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 03720887e7078eeb54db112907ba876ecd8013cb..8ca2ab13eb4bf7ce983c3c48cbb9c0168b92fb73 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -169,6 +169,7 @@ 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 */
@@ -8613,6 +8614,21 @@ 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).
@@ -8657,9 +8673,18 @@ 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);
+       }
    }
 }
 
@@ -8704,7 +8729,13 @@ 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);
        }
    }
 }
@@ -8916,6 +8947,21 @@ 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 5cf32e017853a154730bd2467470f5c00f1f1078..00b7c32e28b4fdd4c199f02af4ec849c09c823dd 100644 (file)
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -3113,3 +3113,26 @@ 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 6593cf03a527b55d478579eff13089a9135127bb..b41e446ad77fdd3b7df6a4325178e17abdeab9e1 100644 (file)
--- a/src/include/utils/lsyscache.h
+++ b/src/include/utils/lsyscache.h
@@ -161,6 +161,7 @@ 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 7403f95663e388cc63001df421d6a6d7e2d7779b..41db07911ede9440f4edab72462bc44fd2bfc9f5 100644 (file)
--- a/src/test/regress/expected/alter_table.out
+++ b/src/test/regress/expected/alter_table.out
@@ -3286,3 +3286,51 @@ Table "public.test_add_column"
  c4     | integer | 
 
 DROP TABLE test_add_column;
+-- 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 0e03c3e7ac9eaa1ae31fbb15a5cbf80afad58980..584efd33d1240bd519af8f40bde734a88f20e0be 100644 (file)
--- a/src/test/regress/sql/alter_table.sql
+++ b/src/test/regress/sql/alter_table.sql
@@ -2021,3 +2021,28 @@ ALTER TABLE test_add_column
    ADD COLUMN c4 integer;
 \d test_add_column
 DROP TABLE test_add_column;
+
+-- 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;