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Commit42496cb

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amcheck: Distinguish interrupted page deletion from corruption.
This prevents false-positive reports about "the first child of leftmosttarget page is not leftmost of its level", "block %u is not leftmost"and "left link/right link pair". They appeared if amcheck ran beforeVACUUM cleaned things, after a cluster exited recovery between thefirst-stage and second-stage WAL records of a deletion. Back-patch tov11 (all supported versions).Reviewed by Peter Geoghegan.Discussion:https://postgr.es/m/20231005025232.c7.nmisch@google.com
1 parent162b38a commit42496cb

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2 files changed

+168
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2 files changed

+168
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lines changed

‎contrib/amcheck/t/005_pitr.pl

Lines changed: 89 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,89 @@
1+
# Copyright (c) 2021-2023, PostgreSQL Global Development Group
2+
3+
# Test integrity of intermediate states by PITR to those states
4+
use strict;
5+
use warnings;
6+
use PostgreSQL::Test::Cluster;
7+
use PostgreSQL::Test::Utils;
8+
use Test::More;
9+
10+
# origin node: generate WAL records of interest.
11+
my$origin = PostgreSQL::Test::Cluster->new('origin');
12+
$origin->init(has_archiving=> 1,allows_streaming=> 1);
13+
$origin->append_conf('postgresql.conf','autovacuum = off');
14+
$origin->start;
15+
$origin->backup('my_backup');
16+
# Create a table with each of 6 PK values spanning 1/4 of a block. Delete the
17+
# first four, so one index leaf is eligible for deletion. Make a replication
18+
# slot just so pg_waldump will always have access to later WAL.
19+
my$setup =<<EOSQL;
20+
BEGIN;
21+
CREATE EXTENSION amcheck;
22+
CREATE TABLE not_leftmost (c text);
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ALTER TABLE not_leftmost ALTER c SET STORAGE PLAIN;
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INSERT INTO not_leftmost
25+
SELECT repeat(n::text, database_block_size / 4)
26+
FROM generate_series(1,6) t(n), pg_control_init();
27+
ALTER TABLE not_leftmost ADD CONSTRAINT not_leftmost_pk PRIMARY KEY (c);
28+
DELETE FROM not_leftmost WHERE c ~ '^[1-4]';
29+
SELECT pg_create_physical_replication_slot('for_waldump', true, false);
30+
COMMIT;
31+
EOSQL
32+
$origin->safe_psql('postgres',$setup);
33+
my$before_vacuum_walfile =
34+
$origin->safe_psql('postgres',"SELECT pg_walfile_name(pg_current_wal_lsn())");
35+
# VACUUM to delete the aforementioned leaf page. Force an XLogFlush() by
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# dropping a permanent table. That way, the XLogReader infrastructure can
37+
# always see VACUUM's records, even under synchronous_commit=off. Finally,
38+
# find the LSN of that VACUUM's last UNLINK_PAGE record.
39+
my$vacuum =<<EOSQL;
40+
SET synchronous_commit = off;
41+
VACUUM (VERBOSE, INDEX_CLEANUP ON) not_leftmost;
42+
CREATE TABLE XLogFlush ();
43+
DROP TABLE XLogFlush;
44+
SELECT pg_walfile_name(pg_current_wal_flush_lsn());
45+
EOSQL
46+
my$after_unlink_walfile =$origin->safe_psql('postgres',$vacuum);
47+
$origin->stop;
48+
my$unlink_lsn =do {
49+
local%ENV =$origin->_get_env();
50+
my$stdout;
51+
run_log(['pg_waldump','-p',$origin->data_dir .'/pg_wal',
52+
$before_vacuum_walfile,$after_unlink_walfile],
53+
'>', \$stdout);
54+
$stdout =~m|^rmgr: Btree .*, lsn: ([/0-9A-F]+), .*, desc: UNLINK_PAGE left|m;
55+
$1;
56+
};
57+
die"did not find UNLINK_PAGE record"unless$unlink_lsn;
58+
59+
# replica node: amcheck at notable points in the WAL stream
60+
my$replica = PostgreSQL::Test::Cluster->new('replica');
61+
$replica->init_from_backup($origin,'my_backup',has_restoring=> 1);
62+
$replica->append_conf('postgresql.conf',
63+
"recovery_target_lsn = '$unlink_lsn'");
64+
$replica->append_conf('postgresql.conf','recovery_target_inclusive = off');
65+
$replica->append_conf('postgresql.conf','recovery_target_action = promote');
66+
$replica->start;
67+
$replica->poll_query_until('postgres',"SELECT pg_is_in_recovery() = 'f';")
68+
ordie"Timed out while waiting for PITR promotion";
69+
# recovery done; run amcheck
70+
my$debug ="SET client_min_messages = 'debug1'";
71+
my ($rc,$stderr);
72+
$rc =$replica->psql(
73+
'postgres',
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"$debug; SELECT bt_index_parent_check('not_leftmost_pk', true)",
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stderr=> \$stderr);
76+
printSTDERR$stderr,"\n";
77+
is($rc, 0,"bt_index_parent_check passes");
78+
like(
79+
$stderr,
80+
qr/interrupted page deletion detected/,
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"bt_index_parent_check: interrupted page deletion detected");
82+
$rc =$replica->psql(
83+
'postgres',
84+
"$debug; SELECT bt_index_check('not_leftmost_pk', true)",
85+
stderr=> \$stderr);
86+
printSTDERR$stderr,"\n";
87+
is($rc, 0,"bt_index_check passes");
88+
89+
done_testing();

