From feedb5704826a09d32cbd57989f108a491290228 Mon Sep 17 00:00:00 2001 From: jian he Date: Thu, 16 Jul 2026 16:52:09 +0800 Subject: [PATCH v15 1/1] using indexscan to speedup add not null constraints This patch tries to use index_beginscan() / index_getnext() / index_endscan() mentioned in [1] to speedup adding not-null constraints to the existing table. The main logic happens in phase3 ATRewriteTable 1. collect all not-null constraints. 2. For each not-null constraint, check whether there is a corresponding index available for validation. If not, then cannot use indexscan mechanism to verify not-null constraints. 3. If any of the following conditions are true * table scan or rewrite is required, * table wasn't locked with `AccessExclusiveLock` * the NOT NULL constraint applies to a virtual generated column then index scan cannot be used for fast validation. If all conditions are satisfied, attempt to use indexscan to verify whether the column contains any NULL values. concurrency concern: ALTER TABLE SET NOT NULL will take an ACCESS EXCLUSIVE lock, so there is less variant of racing issue can occur. see[2] references: [1] https://postgr.es/m/CA%2BTgmoa5NKz8iGW_9v7wz%3D-%2BzQFu%3DE4SZoaTaU1znLaEXRYp-Q%40mail.gmail.com [2] https://postgr.es/m/900056D1-32DF-4927-8251-3E0C0DC407FD%40anarazel.de discussion: https://postgr.es/m/CACJufxFiW=4k1is=F1J=r-Cx1RuByXQPUrWB331U47rSnGz+hw@mail.gmail.com commitfest entry: https://commitfest.postgresql.org/patch/5444 --- src/backend/commands/tablecmds.c | 305 +++++++++++++++++- src/test/modules/test_misc/meson.build | 1 + .../t/015_indexscan_validate_notnull.pl | 145 +++++++++ 3 files changed, 446 insertions(+), 5 deletions(-) create mode 100644 src/test/modules/test_misc/t/015_indexscan_validate_notnull.pl diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c index cb93c3e935a..9e4e557d29d 100644 --- a/src/backend/commands/tablecmds.c +++ b/src/backend/commands/tablecmds.c @@ -213,16 +213,19 @@ typedef struct AlteredTableInfo List *changedStatisticsDefs; /* string definitions of same */ } AlteredTableInfo; -/* Struct describing one new constraint to check in Phase 3 scan */ -/* Note: new not-null constraints are handled elsewhere */ +/* + * Struct describing one new constraint to check in Phase 3 scan. Note: new + * not-null constraints were also added to Phase3. +*/ typedef struct NewConstraint { char *name; /* Constraint name, or NULL if none */ - ConstrType contype; /* CHECK or FOREIGN */ + ConstrType contype; /* CHECK or FOREIGN or NOT NULL */ Oid refrelid; /* PK rel, if FOREIGN */ Oid refindid; /* OID of PK's index, if FOREIGN */ bool conwithperiod; /* Whether the new FOREIGN KEY uses PERIOD */ Oid conid; /* OID of pg_constraint entry, if FOREIGN */ + int attnum; /* NOT NULL constraint attribute number */ Node *qual; /* Check expr or CONSTR_FOREIGN Constraint */ ExprState *qualstate; /* Execution state for CHECK expr */ } NewConstraint; @@ -794,6 +797,7 @@ static void ATExecSplitPartition(List **wqueue, AlteredTableInfo *tab, static List *collectPartitionIndexExtDeps(List *partitionOids); static void applyPartitionIndexExtDeps(Oid newPartOid, List *extDepState); static void freePartitionIndexExtDeps(List *extDepState); +static bool index_check_notnull(Relation relation, List *notnull_attnums); /* ---------------------------------------------------------------- * DefineRelation @@ -6312,6 +6316,9 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap) needscan = true; con->qualstate = ExecPrepareExpr((Expr *) expand_generated_columns_in_expr(con->qual, oldrel, 1), estate); break; + case CONSTR_NOTNULL: + /* Nothing to do here */ + break; case CONSTR_FOREIGN: /* Nothing to do here */ break; @@ -6339,6 +6346,78 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap) notnull_attrs = notnull_virtual_attrs = NIL; if (newrel || tab->verify_new_notnull) { + bool nullsChecked = false; + + /* + * The conditions for using indexscan mechanism fast verifying + * not-null constraints are quite strict. All of the following + * conditions must be met. + * + * 1. AlteredTableInfo->verify_new_notnull is true. + * + * 2. No table scan (e.g., for CHECK constraint verification) or table + * rewrite is expected later, if one is, using indexscan would just + * wastes cycles. + * + * 3. Indexes cannot be created on virtual generated columns, so fast + * checking not-null constraints is not applicable to them. + * + * 4. The relation must be a plain table. + * + * 5. To prevent possible concurrency issues, the table must already + * be locked with an AccessExclusiveLock, which is the lock obtained + * during ALTER TABLE SET NOT NULL. + */ + if (!needscan && + newrel == NULL && + oldrel->rd_rel->relkind == RELKIND_RELATION && + CheckRelationLockedByMe(oldrel, AccessExclusiveLock, false)) + { + List *notnull_attnums = NIL; + + Assert(!tab->rewrite); + + foreach(l, tab->constraints) + { + Form_pg_attribute attr; + NewConstraint *con = lfirst(l); + + if (con->contype != CONSTR_NOTNULL) + continue; + + attr = TupleDescAttr(newTupDesc, con->attnum - 1); + + if (attr->attisdropped) + continue; + + Assert(attr->attnotnull); + Assert(attr->attnum == con->attnum); + + if (attr->attgenerated == ATTRIBUTE_GENERATED_VIRTUAL) + { + needscan = true; + break; + } + + notnull_attnums = list_append_unique_int(notnull_attnums, + attr->attnum); + } + + if (!needscan) + { + if (index_check_notnull(oldrel, notnull_attnums)) + { + nullsChecked = true; + + ereport(DEBUG1, + errmsg_internal("all new not-null constraints on relation \"%s\" have been validated by using index scan", + RelationGetRelationName(oldrel))); + } + else + needscan = true; + } + } + /* * If we are rebuilding the tuples OR if we added any new but not * verified not-null constraints, check all *valid* not-null @@ -6349,7 +6428,7 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap) * not-null constraints over virtual generated columns; instead, they * are collected in notnull_virtual_attrs for verification elsewhere. */ - for (i = 0; i < newTupDesc->natts; i++) + for (i = 0; !nullsChecked && i < newTupDesc->natts; i++) { CompactAttribute *attr = TupleDescCompactAttr(newTupDesc, i); @@ -6367,6 +6446,9 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap) } if (notnull_attrs || notnull_virtual_attrs) needscan = true; + + if (nullsChecked) + Assert(needscan == false); } if (newrel || needscan) @@ -8061,6 +8143,7 @@ ATExecSetNotNull(List **wqueue, Relation rel, char *conName, char *colName, CookedConstraint *ccon; List *cooked; bool is_no_inherit = false; + AlteredTableInfo *tab = ATGetQueueEntry(wqueue, rel); /* Guard against stack overflow due to overly deep inheritance tree. */ check_stack_depth(); @@ -8189,6 +8272,25 @@ ATExecSetNotNull(List **wqueue, Relation rel, char *conName, char *colName, cooked = AddRelationNewConstraints(rel, NIL, list_make1(constraint), false, !recursing, false, NULL); ccon = linitial(cooked); + + Assert(ccon->contype == CONSTR_NOTNULL); + + /* + * Add this