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help / color / mirror / Atom feedFrom: Alexander Korotkov <[email protected]>
To: Amit Kapila <[email protected]>
Cc: Vitaly Davydov <[email protected]>
Cc: pgsql-hackers <[email protected]>
Cc: Masahiko Sawada <[email protected]>
Cc: [email protected]
Subject: Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly
Date: Tue, 3 Jun 2025 16:21:19 +0300
Message-ID: <CAPpHfdvxqjE+RZdoOODQZAmQip6NpvSH40DuvVFWuf_00ek-yQ@mail.gmail.com> (raw)
In-Reply-To: <CAA4eK1+VbBxYY-rG4B7Jq6TsYvdjt3d2nbUrs7p9-1sP5mH+sw@mail.gmail.com>
References: <1d12d2-67235980-35-19a406a0@63439497>
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<CAPpHfdtgwhFFpb8v8x2Humdj3F_DjaeBWY_h20g-Owh5tMArCA@mail.gmail.com>
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<CAA4eK1+eebaviZ9TCU4DHAOZzRRbWe0HgdjjQ1VVu7P_pEsiYQ@mail.gmail.com>
<CAPpHfdsk9_mrZaR_twwe6ntFUYCwu9SM1t4n6SmWNTZDZGefoQ@mail.gmail.com>
<CAA4eK1KMaPA5jir_SFu+qr3qu55OOdFWVZpuUkqTSGZ9fyPpHA@mail.gmail.com>
<2c1d-68344100-b7-3411b8c0@256938178>
<CAA4eK1LmVoZ8jm5Jt3DERN9Z=y6L6xj5O0asw0smWw31Y8KfVw@mail.gmail.com>
<CAPpHfdtp61pSt72KxxOnnV_Oj4OTAiKYCSTek0Pm87hVDod4Bg@mail.gmail.com>
<CAA4eK1Lmd-stXWrNqX9iXugjY=ahhe7zRfyq+-vN512xvF4G2w@mail.gmail.com>
<CAPpHfdsTiYQPywr4yeqVhUtA+eFdqisqcAOiTb+kiYhi9EVEvw@mail.gmail.com>
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<CAA4eK1+VbBxYY-rG4B7Jq6TsYvdjt3d2nbUrs7p9-1sP5mH+sw@mail.gmail.com>
On Mon, Jun 2, 2025 at 2:53 PM Amit Kapila <[email protected]> wrote:
>
> On Thu, May 29, 2025 at 5:29 PM Alexander Korotkov <[email protected]> wrote:
> >
> > On Tue, May 27, 2025 at 2:26 PM Amit Kapila <[email protected]> wrote:
> > > Yeah, we should be able to change ABI during beta, but I can't comment
> > > on the idea of effective_restart_lsn without seeing the patch or a
> > > detailed explanation of this idea.
> >
> > Could you, please, check the patch [1]. It implements this idea
> > except it names new field restart_lsn_flushed instead of
> > effective_restart_lsn.
> >
>
> This appears to be a better direction than the other patch, at least
> for HEAD. I noticed a few points while looking at the patch.
>
> 1. restart_lsn_flushed: Can we name it as last_saved_restart_lsn based
> on existing variable last_saved_confirmed_flush?
Good point, renamed.
> 2. There are no comments as to why this is considered only for
> persistent slots when CheckPointReplicationSlots doesn't have any such
> check.
Relevant comments added.
> 3. Please see if it makes sense to copy it in the copy_replication_slot.
Thank you for pointing, but I don't think this is necessary.
copy_replication_slot() calls ReplicationSlotSave(), which updates
last_saved_restart_lsn.
Also, I've changed ReplicationSlotsComputeRequiredLSN() call to
CheckPointReplicationSlots() to update required LSN after
SaveSlotToPath() updated last_saved_restart_lsn. This helps to pass
checks in 001_stream_rep.pl without additional hacks.
> Apart from these, I am not sure if there are still any pending
> comments in the thread to be handled for this patch, so please see to
> avoid missing anything.
