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Preserve clustered index after rewrites with ALTER TABLE
A table rewritten by ALTER TABLE would lose tracking of an index usable for CLUSTER. This setting is tracked by pg_index.indisclustered and is controlled by ALTER TABLE, so some extra work was needed to restore it properly. Note that ALTER TABLE only marks the index that can be used for clustering, and does not do the actual operation. Author: Amit Langote, Justin Pryzby Reviewed-by: Ibrar Ahmed, Michael Paquier Discussion: https://postgr.es/m/[email protected] Backpatch-through: 9.5
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‎src/backend/commands/tablecmds.c

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Original file line numberDiff line numberDiff line change
@@ -176,6 +176,7 @@ typedef struct AlteredTableInfo
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List *changedIndexOids; /* OIDs of indexes to rebuild */
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List *changedIndexDefs; /* string definitions of same */
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char *replicaIdentityIndex; /* index to reset as REPLICA IDENTITY */
179+
char *clusterOnIndex; /* index to use for CLUSTER */
179180
} AlteredTableInfo;
180181

181182
/* Struct describing one new constraint to check in Phase 3 scan */
@@ -10331,6 +10332,21 @@ RememberReplicaIdentityForRebuilding(Oid indoid, AlteredTableInfo *tab)
1033110332
tab->replicaIdentityIndex = get_rel_name(indoid);
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}
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10335+
/*
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* Subroutine for ATExecAlterColumnType: remember any clustered index.
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*/
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static void
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RememberClusterOnForRebuilding(Oid indoid, AlteredTableInfo *tab)
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{
10341+
if (!get_index_isclustered(indoid))
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return;
10343+
10344+
if (tab->clusterOnIndex)
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elog(ERROR, "relation %u has multiple clustered indexes", tab->relid);
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10347+
tab->clusterOnIndex = get_rel_name(indoid);
10348+
}
10349+
1033410350
/*
1033510351
* Subroutine for ATExecAlterColumnType: remember that a constraint needs
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* to be rebuilt (which we might already know).
@@ -10356,9 +10372,18 @@ RememberConstraintForRebuilding(Oid conoid, AlteredTableInfo *tab)
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tab->changedConstraintDefs = lappend(tab->changedConstraintDefs,
1035710373
defstring);
1035810374

10375+
/*
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* For the index of a constraint, if any, remember if it is used for
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* the table's replica identity or if it is a clustered index, so that
10378+
* ATPostAlterTypeCleanup() can queue up commands necessary to restore
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* those properties.
10380+
*/
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indoid = get_constraint_index(conoid);
1036010382
if (OidIsValid(indoid))
10383+
{
1036110384
RememberReplicaIdentityForRebuilding(indoid, tab);
10385+
RememberClusterOnForRebuilding(indoid, tab);
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}
1036210387
}
1036310388
}
1036410389

@@ -10402,7 +10427,13 @@ RememberIndexForRebuilding(Oid indoid, AlteredTableInfo *tab)
1040210427
tab->changedIndexDefs = lappend(tab->changedIndexDefs,
1040310428
defstring);
1040410429

10430+
/*
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* Remember if this index is used for the table's replica identity
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* or if it is a clustered index, so that ATPostAlterTypeCleanup()
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* can queue up commands necessary to restore those properties.
10434+
*/
1040510435
RememberReplicaIdentityForRebuilding(indoid, tab);
10436+
RememberClusterOnForRebuilding(indoid, tab);
1040610437
}
1040710438
}
1040810439
}
@@ -10635,6 +10666,21 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
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lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
1063610667
}
1063710668

10669+
/*
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* Queue up command to restore marking of index used for cluster.
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*/
10672+
if (tab->clusterOnIndex)
10673+
{
10674+
AlterTableCmd *cmd = makeNode(AlterTableCmd);
10675+
10676+
cmd->subtype = AT_ClusterOn;
10677+
cmd->name = tab->clusterOnIndex;
10678+
10679+
/* do it after indexes and constraints */
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tab->subcmds[AT_PASS_OLD_CONSTR] =
10681+
lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
10682+
}
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1063810684
/*
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* It should be okay to use DROP_RESTRICT here, since nothing else should
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* be depending on these objects.

