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pgsql: Export subxip[] for snapshots taken during recovery. 7+ messages / 1 participants [nested] [flat]
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_18_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/74c9832ca61037eec25b8f214fc71883494900d8 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/meson.build | 1 + src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 3 files changed, 147 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_15_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/ea3227bf2162db281d8d8560f14c49093b9b63f6 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 2 files changed, 146 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ master Details ------- https://git.postgresql.org/pg/commitdiff/79b101486c1d792600b79f90579b788385e85878 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/meson.build | 1 + src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 3 files changed, 147 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_16_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/d03ff3b7511c96abc4edc7b919200beb311059c0 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/meson.build | 1 + src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 3 files changed, 147 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_19_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/ef89c839cdc8398095be0d24e65a688115e38b72 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/meson.build | 1 + src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 3 files changed, 147 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_17_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/2ae67ada74d9e8407e4286414dfddf5d157f4dc3 Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/meson.build | 1 + src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 3 files changed, 147 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
* pgsql: Export subxip[] for snapshots taken during recovery. @ 2026-08-26 19:38 Peter Geoghegan <pg@bowt.ie> 0 siblings, 0 replies; 7+ messages in thread From: Peter Geoghegan @ 2026-08-26 19:38 UTC (permalink / raw) To: pgsql-committers@lists.postgresql.org Export subxip[] for snapshots taken during recovery. A snapshot taken during recovery stores all of its in-progress XIDs in subxip, every running top-level XID included, leaving xip empty. Unlike with other snapshots, its suboverflowed flag does not mean that subxip is redundant. We nevertheless treated it that way during snapshot export, so an importing session could see in-progress transactions as aborted. This misbehavior could also lead to hint bits being incorrectly set on the standby; affected tuples then wrongly appeared visible or invisible to sessions that never imported the snapshot. To fix, teach snapshot export to include the subxip[] array regardless of the overflow flag when the snapshot is taken during recovery. This is in line with how CopySnapshot() and SerializeSnapshot() already handle the same issue. Claude Code diagnosed this problem. The committed TAP test is a simplified version of the one that it wrote to demonstrate this bug. Oversight in commit 6c2003f8a, which enabled snapshot export and import during recovery. Author: Peter Geoghegan <pg@bowt.ie> Author: Bertrand Drouvot <bertranddrouvot.pg@gmail.com> Bug: #17846 Discussion: https://postgr.es/m/CAH2-WzmHVeYY%3Dpjz9x8DhhxVjXHX0pvoQ-MdiB1Tt6%3Do2GTiKg%40mail.gmail.com Discussion: https://postgr.es/m/17846-1a0e5ce976f4c01a@postgresql.org Backpatch-through: 14 Branch ------ REL_14_STABLE Details ------- https://git.postgresql.org/pg/commitdiff/9a1fa1f36e48394bb205eaf66cc33c18a6fe1bff Modified Files -------------- src/backend/utils/time/snapmgr.c | 58 ++++++++---- src/test/recovery/t/056_standby_snapshot_export.pl | 104 +++++++++++++++++++++ 2 files changed, 146 insertions(+), 16 deletions(-) ^ permalink raw reply [nested|flat] 7+ messages in thread
end of thread, other threads:[~2026-08-26 19:38 UTC | newest] Thread overview: 7+ messages (download: mbox mbox.gz follow: Atom feed) -- links below jump to the message on this page -- 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie> 2026-08-26 19:38 pgsql: Export subxip[] for snapshots taken during recovery. Peter Geoghegan <pg@bowt.ie>
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