>
> > > Now, you see my point related to restart_lsn computation for logical
> > > slots, it is better to also do some analysis of the problem related to
> > > xmin I have highlighted in one of my previous emails [1]. I see your
> > > response to it, but I feel someone needs to give it a try by writing a
> > > test and see the behavior. I am saying because logical slots took
> > > precaution of flushing to disk before updating shared values of xmin
> > > for a reason, whereas similar precautions are not taken for physical
> > > slots, so there could be a problem with that computation as well.
> >
> > I see LogicalConfirmReceivedLocation() performs correctly while
> > updating effective_catalog_xmin only after syncing the slot to the
> > disk. I don't see how effective_xmin gets updates with the logical
> > replication progress though. Could you get me some clue on this,
> > please?
> >
>
> As per my understanding, for logical slots, effective_xmin is only set
> during the initial copy phase (or say if one has to export a
> snapshot), after that, its value won't change. Please read the
> comments in CreateInitDecodingContext() where we set its value. If you
> still have questions about it, we can discuss further.
OK, thank you for the clarification. I've read the comments in
CreateInitDecodingContext() as you suggested. All of above makes me
think *_xmin fields are handled properly.
------
Regards,
Alexander Korotkov
Supabase
Attachments:
[application/octet-stream] v2-0001-Keep-WAL-segments-by-slot-s-flushed-restart-LSN.patch (6.8K, ../CAPpHfdvxqjE+RZdoOODQZAmQip6NpvSH40DuvVFWuf_00ek-yQ@mail.gmail.com/2-v2-0001-Keep-WAL-segments-by-slot-s-flushed-restart-LSN.patch)
download | inline diff:
From 0fe25ecf89396c26842d5889a1c4625002d08a3e Mon Sep 17 00:00:00 2001
From: Vitaly Davydov <[email protected]>
Date: Mon, 3 Mar 2025 17:02:15 +0300
Subject: [PATCH v2 1/2] Keep WAL segments by slot's flushed restart LSN
The slot data is flushed to the disk at the beginning of checkpoint. If
an existing slot is advanced in the middle of checkpoint execution, its
advanced restart LSN is taken to calculate the oldest LSN for WAL
segments removal at the end of checkpoint. If the node is restarted just
after the checkpoint, the slots data will be read from the disk at
recovery with the oldest restart LSN which can refer to removed WAL
segments.
The patch introduces a new in-memory state for slots -
flushed_restart_lsn which is used to calculate the oldest LSN for WAL
segments removal. This state is updated every time with the current
restart_lsn at the moment, when the slot is saving to disk.
---
src/backend/replication/slot.c | 57 ++++++++++++++++++++++++++++++++++
src/include/replication/slot.h | 7 +++++
2 files changed, 64 insertions(+)
diff --git a/src/backend/replication/slot.c b/src/backend/replication/slot.c
index 600b87fa9cb..c64f020742f 100644
--- a/src/backend/replication/slot.c
+++ b/src/backend/replication/slot.c
@@ -424,6 +424,7 @@ ReplicationSlotCreate(const char *name, bool db_specific,
slot->candidate_restart_valid = InvalidXLogRecPtr;
slot->candidate_restart_lsn = InvalidXLogRecPtr;
slot->last_saved_confirmed_flush = InvalidXLogRecPtr;
+ slot->last_saved_restart_lsn = InvalidXLogRecPtr;
slot->inactive_since = 0;
/*
@@ -1165,20 +1166,41 @@ ReplicationSlotsComputeRequiredLSN(void)
{
ReplicationSlot *s = &ReplicationSlotCtl->replication_slots[i];
XLogRecPtr restart_lsn;
+ XLogRecPtr last_saved_restart_lsn;
bool invalidated;
+ ReplicationSlotPersistency persistency;
if (!s->in_use)
continue;
SpinLockAcquire(&s->mutex);
+ persistency = s->data.persistency;
restart_lsn = s->data.restart_lsn;
invalidated = s->data.invalidated != RS_INVAL_NONE;
+ last_saved_restart_lsn = s->last_saved_restart_lsn;
SpinLockRelease(&s->mutex);
/* invalidated slots need not apply */
if (invalidated)
continue;
+ /*
+ * For persistent slot use last_saved_restart_lsn to compute the
+ * oldest LSN for removal of WAL segments. The segments between
+ * last_saved_restart_lsn and restart_lsn might be needed by a
+ * persistent slot in the case of database crash. Non-persistent
+ * slots can't survive the database crash, so we don't care about
+ * last_saved_restart_lsn for them.