‎contrib/amcheck/verify_nbtree.c

Lines changed: 79 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -146,6 +146,9 @@ static void bt_check_every_level(Relation rel, Relation heaprel,
146146
boolrootdescend);
147147
staticBtreeLevelbt_check_level_from_leftmost(BtreeCheckState*state,
148148
BtreeLevellevel);
149+
staticboolbt_leftmost_ignoring_half_dead(BtreeCheckState*state,
150+
BlockNumberstart,
151+
BTPageOpaquestart_opaque);
149152
staticvoidbt_recheck_sibling_links(BtreeCheckState*state,
150153
BlockNumberbtpo_prev_from_target,
151154
BlockNumberleftcurrent);
@@ -774,7 +777,7 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
774777
*/
775778
if (state->readonly)
776779
{
777-
if (!P_LEFTMOST(opaque))
780+
if (!bt_leftmost_ignoring_half_dead(state,current,opaque))
778781
ereport(ERROR,
779782
(errcode(ERRCODE_INDEX_CORRUPTED),
780783
errmsg("block %u is not leftmost in index \"%s\"",
@@ -828,8 +831,16 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
828831
*/
829832
}
830833

831-
/* Sibling links should be in mutual agreement */
832-
if (opaque->btpo_prev!=leftcurrent)
834+
/*
835+
* Sibling links should be in mutual agreement. There arises
836+
* leftcurrent == P_NONE && btpo_prev != P_NONE when the left sibling
837+
* of the parent's low-key downlink is half-dead. (A half-dead page
838+
* has no downlink from its parent.) Under heavyweight locking, the
839+
* last bt_leftmost_ignoring_half_dead() validated this btpo_prev.
840+
* Without heavyweight locking, validation of the P_NONE case remains
841+
* unimplemented.
842+
*/
843+
if (opaque->btpo_prev!=leftcurrent&&leftcurrent!=P_NONE)
833844
bt_recheck_sibling_links(state,opaque->btpo_prev,leftcurrent);
834845

835846
/* Check level */
@@ -910,6 +921,66 @@ bt_check_level_from_leftmost(BtreeCheckState *state, BtreeLevel level)
910921
returnnextleveldown;
911922
}
912923

924+
/*
925+
* Like P_LEFTMOST(start_opaque), but accept an arbitrarily-long chain of
926+
* half-dead, sibling-linked pages to the left. If a half-dead page appears
927+
* under state->readonly, the database exited recovery between the first-stage
928+
* and second-stage WAL records of a deletion.
929+
*/
930+
staticbool
931+
bt_leftmost_ignoring_half_dead(BtreeCheckState*state,
932+
BlockNumberstart,
933+
BTPageOpaquestart_opaque)
934+
{
935+
BlockNumberreached=start_opaque->btpo_prev,
936+
reached_from=start;
937+
boolall_half_dead= true;
938+
939+
/*
940+
* To handle the !readonly case, we'd need to accept BTP_DELETED pages and
941+
* potentially observe nbtree/README "Page deletion and backwards scans".
942+
*/
943+
Assert(state->readonly);
944+
945+
while (reached!=P_NONE&&all_half_dead)
946+
{
947+
Pagepage=palloc_btree_page(state,reached);
948+
BTPageOpaquereached_opaque= (BTPageOpaque)PageGetSpecialPointer(page);
949+
950+
CHECK_FOR_INTERRUPTS();
951+
952+
/*
953+
* Try to detect btpo_prev circular links. _bt_unlink_halfdead_page()
954+
* writes that side-links will continue to point to the siblings.
955+
* Check btpo_next for that property.
956+
*/
957+
all_half_dead=P_ISHALFDEAD(reached_opaque)&&
958+
reached!=start&&
959+
reached!=reached_from&&
960+
reached_opaque->btpo_next==reached_from;
961+
if (all_half_dead)
962+
{
963+
XLogRecPtrpagelsn=PageGetLSN(page);
964+
965+
/* pagelsn should point to an XLOG_BTREE_MARK_PAGE_HALFDEAD */
966+
ereport(DEBUG1,
967+
(errcode(ERRCODE_NO_DATA),
968+
errmsg_internal("harmless interrupted page deletion detected in index \"%s\"",
969+
RelationGetRelationName(state->rel)),
970+
errdetail_internal("Block=%u right block=%u page lsn=%X/%X.",
971+
reached,reached_from,
972+
LSN_FORMAT_ARGS(pagelsn))));
973+
974+
reached_from=reached;
975+
reached=reached_opaque->btpo_prev;
976+
}
977+
978+
pfree(page);
979+
}
980+
981+
returnall_half_dead;
982+
}
983+
913984
/*
914985
* Raise an error when target page's left link does not point back to the
915986
* previous target page, called leftcurrent here. The leftcurrent page's
@@ -950,6 +1021,9 @@ bt_recheck_sibling_links(BtreeCheckState *state,
9501021
BlockNumberbtpo_prev_from_target,
9511022
BlockNumberleftcurrent)
9521023
{
1024+
/* taking BTPageOpaque from metapage would give irrelevant findings */
1025+
Assert(leftcurrent!=P_NONE);
1026+
9531027
if (!state->readonly)
9541028
{
9551029
Bufferlbuf;
@@ -1933,7 +2007,8 @@ bt_child_highkey_check(BtreeCheckState *state,
19332007
opaque= (BTPageOpaque)PageGetSpecialPointer(page);
19342008

19352009
/* The first page we visit at the level should be leftmost */
1936-
if (first&& !BlockNumberIsValid(state->prevrightlink)&& !P_LEFTMOST(opaque))
2010+
if (first&& !BlockNumberIsValid(state->prevrightlink)&&
2011+
!bt_leftmost_ignoring_half_dead(state,blkno,opaque))
19372012
ereport(ERROR,
19382013
(errcode(ERRCODE_INDEX_CORRUPTED),
19392014
errmsg("the first child of leftmost target page is not leftmost of its level in index \"%s\"",

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