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Fix REPACK CONCURRENTLY for stored generated columns

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In order to replay concurrent changes, REPACK CONCURRENTLY needs the
pg_attrdef tuples for the transient table to be there, in case a tuple
is modified concurrently with REPACK and requires to store the value
from the generated column (which, with the current arrangements, means
all tuples concurrently updated or inserted).  Fix by creating a copy of
them from the original table.  Add a test that tickles the bug.

Author: Antonin Houska <ah@cybertec.at>
Reported-by: Ewan Young <kdbase.hack@gmail.com>
Diagnosed-by: Ewan Young <kdbase.hack@gmail.com>
Reviewed-by: Ewan Young <kdbase.hack@gmail.com>
Backpatch-through: 19
Discussion: https://postgr.es/m/CAON2xHMrELwx9vKg6niSf8fMBA=-MGXmG=MPQU6+vMVhGjF8kQ@mail.gmail.com
This commit is contained in:
Álvaro Herrera 2026-07-03 12:22:37 +02:00
parent 7afa11feca
commit 3be823486f
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GPG key ID: 1C20ACB9D5C564AE
2 changed files with 104 additions and 2 deletions
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103
src/backend/commands/repack.c
View file

@ -48,6 +48,7 @@
#include "catalog/namespace.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_am.h"
#include "catalog/pg_attrdef.h"
#include "catalog/pg_constraint.h"
#include "catalog/pg_inherits.h"
#include "catalog/toasting.h"
@ -204,6 +205,7 @@ static void rebuild_relation_finish_concurrent(Relation NewHeap, Relation OldHea
static List *build_new_indexes(Relation NewHeap, Relation OldHeap, List *OldIndexes);
static void copy_index_constraints(Relation old_index, Oid new_index_id,
Oid new_heap_id);
static void copy_attribute_defaults(Oid old_heap_oid, Oid new_heap_oid);
static Relation process_single_relation(RepackStmt *stmt,
LOCKMODE lockmode,
bool isTopLevel,
@ -1083,6 +1085,13 @@ rebuild_relation(Relation OldHeap, Relation index, bool verbose,
Assert(CheckRelationOidLockedByMe(OIDNewHeap, AccessExclusiveLock, false));
NewHeap = table_open(OIDNewHeap, NoLock);
/*
* In concurrent mode, create a copy of the attribute defaults on the temp
* table, which the executor needs when replaying concurrent data changes.
*/
if (concurrent)
copy_attribute_defaults(tableOid, OIDNewHeap);
/* Copy the heap data into the new table in the desired order */
copy_table_data(NewHeap, OldHeap, index, snapshot, verbose,
&swap_toast_by_content, &frozenXid, &cutoffMulti);
@ -3370,7 +3379,7 @@ build_new_indexes(Relation NewHeap, Relation OldHeap, List *OldIndexes)
*
* We don't need the constraints for anything else (the original constraints
* will be there once repack completes), so we add pg_depend entries so that
* the are dropped when the transient table is dropped.
* they are dropped when the transient table is dropped.
*/
static void
copy_index_constraints(Relation old_index, Oid new_index_id, Oid new_heap_id)
@ -3434,6 +3443,98 @@ copy_index_constraints(Relation old_index, Oid new_index_id, Oid new_heap_id)
CommandCounterIncrement();
}
/*
* Create a transient copy of attribute defaults.
*
* When repacking a table that has stored generated columns, the executor
* relies on these entries to generate the values for them during apply of
* concurrent operations. These copies are there to support that.