+ */
+ if (persistency == RS_PERSISTENT)
+ {
+ if (last_saved_restart_lsn != InvalidXLogRecPtr &&
+ restart_lsn > last_saved_restart_lsn)
+ {
+ restart_lsn = last_saved_restart_lsn;
+ }
+ }
+
if (restart_lsn != InvalidXLogRecPtr &&
(min_required == InvalidXLogRecPtr ||
restart_lsn < min_required))
@@ -1216,7 +1238,9 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
{
ReplicationSlot *s;
XLogRecPtr restart_lsn;
+ XLogRecPtr last_saved_restart_lsn;
bool invalidated;
+ ReplicationSlotPersistency persistency;
s = &ReplicationSlotCtl->replication_slots[i];
@@ -1230,14 +1254,33 @@ ReplicationSlotsComputeLogicalRestartLSN(void)
/* read once, it's ok if it increases while we're checking */
SpinLockAcquire(&s->mutex);
+ persistency = s->data.persistency;
restart_lsn = s->data.restart_lsn;
invalidated = s->data.invalidated != RS_INVAL_NONE;
+ last_saved_restart_lsn = s->last_saved_restart_lsn;
SpinLockRelease(&s->mutex);
/* invalidated slots need not apply */
if (invalidated)
continue;
+ /*
+ * For persistent slot use last_saved_restart_lsn to compute the
+ * oldest LSN for removal of WAL segments. The segments between
+ * last_saved_restart_lsn and restart_lsn might be needed by a
+ * persistent slot in the case of database crash. Non-persistent
+ * slots can't survive the database crash, so we don't care about
+ * last_saved_restart_lsn for them.
+ */
+ if (persistency == RS_PERSISTENT)
+ {
+ if (last_saved_restart_lsn != InvalidXLogRecPtr &&
+ restart_lsn > last_saved_restart_lsn)
+ {
+ restart_lsn = last_saved_restart_lsn;
+ }
+ }
+
if (restart_lsn == InvalidXLogRecPtr)
continue;
@@ -1455,6 +1498,7 @@ ReplicationSlotReserveWal(void)
Assert(slot != NULL);
Assert(slot->data.restart_lsn == InvalidXLogRecPtr);
+ Assert(slot->last_saved_restart_lsn == InvalidXLogRecPtr);
/*
* The replication slot mechanism is used to prevent removal of required
@@ -1766,6 +1810,8 @@ InvalidatePossiblyObsoleteSlot(uint32 possible_causes,
*/
SpinLockAcquire(&s->mutex);
+ Assert(s->data.restart_lsn >= s->last_saved_restart_lsn);
+
restart_lsn = s->data.restart_lsn;
/* we do nothing if the slot is already invalid */
@@ -1835,7 +1881,10 @@ InvalidatePossiblyObsoleteSlot(uint32 possible_causes,
* just rely on .invalidated.
*/
if (invalidation_cause == RS_INVAL_WAL_REMOVED)
+ {
s->data.restart_lsn = InvalidXLogRecPtr;
+ s->last_saved_restart_lsn = InvalidXLogRecPtr;
+ }
/* Let caller know */
*invalidated = true;
@@ -2079,6 +2128,12 @@ CheckPointReplicationSlots(bool is_shutdown)
SaveSlotToPath(s, path, LOG);
}
LWLockRelease(ReplicationSlotAllocationLock);
+
+ /*
+ * Recompute the required LSN as SaveSlotToPath() updated
+ * last_saved_restart_lsn for slots.
+ */
+ ReplicationSlotsComputeRequiredLSN();
}
/*
@@ -2354,6 +2409,7 @@ SaveSlotToPath(ReplicationSlot *slot, const char *dir, int elevel)
if (!slot->just_dirtied)
slot->dirty = false;
slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush;
+ slot->last_saved_restart_lsn = cp.slotdata.restart_lsn;
SpinLockRelease(&slot->mutex);
LWLockRelease(&slot->io_in_progress_lock);
@@ -2569,6 +2625,7 @@ RestoreSlotFromDisk(const char *name)
slot->effective_xmin = cp.slotdata.xmin;
slot->effective_catalog_xmin = cp.slotdata.catalog_xmin;
slot->last_saved_confirmed_flush = cp.slotdata.confirmed_flush;
+ slot->last_saved_restart_lsn = cp.slotdata.restart_lsn;
slot->candidate_catalog_xmin = InvalidTransactionId;
slot->candidate_xmin_lsn = InvalidXLogRecPtr;
diff --git a/src/include/replication/slot.h b/src/include/replication/slot.h
index eb0b93b1114..e6fa9a4b5ab 100644
--- a/src/include/replication/slot.h
+++ b/src/include/replication/slot.h
@@ -215,6 +215,13 @@ typedef struct ReplicationSlot
* recently stopped.
