Horton

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

Peter Eisentraut <peter@eisentraut.org>

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From: Peter Eisentraut <peter@eisentraut.org>
To: Tom Lane <tgl@sss.pgh.pa.us>, Alexander Korotkov <aekorotkov@gmail.com>
Cc: "Guo, Adam" <adamguo@amazon.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2024-05-03T12:20:21Z
Lists: pgsql-hackers 
On 30.04.24 19:29, Tom Lane wrote:
>> 1) Assume that char signedness is somehow a property of bits-on-disk
>> even though it's weird.  Then pg_trgm indexes are correct, but we need
>> to store char signedness in pg_control.
>> 2) Assume that char signedness is not a property of bits-on-disk.
>> Then pg_trgm indexes are buggy and need to be fixed.
>> What do you think?
> Also, the bigger picture here is the seeming assumption that "if
> we change pg_trgm then it will be safe to replicate from x86 to
> arm".  I don't believe that that's a good idea and I'm unwilling
> to promise that it will work, regardless of what we do about
> char signedness.  That being the case, I don't want to invest a
> lot of effort in the signedness issue.  Option (1) is clearly
> a small change with little if any risk of future breakage.

But note that option 1 would prevent some replication that is currently 
working.

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.