Horton

Re: pg_amcheck contrib application

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Mark Dilger <mark.dilger@enterprisedb.com>, Noah Misch <noah@leadboat.com>, Peter Geoghegan <pg@bowt.ie>, Thomas Munro <thomas.munro@gmail.com>, "Andrey M. Borodin" <x4mmm@yandex-team.ru>, Stephen Frost <sfrost@snowman.net>, Michael Paquier <michael@paquier.xyz>, Amul Sul <sulamul@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2021-03-16T18:45:13Z
Lists: pgsql-hackers 
Robert Haas <robertmhaas@gmail.com> writes:
> On Tue, Mar 16, 2021 at 1:48 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> No.  What should be happening there is that some arrays in the column
>> get larger alignment than they actually need, but that shouldn't cause
>> a problem (and has not done so, AFAIK, in the decades that it's been
>> like this).  As you say, deforming the tuple is going to rely on the
>> table's tupdesc for alignment; it can't know what is in the data.

> OK, I don't understand this. attalign is 'd', which is already the
> maximum possible, and even if it weren't, individual rows can't decide
> to use a larger OR smaller alignment than expected without breaking
> stuff.

> In what context is it OK to just add extra alignment padding?

It's *not* extra, according to pg_statistic's tuple descriptor.
Both forming and deforming of pg_statistic tuples should honor
that and locate stavaluesX values on d-aligned boundaries.

It could be that a particular entry is of an array type that
only requires i-alignment.  But that doesn't break anything,
it just means we inserted more padding than an omniscient
implementation would do.

(I suppose in some parallel universe there could be a machine
where i-alignment is stricter than d-alignment, and then we'd
have trouble.)

			regards, tom lane

Commits

  1. amcheck: Improve some confusing reports about TOAST problems.

  2. amcheck: Reword some messages and fix an alignment problem.

  3. amcheck: fix multiple problems with TOAST pointer validation

  4. amcheck: Remove duplicate XID/MXID bounds checks.

  5. amcheck: Fix verify_heapam's tuple visibility checking rules.

  6. nbtree VACUUM: Cope with buggy opclasses.

  7. Improve pg_amcheck's TAP test 003_check.pl.

  8. Fix a confusing amcheck corruption message.

  9. Doc: add note about how to run the pg_amcheck regression tests.

  10. In pg_amcheck tests, don't depend on perl's Q/q pack code.

  11. pg_amcheck: Keep trying to fix the tests.

  12. pg_amcheck: Try to fix still more test failures.

  13. Try to avoid apparent platform-dependency in IPC::Run

  14. Fix portability issues in pg_amcheck's 004_verify_heapam.pl.

  15. Try to fix compiler warnings.

  16. Add pg_amcheck, a CLI for contrib/amcheck.

  17. Refactor and generalize the ParallelSlot machinery.

  18. Remove old-style VACUUM FULL (which was known for a little while as