Date: Wed, 13 Sep 2023 16:48:22 -0500
From: Seebs <seebs@seebs.net>
To: "Euler Taveira" <euler@eulerto.com>
Cc: pgsql-docs@lists.postgresql.org
Subject: Re: index access method documentation light on details on
 ii_AmCache
Message-ID: <20230913164822.41e4c0bd@seebsdell>
In-Reply-To: <a52489dd-e6ca-425b-a23d-d0139728419f@app.fastmail.com>
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On Wed, 13 Sep 2023 15:48:41 -0300
"Euler Taveira" <euler@eulerto.com> wrote:

> Unless you change it, ii_Context is CurrentMemoryContext (see
> makeIndexInfo). Hence, your AM state information is freed when the
> current memory context is freed.

A thing I am now wondering:

Is there anything in the postgresql documentation which explains this,
or says when a given memory context will be freed? Like, is the
ii_Context there for the lifetime of the index? For the lifetime of the
query? For the lifetime of a single insert operation?

I've found a reference to it in a third-party blog post, but I actually
can't find anything in the docs explaining memory contexts, and a bit
of experimenting makes me think they are doing things that aren't
obvious to me. For instance, I tried *not* deleting a memory context
when done with it, then looping doing a query which tried to create and
populate it, and... memory usage did not go up. Making me think that
maybe it gets reused? Or maybe it's implicitly deleted because it had
a parent context?

-s