Horton

Re: pg_trgm comparison bug on cross-architecture replication due to different char implementation

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Joe Conway <mail@joeconway.com>, Peter Eisentraut <peter@eisentraut.org>, Alexander Korotkov <aekorotkov@gmail.com>, "Guo, Adam" <adamguo@amazon.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>, Nathan Bossart <nathandbossart@gmail.com>, Jim Mlodgenski <jimmy76@gmail.com>
Date: 2024-09-19T01:46:44Z
Lists: pgsql-hackers 
On Tue, Sep 17, 2024 at 09:43:41PM -0700, Masahiko Sawada wrote:
> On Mon, Sep 16, 2024 at 9:24 AM Noah Misch <noah@leadboat.com> wrote:
> > On Thu, Sep 12, 2024 at 03:42:48PM -0700, Masahiko Sawada wrote:
> > > On Tue, Sep 10, 2024 at 3:05 PM Noah Misch <noah@leadboat.com> wrote:
> > > > On Tue, Sep 10, 2024 at 05:56:47PM -0400, Tom Lane wrote:
> > > > > Got it.  So now I'm wondering if we need all the complexity of storing
> > > > > stuff in the GIN metapages.  Could we simply read the (primary's)
> > > > > signedness out of pg_control and use that?
> >
> > > I've attached a PoC patch for this idea. We write  the default char
> > > signedness to the control file at initdb time. Then when comparing two
> > > trgms, pg_trgm opclasses use a comparison function based on the char
> > > signedness of the cluster. I've confirmed that the patch fixes the
> > > reported case at least.
> >
> > I agree that proves the concept.
> 
> Thanks. I like the simplicity of this approach. If we agree with this
> approach, I'd like to proceed with it.

Works for me.

> Regardless of what approach we take, I wanted to provide some
> regression tests for these changes, but I could not come up with a
> reasonable idea. It would be great if we could do something like
> 027_stream_regress.pl on cross-architecture replication. But just
> executing 027_stream_regress.pl on cross-architecture replication
> could not be sufficient since we would like to confirm query results
> as well. If we could have a reasonable tool or way, it would also help
> find other similar bugs related architectural differences.

Perhaps add a regress.c function that changes the control file flag and
flushes the change to disk?

Commits

  1. pg_upgrade: Check for the expected error message in TAP tests.

  2. Fix a typo in 005_char_signedness.pl test.

  3. Add test 005_char_signedness.pl to meson.build.

  4. Fix an issue with index scan using pg_trgm due to char signedness on different architectures.

  5. pg_upgrade: Add --set-char-signedness to set the default char signedness of new cluster.

  6. pg_upgrade: Preserve default char signedness value from old cluster.

  7. pg_resetwal: Add --char-signedness option to change the default char signedness.

  8. Add default_char_signedness field to ControlFileData.

  9. Remove unneeded nbtree array preprocessing assert.