*/
TimestampTz inactive_since;
+
+ /* Latest restart_lsn that has been flushed to disk. For persistent slots
+ * the flushed LSN should be taken into account when calculating the oldest
+ * LSN for WAL segments removal.
+ */
+ XLogRecPtr last_saved_restart_lsn;
+
} ReplicationSlot;
#define SlotIsPhysical(slot) ((slot)->data.database == InvalidOid)
--
2.39.5 (Apple Git-154)
[application/octet-stream] v2-0002-Add-TAP-tests-to-check-replication-slot-advance-d.patch (13.7K, ../CAPpHfdvxqjE+RZdoOODQZAmQip6NpvSH40DuvVFWuf_00ek-yQ@mail.gmail.com/3-v2-0002-Add-TAP-tests-to-check-replication-slot-advance-d.patch)
download | inline diff:
From 5aa06332d2cccae44e25583638796742346dd462 Mon Sep 17 00:00:00 2001
From: Alexander Korotkov <[email protected]>
Date: Sat, 24 May 2025 13:26:28 +0300
Subject: [PATCH v2 2/2] Add TAP tests to check replication slot advance during
the checkpoint
The new tests verify that logical and physical replication slots are still
valid after an immediate restart on checkpoint completion when the slot was
advanced during the checkpoint.
This commit introduces two new injection points to make these tests possible:
* checkpoint-before-old-wal-removal - triggered in the checkpointer process
just before old WAL segments cleanup;
* logical-replication-slot-advance-segment - triggered in
LogicalConfirmReceivedLocation() when restart_lsn was changed enough to
point to the next WAL segment.
Discussion: https://postgr.es/m/flat/1d12d2-67235980-35-19a406a0%4063439497
Author: Vitaly Davydov <[email protected]>
Author: Tomas Vondra <[email protected]>
Reviewed-by: Alexander Korotkov <[email protected]>
Backpatch-through: 17
---
src/backend/access/transam/xlog.c | 4 +
src/backend/replication/logical/logical.c | 18 +++
src/test/recovery/meson.build | 2 +
.../recovery/t/046_checkpoint_logical_slot.pl | 139 ++++++++++++++++++
.../t/047_checkpoint_physical_slot.pl | 133 +++++++++++++++++
5 files changed, 296 insertions(+)
create mode 100644 src/test/recovery/t/046_checkpoint_logical_slot.pl
create mode 100644 src/test/recovery/t/047_checkpoint_physical_slot.pl
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 1914859b2ee..47ffc0a2307 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -7498,6 +7498,10 @@ CreateCheckPoint(int flags)
if (PriorRedoPtr != InvalidXLogRecPtr)
UpdateCheckPointDistanceEstimate(RedoRecPtr - PriorRedoPtr);
+#ifdef USE_INJECTION_POINTS
+ INJECTION_POINT("checkpoint-before-old-wal-removal", NULL);
+#endif
+
/*
* Delete old log files, those no longer needed for last checkpoint to
* prevent the disk holding the xlog from growing full.
