On Thu, May 15, 2014 at 9:18 AM, Andres Freund <and...@2ndquadrant.com> wrote: > On 2014-05-15 09:11:15 +0900, Michael Paquier wrote: >> When working on a decoder plugin, I have been pointed that it is >> incorrect to write changes in an output plugin while not being in the >> memory context where changes are written. > > That was a misunderstanding. It's perfectly alright to do so. The 'bug' > you have is that you sometimes wrote empty messages. Which > pg_recvlogical doesn't accept. There's little reason to allow doing so, > but for consistency we could probably ok to allow it. Yeah, thanks. Pushed a fix. Also I imagine that this is not really a problem, but is there an impact on the plugin if OutputPluginPrepareWrite is called and OutputPluginWrite is not for a single change? By looking at the code I am guessing that we use WalSndPrepareWrite for a plugin to prepare a message, and then WalSndWriteData to finish the work, so we end up with an empty message that is not sent to the backend. It doesn't matter much for test_decoding as it always writes a change, but shouldn't we discourage users to do so in the documentation? Something like a big-fat warning mentioning that using OutputPluginPrepareWrite called without OutputPluginWrite may result in stall messages stuck in the queue? -- Michael
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