| From: | John Naylor <john(dot)naylor(at)enterprisedb(dot)com> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> |
| Cc: | Nathan Bossart <nathandbossart(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de>, Matthias van de Meent <boekewurm+postgres(at)gmail(dot)com>, Yura Sokolov <y(dot)sokolov(at)postgrespro(dot)ru>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [PoC] Improve dead tuple storage for lazy vacuum |
| Date: | 2023-01-11 09:56:25 |
| Message-ID: | CAFBsxsHWX3vPGtuom5=p=Ve4NM3H9Pa5eYL3-ys+DUH4ZoxDmA@mail.gmail.com |
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| Lists: | pgsql-hackers |
I wrote:
> I see. IIUC from a brief re-reading of the code, saving that chunk would
only save us from re-loading "parent->shift" from L1 cache and shifting the
key. The cycles spent doing that seem small compared to the rest of the
work involved in growing a node. Expressions like "if (idx < 0) return
false;" return to an asserts-only variable, so in production builds, I
would hope that branch gets elided (I haven't checked).
On further reflection, this is completely false and I'm not sure what I was
thinking. However, for the update-inner case maybe we can assert that we
found a valid slot.
--
John Naylor
EDB: http://www.enterprisedb.com
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