diff --git a/src/backend/replication/logical/logical.c b/src/backend/replication/logical/logical.c
index 1d56d0c4ef3..f1eb798f3e9 100644
--- a/src/backend/replication/logical/logical.c
+++ b/src/backend/replication/logical/logical.c
@@ -29,6 +29,7 @@
#include "postgres.h"
#include "access/xact.h"
+#include "access/xlog_internal.h"
#include "access/xlogutils.h"
#include "fmgr.h"
#include "miscadmin.h"
@@ -41,6 +42,7 @@
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
+#include "utils/injection_point.h"
#include "utils/inval.h"
#include "utils/memutils.h"
@@ -1825,9 +1827,13 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
{
bool updated_xmin = false;
bool updated_restart = false;
+ XLogRecPtr restart_lsn pg_attribute_unused();
SpinLockAcquire(&MyReplicationSlot->mutex);
+ /* remember the old restart lsn */
+ restart_lsn = MyReplicationSlot->data.restart_lsn;
+
/*
* Prevent moving the confirmed_flush backwards, as this could lead to
* data duplication issues caused by replicating already replicated
@@ -1881,6 +1887,18 @@ LogicalConfirmReceivedLocation(XLogRecPtr lsn)
/* first write new xmin to disk, so we know what's up after a crash */
if (updated_xmin || updated_restart)
{
+#ifdef USE_INJECTION_POINTS
+ XLogSegNo seg1,
+ seg2;
+
+ XLByteToSeg(restart_lsn, seg1, wal_segment_size);
+ XLByteToSeg(MyReplicationSlot->data.restart_lsn, seg2, wal_segment_size);
+
+ /* trigger injection point, but only if segment changes */
+ if (seg1 != seg2)
+ INJECTION_POINT("logical-replication-slot-advance-segment", NULL);
+#endif
+
ReplicationSlotMarkDirty();
ReplicationSlotSave();
elog(DEBUG1, "updated xmin: %u restart: %u", updated_xmin, updated_restart);
diff --git a/src/test/recovery/meson.build b/src/test/recovery/meson.build
index cb983766c67..92429d28402 100644
--- a/src/test/recovery/meson.build
+++ b/src/test/recovery/meson.build
@@ -54,6 +54,8 @@ tests += {
't/043_no_contrecord_switch.pl',
't/044_invalidate_inactive_slots.pl',
't/045_archive_restartpoint.pl',
+ 't/046_checkpoint_logical_slot.pl',
+ 't/047_checkpoint_physical_slot.pl'
],
},
}
diff --git a/src/test/recovery/t/046_checkpoint_logical_slot.pl b/src/test/recovery/t/046_checkpoint_logical_slot.pl
new file mode 100644
index 00000000000..b4265c4a6a5
--- /dev/null
+++ b/src/test/recovery/t/046_checkpoint_logical_slot.pl
@@ -0,0 +1,139 @@
+# Copyright (c) 2025, PostgreSQL Global Development Group
+#
+# This test verifies the case when the logical slot is advanced during
+# checkpoint. The test checks that the logical slot's restart_lsn still refers
+# to an existed WAL segment after immediate restart.
+#
+use strict;
+use warnings FATAL => 'all';
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+
+use Test::More;
+
+if ($ENV{enable_injection_points} ne 'yes')
+{
+ plan skip_all => 'Injection points not supported by this build';
+}
+
+my ($node, $result);
+
+$node = PostgreSQL::Test::Cluster->new('mike');
+$node->init;
+$node->append_conf('postgresql.conf',
+ "shared_preload_libraries = 'injection_points'");
+$node->append_conf('postgresql.conf', "wal_level = 'logical'");
+$node->start;
+$node->safe_psql('postgres', q(CREATE EXTENSION injection_points));
+
+# Create a simple table to generate data into.
+$node->safe_psql('postgres',
+ q{create table t (id serial primary key, b text)});
+
+# Create the two slots we'll need.
+$node->safe_psql('postgres',
+ q{select pg_create_logical_replication_slot('slot_logical', 'test_decoding')}
+);
+$node->safe_psql('postgres',
+ q{select pg_create_physical_replication_slot('slot_physical', true)});
+
+# Advance both slots to the current position just to have everything "valid".
+$node->safe_psql('postgres',
+ q{select count(*) from pg_logical_slot_get_changes('slot_logical', null, null)}
+);
+$node->safe_psql('postgres',
+ q{select pg_replication_slot_advance('slot_physical', pg_current_wal_lsn())}
+);
+
+# Run checkpoint to flush current state to disk and set a baseline.
+$node->safe_psql('postgres', q{checkpoint});
+
+# Generate some transactions to get RUNNING_XACTS.
+my $xacts = $node->background_psql('postgres');
+$xacts->query_until(
+ qr/run_xacts/,
+ q(\echo run_xacts
+SELECT 1 \watch 0.1
+\q
+));
+
+# Insert 2M rows; that's about 260MB (~20 segments) worth of WAL.
