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Re: Adding REPACK [concurrently]

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andres Freund <andres@anarazel.de>, Noah Misch <noah@leadboat.com>, vignesh C <vignesh21@gmail.com>, Antonin Houska <ah@cybertec.at>, Srinath Reddy Sadipiralla <srinath2133@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Mihail Nikalayeu <mihailnikalayeu@gmail.com>, Matthias van de Meent <boekewurm+postgres@gmail.com>, Pg Hackers <pgsql-hackers@lists.postgresql.org>, Robert Treat <rob@xzilla.net>
Date: 2026-04-07T08:40:25Z
Lists: pgsql-hackers 
On 2026-Apr-07, Tom Lane wrote:

> Maybe you saw this already, but BF member skink is failing on
> src/test/modules/injection_points/specs/repack.spec:
> 
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=skink&dt=2026-04-06%2022%3A50%3A41

Thanks, I hadn't, and I cannot reproduce it locally.  Anyway, the
valgrind report is

==1617044== VALGRINDERROR-BEGIN
==1617044== Syscall param pwrite64(buf) points to uninitialised byte(s)
==1617044==    at 0x6704003: pwrite (pwrite64.c:25)
==1617044==    by 0x44AAC72: pg_pwritev (pg_iovec.h:101)
==1617044==    by 0x44AC6B5: FileWriteV (fd.c:2280)
==1617044==    by 0x44A8EC4: FileWrite (fd.h:245)
==1617044==    by 0x44A8EC4: BufFileDumpBuffer (buffile.c:538)
==1617044==    by 0x44A9034: BufFileFlush (buffile.c:724)
==1617044==    by 0x44A9661: BufFileClose (buffile.c:418)
==1617044==    by 0x426C4DE: export_initial_snapshot (repack_worker.c:346)
==1617044==    by 0x426CA17: RepackWorkerMain (repack_worker.c:145)
==1617044==    by 0x441D3AD: BackgroundWorkerMain (bgworker.c:865)
==1617044==    by 0x44219D9: postmaster_child_launch (launch_backend.c:265)
==1617044==  Address 0x12d745e2 is 106 bytes inside a block of size 8,272 client-defined
==1617044==    at 0x4661CFE: palloc (mcxt.c:1411)
==1617044==    by 0x44A8C54: makeBufFileCommon (buffile.c:121)
==1617044==    by 0x44A933F: BufFileCreateFileSet (buffile.c:272)
==1617044==    by 0x426C4A5: export_initial_snapshot (repack_worker.c:341)
==1617044==    by 0x426CA17: RepackWorkerMain (repack_worker.c:145)
==1617044==    by 0x441D3AD: BackgroundWorkerMain (bgworker.c:865)
==1617044==    by 0x44219D9: postmaster_child_launch (launch_backend.c:265)
==1617044==    by 0x4423B6D: StartBackgroundWorker (postmaster.c:4197)
==1617044==    by 0x4423DB8: maybe_start_bgworkers (postmaster.c:4362)
==1617044==    by 0x4425119: LaunchMissingBackgroundProcesses (postmaster.c:3437)
==1617044==    by 0x4426A75: ServerLoop (postmaster.c:1737)
==1617044==    by 0x44280DC: PostmasterMain (postmaster.c:1412)
==1617044==  Uninitialised value was created by a stack allocation
==1617044==    at 0x4674D39: SerializeSnapshot (snapmgr.c:1737)
==1617044== 
==1617044== VALGRINDERROR-END

and obviously BufFileCreateFileSet() is being called by existing code
already and it doesn't fail, so I *think* the problem might be that
SerializedSnapshotData has some padding bytes that are being written.
Maybe using palloc0() is enough?  I'll try that.

If that doesn't silence skink, I guess my next step is to reproduce
skink's environment more precisely ...

-- 
Álvaro Herrera               48°01'N 7°57'E  —  https://www.EnterpriseDB.com/
"Uno puede defenderse de los ataques; contra los elogios se esta indefenso"

Commits

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

  1. Allow old WAL recycling during REPACK CONCURRENTLY

  2. Advance restart_lsn more eagerly in LogicalConfirmReceivedLocation

  3. Remove unnecessary signal handler change

  4. Improve REPACK (CONCURRENTLY) error messages some more

  5. Revert "Allow logical replication snapshots to be database-specific"

  6. Move REPACK (CONCURRENTLY) test out of stock regression tests

  7. REPACK: do not require REPLICATION or LOGIN

  8. Add missing initialization

  9. Simplify declaration of memcpy target

  10. Reserve replication slots specifically for REPACK

  11. doc: Add an example of REPACK (CONCURRENTLY)

  12. Allow logical replication snapshots to be database-specific

  13. Avoid different-size pointer-to-integer cast

  14. Fix valgrind failure

  15. Add CONCURRENTLY option to REPACK

  16. Rename cluster.c to repack.c (and corresponding .h)

  17. Allow index_create to suppress index_build progress reporting

  18. Make index_concurrently_create_copy more general

  19. Document the 'command' column of pg_stat_progress_repack

  20. Introduce the REPACK command

  21. Toggle logical decoding dynamically based on logical slot presence.

  22. Split vacuumdb to create vacuuming.c/h

  23. Remove ReorderBufferTupleBuf structure.

  24. Revert changes to CONCURRENTLY that "sped up" Xmin advance

  25. VACUUM: ignore indexing operations with CONCURRENTLY