to-be-validated not-null constraint to Phase 3's queue. We may + * able to use indexscan mechanism to verify this not-null constraint in + * Phase3. + */ + if (!ccon->skip_validation) + { + NewConstraint *newcon = palloc0_object(NewConstraint); + + newcon->name = ccon->name; + newcon->contype = CONSTR_NOTNULL; + newcon->attnum = ccon->attnum; + + tab->constraints = lappend(tab->constraints, newcon); + } + ObjectAddressSet(address, ConstraintRelationId, ccon->conoid); /* Mark pg_attribute.attnotnull for the column and queue validation */ @@ -10089,13 +10191,15 @@ ATAddCheckNNConstraint(List **wqueue, AlteredTableInfo *tab, Relation rel, { CookedConstraint *ccon = (CookedConstraint *) lfirst(lcon); - if (!ccon->skip_validation && ccon->contype != CONSTR_NOTNULL) + if (!ccon->skip_validation) { NewConstraint *newcon; newcon = palloc0_object(NewConstraint); newcon->name = ccon->name; newcon->contype = ccon->contype; + if (ccon->contype == CONSTR_NOTNULL) + newcon->attnum = ccon->attnum; newcon->qual = ccon->expr; tab->constraints = lappend(tab->constraints, newcon); @@ -13765,6 +13869,7 @@ QueueNNConstraintValidation(List **wqueue, Relation conrel, Relation rel, List *children = NIL; AttrNumber attnum; char *colname; + NewConstraint *newcon; con = (Form_pg_constraint) GETSTRUCT(contuple); Assert(con->contype == CONSTRAINT_NOTNULL); @@ -13829,6 +13934,20 @@ QueueNNConstraintValidation(List **wqueue, Relation conrel, Relation rel, set_attnotnull(NULL, rel, attnum, true, false); tab = ATGetQueueEntry(wqueue, rel); + + /* + * Queue validation for phase 3. ALTER TABLE SET NOT NULL adds a NOT NULL + * constraint (NewConstraint) to AlteredTableInfo->constraints; for + * consistency, we do the same here. This setup allows phase 3 + * (ATRewriteTable) to quickly validate the column's NULL status using an + * index scan, if all conditions are met. + */ + newcon = palloc0_object(NewConstraint); + newcon->name = colname; + newcon->contype = CONSTR_NOTNULL; + newcon->attnum = attnum; + tab->constraints = lappend(tab->constraints, newcon); + tab->verify_new_notnull = true; /* @@ -24390,3 +24509,179 @@ ATExecSplitPartition(List **wqueue, AlteredTableInfo *tab, Relation rel, /* Restore the userid and security context. */ SetUserIdAndSecContext(save_userid, save_sec_context); } + +/* + * notnull_attnums: list of attribute numbers for all newly added NOT NULL + * constraints. + * + * For each NOT NULL attribute, first check whether the relation has a suitable + * index to fetch that attribute content. If so, using indexscan to verify that + * attribute contains no NULL values. + * + * Returning true means the new NOT NULL constraints are fully verified and no + * extra table scans are necessary. + */ +static bool +index_check_notnull(Relation relation, List *notnull_attnums) +{ + SysScanDesc indscan; + ScanKeyData skey; + List *idxs = NIL; + List *attnums = NIL; + bool all_not_null = true; + ListCell *lc, + *lc2; + Relation pg_index; + Relation indexRel; + HeapTuple indexTuple; + + if (notnull_attnums == NIL) + return false; + + pg_index = table_open(IndexRelationId, AccessShareLock); + + /* Prepare to scan pg_index for entries having indrelid = this rel */ + ScanKeyInit(&skey, + Anum_pg_index_indrelid, + BTEqualStrategyNumber, + F_OIDEQ, + ObjectIdGetDatum(RelationGetRelid(relation))); + + indscan = systable_beginscan(pg_index, IndexIndrelidIndexId, true, + NULL, 1, &skey); + + while (HeapTupleIsValid(indexTuple = systable_getnext(indscan))) + { + Form_pg_attribute