+$node->safe_psql('postgres',
+ q{insert into t (b) select md5(i::text) from generate_series(1,1000000) s(i)}
+);
+
+# Run another checkpoint to set a new restore LSN.
+$node->safe_psql('postgres', q{checkpoint});
+
+# Another 2M rows; that's about 260MB (~20 segments) worth of WAL.
+$node->safe_psql('postgres',
+ q{insert into t (b) select md5(i::text) from generate_series(1,1000000) s(i)}
+);
+
+# Run another checkpoint, this time in the background, and make it wait
+# on the injection point) so that the checkpoint stops right before
+# removing old WAL segments.
+note('starting checkpoint\n');
+
+my $checkpoint = $node->background_psql('postgres');
+$checkpoint->query_safe(
+ q(select injection_points_attach('checkpoint-before-old-wal-removal','wait'))
+);
+$checkpoint->query_until(
+ qr/starting_checkpoint/,
+ q(\echo starting_checkpoint
+checkpoint;
+\q
+));
+
+# Wait until the checkpoint stops right before removing WAL segments.
+note('waiting for injection_point\n');
+$node->wait_for_event('checkpointer', 'checkpoint-before-old-wal-removal');
+note('injection_point is reached');
+
+# Try to advance the logical slot, but make it stop when it moves to the next
+# WAL segment (this has to happen in the background, too).
+my $logical = $node->background_psql('postgres');
+$logical->query_safe(
+ q{select injection_points_attach('logical-replication-slot-advance-segment','wait');}
+);
+$logical->query_until(
+ qr/get_changes/,
+ q(
+\echo get_changes
+select count(*) from pg_logical_slot_get_changes('slot_logical', null, null) \watch 1
+\q
+));
+
+# Wait until the slot's restart_lsn points to the next WAL segment.
+note('waiting for injection_point\n');
+$node->wait_for_event('client backend',
+ 'logical-replication-slot-advance-segment');
+note('injection_point is reached');
+
+# OK, we're in the right situation: time to advance the physical slot, which
+# recalculates the required LSN, and then unblock the checkpoint, which
+# removes the WAL still needed by the logical slot.
+$node->safe_psql('postgres',
+ q{select pg_replication_slot_advance('slot_physical', pg_current_wal_lsn())}
+);
+
+# Continue the checkpoint.
+$node->safe_psql('postgres',
+ q{select injection_points_wakeup('checkpoint-before-old-wal-removal')});
+
+# Abruptly stop the server (1 second should be enough for the checkpoint
+# to finish; it would be better).
+$node->stop('immediate');
+
+$node->start;
+
+eval {
+ $node->safe_psql('postgres',
+ q{select count(*) from pg_logical_slot_get_changes('slot_logical', null, null);}
+ );
+};
+is($@, '', "Logical slot still valid");
+
+done_testing();
diff --git a/src/test/recovery/t/047_checkpoint_physical_slot.pl b/src/test/recovery/t/047_checkpoint_physical_slot.pl
new file mode 100644
index 00000000000..454e56b9bd2
--- /dev/null
+++ b/src/test/recovery/t/047_checkpoint_physical_slot.pl
@@ -0,0 +1,133 @@
+# Copyright (c) 2025, PostgreSQL Global Development Group
+#
+# This test verifies the case when the physical slot is advanced during
+# checkpoint. The test checks that the physical slot's restart_lsn still refers
+# to an existed WAL segment after immediate restart.
+#
+use strict;
+use warnings FATAL => 'all';
+
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+
+use Test::More;
+
+if ($ENV{enable_injection_points} ne 'yes')
+{
+ plan skip_all => 'Injection points not supported by this build';
+}
+
+my ($node, $result);
+
+$node = PostgreSQL::Test::Cluster->new('mike');
+$node->init;
+$node->append_conf('postgresql.conf',
+ "shared_preload_libraries = 'injection_points'");
+$node->append_conf('postgresql.conf', "wal_level = 'replica'");
+$node->start;
+$node->safe_psql('postgres', q(CREATE EXTENSION injection_points));
+
+# Create a simple table to generate data into.
