new, changed resultset metadata. The new metadata ID must also be used in subsequent executions of the corresponding prepared statement, if any, *except if it is empty*. {quote} It would make so much more sense to force {{METADATA_CHANGED}} to *false* for conditional updates, isn't there any way we can do that? was (Author: omichallat): [~ifesdjeen] that would work, the driver can treat an empty {{new_metadata_id}} as "don't update my local copy". Namely, changing [this line|https://github.com/datastax/java-driver/blob/6eeb8b2193ab5b50b73b0d9a533e775265f11007/driver-core/src/main/java/com/datastax/driver/core/ArrayBackedResultSet.java#L83] to: {code} if (newMetadataId != null && newMetadataId.bytes.length > 0) { {code} However that feels kind of hacky. Consider how we would have to update the protocol spec to explain this: {quote} - <new_metadata_id> is \[short bytes] representing the new, changed resultset metadata. The new metadata ID must also be used in subsequent executions of the corresponding prepared statement, if any, *except if it is empty*. {quote} It would make so much more sense to force {{METADATA_CHANGED}} to *false* for conditional statements, isn't there any way we can do that? > 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