attr; + + Form_pg_index index = (Form_pg_index) GETSTRUCT(indexTuple); + + /* + * We only use non-deferred, valid, and live b-tree indexes to verify + * NOT NULL constraints. + */ + if (!index->indimmediate || !index->indisvalid || !index->indislive) + continue; + + /* cannot use expression index or partial index too */ + if (!heap_attisnull(indexTuple, Anum_pg_index_indexprs, NULL) || + !heap_attisnull(indexTuple, Anum_pg_index_indpred, NULL)) + continue; + + indexRel = index_open(index->indexrelid, AccessShareLock); + + if (indexRel->rd_rel->relam != BTREE_AM_OID) + { + index_close(indexRel, NoLock); + + continue; + } + + /* + * If the index is valid, but cannot yet be used, ignore it; See + * src/backend/access/heap/README.HOT for discussion. + */ + if (index->indcheckxmin && + !TransactionIdPrecedes(HeapTupleHeaderGetXmin(indexRel->rd_indextuple->t_data), + TransactionXmin)) + { + index_close(indexRel, NoLock); + continue; + } + + attr = TupleDescAttr(RelationGetDescr(relation), (index->indkey.values[0] - 1)); + + if (list_member_int(notnull_attnums, attr->attnum) && + !list_member_int(attnums, attr->attnum)) + { + attnums = lappend_int(attnums, attr->attnum); + idxs = lappend_oid(idxs, index->indexrelid); + } + + index_close(indexRel, NoLock); + } + systable_endscan(indscan); + table_close(pg_index, NoLock); + + /* + * Verify NOT NULL constraints using a suitable index, falling back to a + * full table scan if a suitable index is not present. + */ + if (attnums == NIL || + list_length(notnull_attnums) != list_length(attnums)) + return false; + + foreach_int(attno, notnull_attnums) + { + if (!list_member_int(attnums, attno)) + return false; + } + + forboth(lc, attnums, lc2, idxs) + { + SnapshotData DirtySnapshot; + IndexScanDesc indexScan; + ScanKeyData scankeys[INDEX_MAX_KEYS]; + AttrNumber sk_attno = -1; + AttrNumber attno = lfirst_int(lc); + Oid indexoid = lfirst_oid(lc2); + IndexInfo *indexInfo; + TupleTableSlot *existing_slot; + + indexRel = index_open(indexoid, NoLock); + indexInfo = BuildIndexInfo(indexRel); + existing_slot = table_slot_create(relation, NULL); + + /* + * Search the tuples that are in the index for any violations, + * including tuples that aren't visible yet. + */ + InitDirtySnapshot(DirtySnapshot); + + if (indexInfo->ii_IndexAttrNumbers[0] == attno) + sk_attno = 1; + else + elog(ERROR, "cache lookup failed for attribute number %d on index %u", + indexoid, attno); + + /* set up an IS NULL scan key so that we ignore not nulls */ + ScanKeyEntryInitialize(&scankeys[0], + SK_ISNULL | SK_SEARCHNULL, + sk_attno, /* index col to scan */ + InvalidStrategy, /* no strategy */ + InvalidOid, /* no strategy subtype */ + InvalidOid, /* no collation */ + InvalidOid, /* no reg proc for this */ + (Datum) 0); /* constant */ + + indexScan = index_beginscan(relation, + indexRel, + &DirtySnapshot, + NULL, + 1, + 0, + SO_NONE); + index_rescan(indexScan, scankeys, 1, NULL, 0); + + while (index_getnext_slot(indexScan, ForwardScanDirection, existing_slot)) + { + /* + * At this point, we have found that some attribute value is NULL. + * Since btree indexes are never lossy, no need recheck the NULL + * condition. + */ + all_not_null = false; + break; + } + + index_endscan(indexScan); + index_close(indexRel, NoLock); + ExecDropSingleTupleTableSlot(existing_slot); + + /* exit earlier */ + if (!all_not_null) + return false; + } + + return true; +} diff --git a/src/test/modules/test_misc/meson.build b/src/test/modules/test_misc/meson.build