+$node->safe_psql('postgres',
+ q{create table t (id serial primary key, b text)});
+
+# Create a physical replication slot.
+$node->safe_psql('postgres',
+ q{select pg_create_physical_replication_slot('slot_physical', true)});
+
+# Advance slot to the current position, just to have everything "valid".
+$node->safe_psql('postgres',
+ q{select pg_replication_slot_advance('slot_physical', pg_current_wal_lsn())}
+);
+
+# Run checkpoint to flush current state to disk and set a baseline.
+$node->safe_psql('postgres', q{checkpoint});
+
+# Insert 2M rows; that's about 260MB (~20 segments) worth of WAL.
+$node->safe_psql('postgres',
+ q{insert into t (b) select md5(i::text) from generate_series(1,100000) s(i)}
+);
+
+# Advance slot to the current position, just to have everything "valid".
+$node->safe_psql('postgres',
+ q{select pg_replication_slot_advance('slot_physical', pg_current_wal_lsn())}
+);
+
+# Run another checkpoint to set a new restore LSN.
+$node->safe_psql('postgres', q{checkpoint});
+
+# Another 2M rows; that's about 260MB (~20 segments) worth of WAL.
+$node->safe_psql('postgres',
+ q{insert into t (b) select md5(i::text) from generate_series(1,1000000) s(i)}
+);
+
+my $restart_lsn_init = $node->safe_psql('postgres',
+ q{select restart_lsn from pg_replication_slots where slot_name = 'slot_physical'}
+);
+chomp($restart_lsn_init);
+note("restart lsn before checkpoint: $restart_lsn_init");
+
+# Run another checkpoint, this time in the background, and make it wait
+# on the injection point) so that the checkpoint stops right before
+# removing old WAL segments.
+note('starting checkpoint');
+
+my $checkpoint = $node->background_psql('postgres');
+$checkpoint->query_safe(
+ q{select injection_points_attach('checkpoint-before-old-wal-removal','wait')}
+);
+$checkpoint->query_until(
+ qr/starting_checkpoint/,
+ q(\echo starting_checkpoint
+checkpoint;
+\q
+));
+
+# Wait until the checkpoint stops right before removing WAL segments.
+note('waiting for injection_point');
+$node->wait_for_event('checkpointer', 'checkpoint-before-old-wal-removal');
+note('injection_point is reached');
+
+# OK, we're in the right situation: time to advance the physical slot, which
+# recalculates the required LSN and then unblock the checkpoint, which
+# removes the WAL still needed by the physical slot.
+$node->safe_psql('postgres',
+ q{select pg_replication_slot_advance('slot_physical', pg_current_wal_lsn())}
+);
+
+# Continue the checkpoint.
+$node->safe_psql('postgres',
+ q{select injection_points_wakeup('checkpoint-before-old-wal-removal')});
+
+my $restart_lsn_old = $node->safe_psql('postgres',
+ q{select restart_lsn from pg_replication_slots where slot_name = 'slot_physical'}
+);
+chomp($restart_lsn_old);
+note("restart lsn before stop: $restart_lsn_old");
+
+# Abruptly stop the server (1 second should be enough for the checkpoint
+# to finish; it would be better).
+$node->stop('immediate');
+
+$node->start;
+
+# Get the restart_lsn of the slot right after restarting.
+my $restart_lsn = $node->safe_psql('postgres',
+ q{select restart_lsn from pg_replication_slots where slot_name = 'slot_physical'}
+);
+chomp($restart_lsn);
+note("restart lsn: $restart_lsn");
+
+# Get the WAL segment name for the slot's restart_lsn.
+my $restart_lsn_segment = $node->safe_psql('postgres',
+ "SELECT pg_walfile_name('$restart_lsn'::pg_lsn)");
+chomp($restart_lsn_segment);
+
+# Check if the required wal segment exists.
+note("required by slot segment name: $restart_lsn_segment");
+my $datadir = $node->data_dir;
+ok( -f "$datadir/pg_wal/$restart_lsn_segment",
+ "WAL segment $restart_lsn_segment for physical slot's restart_lsn $restart_lsn exists"
+);
+
+done_testing();
--
2.39.5 (Apple Git-154)
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Subject: Re: Slot's restart_lsn may point to removed WAL segment after hard restart unexpectedly
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