| From: | Andres Freund <andres(at)anarazel(dot)de> |
|---|---|
| To: | David Rowley <dgrowleyml(at)gmail(dot)com> |
| Cc: | Tomas Vondra <tomas(dot)vondra(at)enterprisedb(dot)com>, Ronan Dunklau <ronan(dot)dunklau(at)aiven(dot)io>, Julien Rouhaud <rjuju123(at)gmail(dot)com>, PostgreSQL Developers <pgsql-hackers(at)lists(dot)postgresql(dot)org>, Tomas Vondra <tv(at)fuzzy(dot)cz> |
| Subject: | Re: Use generation context to speed up tuplesorts |
| Date: | 2022-02-23 02:25:04 |
| Message-ID: | 20220223022504.3ghth7eckjnnubxa@alap3.anarazel.de |
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| Lists: | pgsql-hackers |
Hi,
On 2022-02-18 12:10:51 +1300, David Rowley wrote:
> The other way I thought to fix it was by changing the logic for when
> generation blocks are freed. In the problem case mentioned above, the
> block being freed is the current block (which was just allocated). I
> made some changes to adjust this behaviour so that we no longer free
> the block when the final chunk is pfree()'d. Instead, that now lingers
> and can be reused by future allocations, providing they fit inside it.
That makes sense to me, as long as we keep just one such block.
> The problem I see with this method is that there still could be some
> pathological case that causes us to end up storing just a single tuple per
> generation block.
Crazy idea: Detect the situation, and recompact. Create a new context, copy
all the tuples over, delete the old context. That could be a win even in less
adversarial situations than "a single tuple per generation block".
Greetings,
Andres Freund
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