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From: Tom Lane <[email protected]>
To: Michael Paquier <[email protected]>
Cc: Postgres hackers <[email protected]>
Subject: Re: Re-add recently-removed tests for ltree and intarray
Date: Thu, 14 May 2026 22:09:29 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>

Michael Paquier <[email protected]> writes:
> Some of you may have noticed that some regression tests have been
> removed due to some noise in the buildfarm, as of commit 906ea101d0d5.

> We did not have time to do something for this release, unfortunately.
> It is possible to reproduce the incompatibility by setting
> max_stack_depth to a low value, where the first new query of ltree and
> intarray would fail, when written in their original shape.

Just to add a little more color to this --- what we discovered after
there was time for some investigation was that:

(a) the stack-overflow failure occurred in the findoprnd() function
of intarray/_int_bool.c or ltree/ltxtquery_io.c.

(b) the failure only appeared on buildfarm members running on ppc64
or s390x.  I determined by examining assembly code that ppc64 uses
about 3X as much stack per call level in this function as x86_64;
probably s390x is similar.  That was enough to overrun our default
max_stack_depth on these architectures, even though the same case
passed on the machines we'd tested on.

(c) even with minimum max_stack_depth, the test passed using gcc
but not clang.  Again examining assembly code, gcc is smart enough
to collapse the tail-recursion calls in findoprnd() into looping,
causing the original test case's right-deep query tree to consume
essentially zero stack space.  clang doesn't do that, at least not
on those arches at default optimization level.  You can make gcc
fail too with -O0.

So it'd be good to verify on a few oddball platforms that Michael's
new attempt is OK.  It should theoretically work, but ...

			regards, tom lane

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