Re: Bug in new buffer freelist code

Tom Lane wrote:

> Note that buffer 160 gets cleared twice in this sequence.  The second
> time, the CDB for 174 gets found, leading to failure when 174 is cleared.
> 
> I believe the correct fix is to do CLEAR_BUFFERTAG on the buffer (and
> maybe the CDB too?) when returning a buffer to the freelist in 
> StrategyInvalidateBuffer.  It might also be worthwhile to add another
> BM_FLAG bit that specifically indicates a buffer is on the freelist,
> and set/clear/test that at appropriate spots.

That was the place I intended to do it.

> 
> I am actually of the opinion that the assertion code at the bottom of
> StrategyInvalidateBuffer is all wrong: it should *never* be possible
> to call StrategyInvalidateBuffer on something that's already in the
> freelist, and the only reason you had that in there was because of
> this mistaken failure to clear the buffertag, leading to wrong calls
> from linear searches of the buffer array.  I think you should just
> elog(ERROR) any time you fail to find a CDB in this routine.

That is corrent.


Jan

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