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Re: Amcheck verification of GiST and GIN

Mark Dilger <mark.dilger@enterprisedb.com>

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From: Mark Dilger <mark.dilger@enterprisedb.com>
To: Tomas Vondra <tomas@vondra.me>, Kirill Reshke <reshkekirill@gmail.com>
Cc: "Andrey M. Borodin" <x4mmm@yandex-team.ru>, Alexander Lakhin <exclusion@gmail.com>, Andrey Borodin <amborodin86@gmail.com>, Peter Geoghegan <pg@bowt.ie>, Jose Arthur Benetasso Villanova <jose.arthur@gmail.com>, Andres Freund <andres@anarazel.de>, Nikolay Samokhvalov <samokhvalov@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2025-02-21T20:50:21Z
Lists: pgsql-hackers 

> On Feb 21, 2025, at 12:16 PM, Mark Dilger <mark.dilger@enterprisedb.com> wrote:
> 
> The pgbench script is not corrupting anything overtly, so this looks to either be a bug in gin or a bug in the check. 

I suspected the AccessShareLock taken by verify_gin() might be too weak, and upgraded that to ShareRowExclusiveLock so as to prevent the concurrent table modifications (and incidentally other concurrent verify_gin() calls), but to my surprise that didn't fix anything.  Even AccessExclusiveLock doesn't fix it.  So this seems to either be a bug in the checking code complaining about perfectly valid tuple order, or a bug in Gin corrupting its own entry tree page.

On successive runs, (instrumented to print out a bit more info), there doesn't seem to be any obvious pattern in where the corruption occurs.  The offset in the page changes, neither always being at the beginning, nor always at the maxoff; likewise the block where corruption is detected changes from run to run.  I've noticed that the rightlink for the page is always the page's block number plus one, but that might just be that I haven't run enough iterations yet to see counter-examples.

Could one of the patch authors take a look?  I don't have the time to chase this to conclusion just now.  Thanks.

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. amcheck: Fix posting tree checks in gin_index_check()

  2. amcheck: Fix parent key check in gin_index_check()

  3. amcheck: Fix checks of entry order for GIN indexes

  4. amcheck: Remove unused GinScanItem->parentlsn field

  5. amcheck: Test gin_index_check on a multicolumn index

  6. Remove incidental md5() function use from test

  7. amcheck: Add a GIN index to the CREATE INDEX CONCURRENTLY tests

  8. amcheck: Add a test with GIN index on JSONB data

  9. amcheck: Fix indentation in verify_gin.c

  10. amcheck: Add gin_index_check() to verify GIN index

  11. amcheck: Move common routines into a separate module

  12. Fix grammar in GIN README

  13. Avoid amcheck inline compression false positives.