Re: Block-level CRC checks

Tom Lane wrote:

> Basically, you can't make any critical changes to a shared buffer
> if you haven't got exclusive lock on it. But that's exactly what
> this patch is assuming it can do.

It seems to me that the only possible way to close this hole is to
acquire an exclusive lock before calling FlushBuffers, not shared.
This lock would be held until the flag has been examined and reset; the
actual WAL record and write would continue with a shared lock, as now.

I'm wary of this "solution" because it's likely to reduce concurrency
tremendously ... thoughts?

(The alternative seems to be to abandon this idea for hint bit logging;
we'll need something else.)

--
Alvaro Herrera http://www.CommandPrompt.com/
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