pgwire: empty query should result in emptyresponse, not error/commandcomplete

[knz]

Found by @fishcakez in #5582 (comment):

An empty query will fail with an error, postgresql handles this with an EmptyQueryResponse message, instead of CommandComplete. This may not matter to cockroach.

Note that this is may appear to be a dup of #3852 but the fix to that issue didn't change what happens for empty queries.

[knz]

cc @mjibson @dt

[dt]

Huh, I thought I fixed this a long time ago, and we even have a test for it: TestCmdCompleteVsEmptyStatements

[dt]

@knz can you clarify "the fix to that issue [#3852] didn't change what happens for empty queries."... I thought that that was exactly what that changed.

[knz]

@fishcakez could you give more details about how you isolated this specific issue in your use case?

[fishcakez]

The reference issue seems to refer to using the simple Query messages to send multiple queries (of which some are empty). The situation we encountered (running the test suite for a postgres client against cockroach) is doing a single empty (prepared) query using Parse, Describe, Execute. I did not check for which message of the 3 the error occurs. However postgres will return the EmptyQueryResponse and so the test for our client fails.

[tlvenn]

@mjibson any chance to pull that fix soon ?

[maddyblue]

I'm waiting on lib/pq#500 to get merged (which I don't control), otherwise we can't write a test for this. Sorry for the delay. @tamird do you have write access to lib/pq? Would you be willing to review + merge that PR?

[tamird]

Sadly I do not have commit over there.

On Tue, Sep 20, 2016 at 2:03 PM, Matt Jibson notifications@github.com
wrote:

I'm waiting on lib/pq#500 lib/pq#500 to get
merged (which I don't control), otherwise we can't write a test for this.
Sorry for the delay. @tamird https://github.com/tamird do you have
write access to lib/pq? Would you be willing to review + merge that PR?

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[tlvenn]

Hope this can finally be fixed now the changes have been merged in lib/pq. Thanks for your work @mjibson and @tamird !