*
* We don't need the defaults for anything else, so we add pg_depend entries
* so that they are dropped when the transient table is dropped.
*/
static void
copy_attribute_defaults(Oid old_heap_oid, Oid new_heap_oid)
{
ScanKeyData skey;
Relation rel;
Relation att_rel;
SysScanDesc scan;
HeapTuple def_tup;
ObjectAddress objrel;
rel = table_open(AttrDefaultRelationId, RowExclusiveLock);
att_rel = table_open(AttributeRelationId, RowExclusiveLock);
ObjectAddressSet(objrel, RelationRelationId, new_heap_oid);
ScanKeyInit(&skey,
Anum_pg_attrdef_adrelid,
BTEqualStrategyNumber, F_OIDEQ,
ObjectIdGetDatum(old_heap_oid));
scan = systable_beginscan(rel, AttrDefaultIndexId, true,
NULL, 1, &skey);
while (HeapTupleIsValid(def_tup = systable_getnext(scan)))
{
Form_pg_attrdef adform;
Oid oid;
Datum def_values[Natts_pg_attrdef];
bool def_nulls[Natts_pg_attrdef];
bool def_replaces[Natts_pg_attrdef] = {0};
Datum att_values[Natts_pg_attribute];
bool att_nulls[Natts_pg_attribute];
bool att_replaces[Natts_pg_attribute] = {0};
HeapTuple new_def_tup,
att_tup,
new_att_tup;
ObjectAddress objad;
adform = (Form_pg_attrdef) GETSTRUCT(def_tup);
Assert(adform->adrelid == old_heap_oid);
/*
* Insert a new tuple that's identical to the existing one, other than
* its OID and the relation it refers to.
*/
oid = GetNewOidWithIndex(rel, AttrDefaultOidIndexId,
Anum_pg_attrdef_oid);
def_values[Anum_pg_attrdef_oid - 1] = ObjectIdGetDatum(oid);
def_nulls[Anum_pg_attrdef_oid - 1] = false;
def_replaces[Anum_pg_attrdef_oid - 1] = true;
def_values[Anum_pg_attrdef_adrelid - 1] = ObjectIdGetDatum(new_heap_oid);
def_nulls[Anum_pg_attrdef_adrelid - 1] = false;
def_replaces[Anum_pg_attrdef_adrelid - 1] = true;
new_def_tup = heap_modify_tuple(def_tup, RelationGetDescr(rel),
def_values, def_nulls, def_replaces);
CatalogTupleInsert(rel, new_def_tup);
/* Set atthasdef for this attribute in the transient table */
att_tup = SearchSysCache2(ATTNUM,
ObjectIdGetDatum(new_heap_oid),
ObjectIdGetDatum(adform->adnum));
if (!HeapTupleIsValid(att_tup))
elog(ERROR, "cache lookup failed for attribute %d of relation %u",
adform->adnum, new_heap_oid);
att_values[Anum_pg_attribute_atthasdef - 1] = BoolGetDatum(true);
att_nulls[Anum_pg_attribute_atthasdef - 1] = false;
att_replaces[Anum_pg_attribute_atthasdef - 1] = true;
new_att_tup = heap_modify_tuple(att_tup, RelationGetDescr(att_rel),
att_values, att_nulls, att_replaces);
CatalogTupleUpdate(att_rel, &new_att_tup->t_self, new_att_tup);
ReleaseSysCache(att_tup);
/* Add a pg_depend record so it's removed with the transient table */
ObjectAddressSet(objad, AttrDefaultRelationId, oid);
recordDependencyOn(&objad, &objrel, DEPENDENCY_AUTO);
}
systable_endscan(scan);
table_close(rel, RowExclusiveLock);
table_close(att_rel, RowExclusiveLock);
CommandCounterIncrement();
}
/*
* Try to start a background worker to perform logical decoding of data
* changes applied to relation while REPACK CONCURRENTLY is copying its

3
src/test/modules/injection_points/specs/repack.spec
View file

@ -3,7 +3,8 @@ setup
{
CREATE EXTENSION injection_points;
CREATE TABLE repack_test(i int PRIMARY KEY, j int);
CREATE TABLE repack_test(i int PRIMARY KEY, j int,
k int GENERATED ALWAYS AS (j * 2) STORED);
INSERT INTO repack_test(i, j) VALUES (1, 1), (2, 2), (3, 3), (4, 4);
CREATE TABLE relfilenodes(node oid);