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/20200202161718.GI13621@telsasoft.com
Backpatch-through: 9.5

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 820041175221d80e40d1d9f2ee7ba5ae4a4e0dc2..f1daf4b148439ce462af3a3d9f949af887fb2012 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -167,6 +167,7 @@ typedef struct AlteredTableInfo
        List       *changedIndexOids;           /* OIDs of indexes to rebuild */
        List       *changedIndexDefs;           /* string definitions of same */
        char       *replicaIdentityIndex;       /* index to reset as REPLICA IDENTITY */
+       char       *clusterOnIndex;     /* index to use for CLUSTER */
 } AlteredTableInfo;
 
 /* Struct describing one new constraint to check in Phase 3 scan */
@@ -8583,6 +8584,21 @@ RememberReplicaIdentityForRebuilding(Oid indoid, AlteredTableInfo *tab)
        tab->replicaIdentityIndex = get_rel_name(indoid);
 }
 
+/*
+ * Subroutine for ATExecAlterColumnType: remember any clustered index.
+ */
+static void
+RememberClusterOnForRebuilding(Oid indoid, AlteredTableInfo *tab)
+{
+       if (!get_index_isclustered(indoid))
+               return;
+
+       if (tab->clusterOnIndex)
+               elog(ERROR, "relation %u has multiple clustered indexes", tab->relid);
+
+       tab->clusterOnIndex = get_rel_name(indoid);
+}
+
 /*
  * Subroutine for ATExecAlterColumnType: remember that a constraint needs
  * to be rebuilt (which we might already know).
@@ -8627,9 +8643,18 @@ RememberConstraintForRebuilding(Oid conoid, AlteredTableInfo *tab,
                                                                                                 defstring);
                }
 
+               /*
+                * For the index of a constraint, if any, remember if it is used for
+                * the table's replica identity or if it is a clustered index, so that
+                * ATPostAlterTypeCleanup() can queue up commands necessary to restore
+                * those properties.
+                */
                indoid = get_constraint_index(conoid);
                if (OidIsValid(indoid))
+               {
                        RememberReplicaIdentityForRebuilding(indoid, tab);
+                       RememberClusterOnForRebuilding(indoid, tab);
+               }
        }
 }
 
@@ -8674,7 +8699,13 @@ RememberIndexForRebuilding(Oid indoid, AlteredTableInfo *tab)
                        tab->changedIndexDefs = lappend(tab->changedIndexDefs,
                                                                                        defstring);
 
+                       /*
+                        * Remember if this index is used for the table's replica identity
+                        * or if it is a clustered index, so that ATPostAlterTypeCleanup()
+                        * can queue up commands necessary to restore those properties.
+                        */
                        RememberReplicaIdentityForRebuilding(indoid, tab);
+                       RememberClusterOnForRebuilding(indoid, tab);
                }
        }
 }
@@ -8886,6 +8917,21 @@ ATPostAlterTypeCleanup(List **wqueue, AlteredTableInfo *tab, LOCKMODE lockmode)
                        lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
        }
 
+       /*
+        * Queue up command to restore marking of index used for cluster.
+        */
+       if (tab->clusterOnIndex)
+       {
+               AlterTableCmd *cmd = makeNode(AlterTableCmd);
+
+               cmd->subtype = AT_ClusterOn;
+               cmd->name = tab->clusterOnIndex;
+
+               /* do it after indexes and constraints */
+               tab->subcmds[AT_PASS_OLD_CONSTR] =
+                       lappend(tab->subcmds[AT_PASS_OLD_CONSTR], cmd);
+       }
+
        /*
         * Now we can drop the existing constraints and indexes --- constraints
         * first, since some of them might depend on the indexes.  In fact, we

diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 49bf69a82fd3b8932ea86277d421242c0a6e7887..628e417963675a3166145e69f3f2ecf3d3dcc9c9 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3070,3 +3070,26 @@ get_index_isreplident(Oid index_oid)
 