index ee290698b31..564b7d957ca 100644 --- a/src/test/modules/test_misc/meson.build +++ b/src/test/modules/test_misc/meson.build @@ -23,6 +23,7 @@ tests += { 't/012_ddlutils.pl', 't/013_temp_obj_multisession.pl', 't/014_log_statement_max_length.pl', + 't/015_indexscan_validate_notnull.pl', ], # The injection points are cluster-wide, so disable installcheck 'runningcheck': false, diff --git a/src/test/modules/test_misc/t/015_indexscan_validate_notnull.pl b/src/test/modules/test_misc/t/015_indexscan_validate_notnull.pl new file mode 100644 index 00000000000..5e14ae622d7 --- /dev/null +++ b/src/test/modules/test_misc/t/015_indexscan_validate_notnull.pl @@ -0,0 +1,145 @@ +# Copyright (c) 2026, PostgreSQL Global Development Group + +# Verify that indexscan mechanism can speedup ALTER TABLE ADD NOT NULL + +use strict; +use warnings FATAL => 'all'; + +use PostgreSQL::Test::Cluster; +use PostgreSQL::Test::Utils; +use Test::More; +use Time::HiRes qw(usleep); + +# Initialize a test cluster +my $node = PostgreSQL::Test::Cluster->new('primary'); +$node->init(); +# Turn message level up to DEBUG1 so that we get the messages we want to see +$node->append_conf('postgresql.conf', 'client_min_messages = DEBUG1'); +$node->start; + +# Run a SQL command and return psql's stderr (including debug messages) +sub run_sql_command +{ + my $sql = shift; + my $stderr; + + $node->psql( + 'postgres', + $sql, + stderr => \$stderr, + on_error_die => 1, + on_error_stop => 1); + return $stderr; +} + +# Verify that run_sql_command output confirms an index scan is used for the NOT NULL check. +sub is_indexscan_veritify_notnull +{ + my $output = shift; + return index($output, 'DEBUG: all new not-null constraints on relation') != -1; +} + +my $output; + +note "test alter table SET NOT NULL using indexscan with partitioned table"; + +run_sql_command( + 'CREATE TABLE tp_notnull ( + a int, b int, c int, d int, f1 int default 1, + f2 int default 2, f3 int default 3, f4 int default 4, f5 int default 5) PARTITION BY range(a); + CREATE TABLE tp_notnull_1 partition of tp_notnull for values from ( 1 ) to (10); + CREATE TABLE tp_notnull_2 partition of tp_notnull for values from ( 10 ) to (21); + INSERT INTO tp_notnull(a, b, c, d) SELECT g, g + 10, g + 15, g FROM generate_series(1,19) g; + CREATE INDEX ON tp_notnull(b); + CREATE INDEX ON tp_notnull(c); + CREATE INDEX ON tp_notnull(d); + CREATE INDEX ON tp_notnull(f1) INCLUDE (f2); + CREATE INDEX ON tp_notnull USING hash (f3 int4_ops); + '); + +# Using index scan for NOT NULL verification requires every not-null column must possess a suitable index +$output = run_sql_command( + 'ALTER TABLE tp_notnull ALTER COLUMN a SET NOT NULL, ADD CONSTRAINT c_nn NOT NULL c'); +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan to verify not-null constraints on table tp_notnull'); + +# All columns have index on it, OK +$output = run_sql_command( + 'ALTER TABLE tp_notnull ALTER COLUMN d SET NOT NULL, ALTER COLUMN c SET NOT NULL, ALTER COLUMN b SET NOT NULL;'); +ok(is_indexscan_veritify_notnull($output), + 'using indexscan to verify not-null constraints on column b, c, d'); +ok( $output =~ + m/all new not-null constraints on relation "tp_notnull_1" have been validated by using index scan/, + 'all newly added constraints proved by indexscan'); +ok( $output =~ + m/all new not-null constraints on relation "tp_notnull_2" have been validated by using index scan/, + 'all newly added constraints proved by