‎src/backend/utils/cache/lsyscache.c

Lines changed: 23 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3181,3 +3181,26 @@ get_index_isreplident(Oid index_oid)
31813181

31823182
return result;
31833183
}
3184+
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/*
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* get_index_isclustered
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*
3188+
* Given the index OID, return pg_index.indisclustered.
3189+
*/
3190+
bool
3191+
get_index_isclustered(Oid index_oid)
3192+
{
3193+
bool isclustered;
3194+
HeapTuple tuple;
3195+
Form_pg_index rd_index;
3196+
3197+
tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
3198+
if (!HeapTupleIsValid(tuple))
3199+
elog(ERROR, "cache lookup failed for index %u", index_oid);
3200+
3201+
rd_index = (Form_pg_index) GETSTRUCT(tuple);
3202+
isclustered = rd_index->indisclustered;
3203+
ReleaseSysCache(tuple);
3204+
3205+
return isclustered;
3206+
}

‎src/include/utils/lsyscache.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -179,6 +179,7 @@ extern char *get_namespace_name_or_temp(Oid nspid);
179179
extern Oid get_range_subtype(Oid rangeOid);
180180
extern Oid get_range_collation(Oid rangeOid);
181181
extern bool get_index_isreplident(Oid index_oid);
182+
extern bool get_index_isclustered(Oid index_oid);
182183

183184
#define type_is_array(typid) (get_element_type(typid) != InvalidOid)
184185
/* type_is_array_domain accepts both plain arrays and domains over arrays */

‎src/test/regress/expected/alter_table.out

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Original file line numberDiff line numberDiff line change
@@ -4212,3 +4212,51 @@ create trigger xtrig
42124212
update bar1 set a = a + 1;
42134213
INFO: a=1, b=1
42144214
/* End test case for bug #16242 */
4215+
-- Test that ALTER TABLE rewrite preserves a clustered index
4216+
-- for normal indexes and indexes on constraints.
4217+
create table alttype_cluster (a int);
4218+
alter table alttype_cluster add primary key (a);
4219+
create index alttype_cluster_ind on alttype_cluster (a);
4220+
alter table alttype_cluster cluster on alttype_cluster_ind;
4221+
-- Normal index remains clustered.
4222+
select indexrelid::regclass, indisclustered from pg_index
4223+
where indrelid = 'alttype_cluster'::regclass
4224+
order by indexrelid::regclass::text;
4225+
indexrelid | indisclustered
4226+
----------------------+----------------
4227+
alttype_cluster_ind | t
4228+
alttype_cluster_pkey | f
4229+
(2 rows)
4230+
4231+
alter table alttype_cluster alter a type bigint;
4232+
select indexrelid::regclass, indisclustered from pg_index
4233+
where indrelid = 'alttype_cluster'::regclass
4234+
order by indexrelid::regclass::text;
4235+
indexrelid | indisclustered
4236+
----------------------+----------------
4237+
alttype_cluster_ind | t
4238+
alttype_cluster_pkey | f
4239+
(2 rows)
4240+
4241+
-- Constraint index remains clustered.
4242+
alter table alttype_cluster cluster on alttype_cluster_pkey;
4243+
select indexrelid::regclass, indisclustered from pg_index
4244+
where indrelid = 'alttype_cluster'::regclass
4245+
order by indexrelid::regclass::text;
4246+
indexrelid | indisclustered
4247+
----------------------+----------------
4248+
alttype_cluster_ind | f
4249+
alttype_cluster_pkey | t
4250+
(2 rows)
4251+
4252+
alter table alttype_cluster alter a type int;
4253+
select indexrelid::regclass, indisclustered from pg_index
4254+
where indrelid = 'alttype_cluster'::regclass
4255+
order by indexrelid::regclass::text;
4256+
indexrelid | indisclustered
4257+
----------------------+----------------
4258+
alttype_cluster_ind | f
4259+
alttype_cluster_pkey | t
4260+
(2 rows)
4261+
4262+
drop table alttype_cluster;

‎src/test/regress/sql/alter_table.sql

Lines changed: 25 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2802,3 +2802,28 @@ create trigger xtrig
28022802
update bar1 set a = a + 1;
28032803

28042804
/* End test case for bug #16242 */
2805+
2806+
-- Test that ALTER TABLE rewrite preserves a clustered index
2807+
-- for normal indexes and indexes on constraints.
2808+
create table alttype_cluster (a int);
2809+
alter table alttype_cluster add primary key (a);
2810+
create index alttype_cluster_ind on alttype_cluster (a);
2811+
alter table alttype_cluster cluster on alttype_cluster_ind;
2812+
-- Normal index remains clustered.
2813+
select indexrelid::regclass, indisclustered from pg_index
2814+
where indrelid = 'alttype_cluster'::regclass
2815+
order by indexrelid::regclass::text;
2816+
alter table alttype_cluster alter a type bigint;
2817+
select indexrelid::regclass, indisclustered from pg_index
2818+
where indrelid = 'alttype_cluster'::regclass
2819+
order by indexrelid::regclass::text;
2820+
-- Constraint index remains clustered.
2821+
alter table alttype_cluster cluster on alttype_cluster_pkey;
2822+
select indexrelid::regclass, indisclustered from pg_index
2823+
where indrelid = 'alttype_cluster'::regclass
2824+
order by indexrelid::regclass::text;
2825+
alter table alttype_cluster alter a type int;
2826+
select indexrelid::regclass, indisclustered from pg_index
2827+
where indrelid = 'alttype_cluster'::regclass
2828+
order by indexrelid::regclass::text;
2829+
drop table alttype_cluster;

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