| From: | Andrew Gierth <andrew(at)tao11(dot)riddles(dot)org(dot)uk> |
|---|---|
| To: | Chapman Flack <chap(at)anastigmatix(dot)net> |
| Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: lazy detoasting |
| Date: | 2018-04-10 04:30:56 |
| Message-ID: | 87bmerhfbu.fsf@news-spur.riddles.org.uk |
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| Thread: | |
| Lists: | pgsql-hackers |
>>>>> "Chapman" == Chapman Flack <chap(at)anastigmatix(dot)net> writes:
Chapman> AFAICS, that is *all* that comment block has to say about why
Chapman> there's an active snapshot stack. I believe you are saying it
Chapman> has another important function, namely that its top element is
Chapman> what tells the executor what can be seen.
That's not precisely true - ultimately, the routines that do actual
scans take the snapshot to use as a parameter, and the executor mostly
references the snapshot from the EState; but a bunch of places do
require that ActiveSnapshot be set to the currently applicable snapshot
(e.g. for queries inside stable functions nested inside the main query).
--
Andrew (irc:RhodiumToad)
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