Re: [HACKERS] NOTIFY interlock broken (was Yipes, I'm getting bit by duplicate tuples)

> The good news: after much pain, I was able to develop a semi-repeatable
> test for that duplicate-tuple problem.  (It's a script of about 6300 SQL
> commands for five concurrent backends, which takes about 10 minutes to
> run and produces a corrupted table about one run out of two...)  And
> this test indicates that the current CVS sources don't have the bug.
> So, rather than expending a lot of effort trying to figure out just
> what the bug is in 6.3.2, we are going to cross our fingers and put our
> production application on 6.4beta.

That's good news.

> The bad news: this same script exposes a different bug in the current
> sources (and perhaps older releases too).  *Very* rarely, like less
> than one run out of ten, the test driver gets wedged or fails with an
> "out of memory" error.  I just traced this to its cause, and the cause
> is that a SELECT reply coming from the backend is corrupt.  In fact,
> what I see in libpq's input buffer is that a "NOTIFY" message has been
> inserted into the middle of the tuple data :-(.  So the interlock that
> supposedly prevents Async_NotifyFrontEnd() from being invoked during
> another command does not work reliably.
>
> I will look into this, but I could use advice from anyone who
> understands how that stuff is supposed to work.

Tom, I can't think of anyone who understands it better than you.

However, if you find something in the backend and need help, let me
know.

I will be on vacation from Sunday until Wednesday.

--
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