        return result;
 }
+
+/*
+ * get_index_isclustered
+ *
+ *             Given the index OID, return pg_index.indisclustered.
+ */
+bool
+get_index_isclustered(Oid index_oid)
+{
+       bool            isclustered;
+       HeapTuple       tuple;
+       Form_pg_index rd_index;
+
+       tuple = SearchSysCache1(INDEXRELID, ObjectIdGetDatum(index_oid));
+       if (!HeapTupleIsValid(tuple))
+               elog(ERROR, "cache lookup failed for index %u", index_oid);
+
+       rd_index = (Form_pg_index) GETSTRUCT(tuple);
+       isclustered = rd_index->indisclustered;
+       ReleaseSysCache(tuple);
+
+       return isclustered;
+}

diff --git a/src/include/utils/lsyscache.h b/src/include/utils/lsyscache.h
index f01934afa143bbe0deede487aa1479d43e2c2403..211c54a2cad1ed96b4729eeb4c542041a46c12b5 100644 (file)
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -159,6 +159,7 @@ extern char *get_namespace_name_or_temp(Oid nspid);
 extern Oid     get_range_subtype(Oid rangeOid);
 extern Oid     get_range_collation(Oid rangeOid);
 extern bool    get_index_isreplident(Oid index_oid);
+extern bool get_index_isclustered(Oid index_oid);
 
 #define type_is_array(typid)  (get_element_type(typid) != InvalidOid)
 /* type_is_array_domain accepts both plain arrays and domains over arrays */

diff --git a/src/test/regress/expected/alter_table.out b/src/test/regress/expected/alter_table.out
index 075637ce56d86c84f1196f0bdebe3b02e1dc147d..46402b4a6d3a816a72459ee42c086022ddcbf206 100644 (file)
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -3109,3 +3109,51 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
 DROP TABLE logged3;
 DROP TABLE logged2;
 DROP TABLE logged1;
+-- Test that ALTER TABLE rewrite preserves a clustered index
+-- for normal indexes and indexes on constraints.
+create table alttype_cluster (a int);
+alter table alttype_cluster add primary key (a);
+create index alttype_cluster_ind on alttype_cluster (a);
+alter table alttype_cluster cluster on alttype_cluster_ind;
+-- Normal index remains clustered.
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+      indexrelid      | indisclustered 
+----------------------+----------------
+ alttype_cluster_ind  | t
+ alttype_cluster_pkey | f
+(2 rows)
+
+alter table alttype_cluster alter a type bigint;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+      indexrelid      | indisclustered 
+----------------------+----------------
+ alttype_cluster_ind  | t
+ alttype_cluster_pkey | f
+(2 rows)
+
+-- Constraint index remains clustered.
+alter table alttype_cluster cluster on alttype_cluster_pkey;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+      indexrelid      | indisclustered 
+----------------------+----------------
+ alttype_cluster_ind  | f
+ alttype_cluster_pkey | t
+(2 rows)
+
+alter table alttype_cluster alter a type int;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+      indexrelid      | indisclustered 
+----------------------+----------------
+ alttype_cluster_ind  | f
+ alttype_cluster_pkey | t
+(2 rows)
+
+drop table alttype_cluster;

diff --git a/src/test/regress/sql/alter_table.sql b/src/test/regress/sql/alter_table.sql
index 5f06a768545ded5a82830b3cdc11747152a097c4..421d4c7d3127bc5bdfbccef7522a4267adca1fc4 100644 (file)
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -1932,3 +1932,28 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
 DROP TABLE logged3;
 DROP TABLE logged2;
 DROP TABLE logged1;
+
+-- Test that ALTER TABLE rewrite preserves a clustered index
+-- for normal indexes and indexes on constraints.
+create table alttype_cluster (a int);
+alter table alttype_cluster add primary key (a);
+create index alttype_cluster_ind on alttype_cluster (a);
+alter table alttype_cluster cluster on alttype_cluster_ind;
+-- Normal index remains clustered.
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+alter table alttype_cluster alter a type bigint;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+-- Constraint index remains clustered.
+alter table alttype_cluster cluster on alttype_cluster_pkey;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+alter table alttype_cluster alter a type int;
+select indexrelid::regclass, indisclustered from pg_index
+  where indrelid = 'alttype_cluster'::regclass
+  order by indexrelid::regclass::text;
+drop table alttype_cluster;