indexscan'); + +run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN b DROP NOT NULL;'); +# Now using index scans on partitions to quickly verify NOT NULL constraints +$output = run_sql_command('ALTER TABLE tp_notnull_1 ALTER COLUMN b SET NOT NULL;'); +ok(is_indexscan_veritify_notnull($output), 'index scan verifies NOT NULL for column b'); + +run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN b DROP NOT NULL;'); +# Cannot use indexscan to verify not-null constraint if table rewrite happens +$output = run_sql_command( + 'ALTER TABLE tp_notnull ALTER COLUMN b SET NOT NULL, ALTER COLUMN b SET DATA TYPE bigint;' +); +ok(!is_indexscan_veritify_notnull($output), 'table rewrite on tp_notnull, cannot use indexscan to verify not-null constraints on it'); + +run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN d DROP NOT NULL'); + +# Cannot use indexscan because ALTER TABLE VALIDATE CONSTRAINT only hold +# ShareUpdateExclusiveLock lock on the table +run_sql_command('ALTER TABLE tp_notnull ADD CONSTRAINT tp_notnull_d NOT NULL d NOT VALID;'); +$output = run_sql_command( + 'ALTER TABLE tp_notnull VALIDATE CONSTRAINT tp_notnull_d;' +); +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan for ALTER TABLE VALIDATE CONSTRAINT command'); + +run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN d DROP NOT NULL; + ALTER TABLE tp_notnull ADD CONSTRAINT tp_notnull_d NOT NULL d NOT VALID;'); + +# OK, ALTER COLUMN SET NOT NULL acquires AccessExclusiveLock +$output = run_sql_command( + 'ALTER TABLE tp_notnull VALIDATE CONSTRAINT tp_notnull_d, ALTER COLUMN b SET NOT NULL;' +); +ok(is_indexscan_veritify_notnull($output), 'using indexscan to verify not-null constraints on column b, c, d'); + +# Indexscan mechanism to verify NOT NULL constraints cannot apply to index +# INCLUDE column +$output = run_sql_command( + 'ALTER TABLE tp_notnull ADD CONSTRAINT nnf4 NOT NULL f2;' +); +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan to validate not-null constraint on tp_notnull'); + +# Indexscan mechanism to verify NOT NULL constraints cannot apply to non-Btree index +$output = run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN f3 SET NOT NULL;'); +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan to validate not-null constraints on tp_notnull'); + +run_sql_command('CREATE INDEX ON tp_notnull USING btree (f4 int4_ops, f5 int4_ops)'); +# Indexscan mechanism to verify NOT NULL constraints only apply to leading column +$output = run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN f4 SET NOT NULL'); +ok(is_indexscan_veritify_notnull($output), 'cannot use indexscan to validate not-null constraints on tp_notnull'); + +$output = run_sql_command('ALTER TABLE tp_notnull ALTER COLUMN f5 SET NOT NULL'); +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan to validate not-null constraints on tp_notnull'); + +run_sql_command(' + create table t(id int, v int) with (autovacuum_enabled = false, fillfactor = 50); + insert into t values (1, NULL)' +); +run_sql_command(' + begin; + select count(*) from t; + update t set v = 5 where id = 1; + create index t_v_idx on t (v); + alter table t alter column v set not null; + commit;' +); +# t_v_idx has pg_index.indcheckxmin = true: its underlying tuple belongs to a +# HOT chain, so this index cannot be trusted to answer "is this column NULL" +ok(!is_indexscan_veritify_notnull($output), 'cannot use indexscan to validate not-null constraints on t'); + +$node->stop('fast'); + +done_testing(); \ No newline at end of file -- 2.34.1