Re: [HACKERS] GEQO Triggers Server Crash

Can we free only the plans we want to free in geqo? I don't mind having
a different free method in geqo vs. the rest of the optimizer.

---------------------------------------------------------------------------

Tom Lane wrote:
> Kris Jurka <jurka(at)ejurka(dot)com> writes:
> > [ GEQO doesn't work anymore in CVS tip ]
>
> Ugh. The proximate cause of this is the code I added recently to cache
> repeated calculations of the best inner indexscan for a given inner
> relation with potential outer relations. Since geqo_eval() releases
> all memory acquired during construction of a possible jointree, it
> releases the cached path info too. The next attempt to use the data
> fails.
>
> Naturally, ripping out the cache again doesn't strike me as an appealing
> solution.
>
> The narrowest fix would be to hack best_inner_indexscan() to switch into
> the context containing the parent RelOptInfo while it makes a cache
> entry. This seems kinda klugy but it would work.
>
> I wonder if we'd be better off not trying to reclaim memory in
> geqo_eval. Aside from presenting a constant risk of this sort of
> problem whenever someone hacks the optimizer, what it's really doing
> is discarding a whole lot of join cost estimates that are likely to
> be done over again in (some of) the following calls of geqo_eval.
> GEQO would certainly be a lot faster if we didn't release that info,
> and I'm not sure that the space cost would be as bad as the code
> comments claim. Any thoughts?
>
> This really just points up how messy memory management in the optimizer
> is at present. I wonder if anyone has ideas on improving it ...
>
> regards, tom lane
>
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