Fix assorted silliness in ATExecSetCompression().

It's not okay to scribble directly on a syscache entry.
Nor to continue accessing said entry after releasing it.

Also get rid of not-used local variables.

Per valgrind testing.

diff --git a/src/backend/commands/tablecmds.c b/src/backend/commands/tablecmds.c
index 9b2800bf5e2f1cbf55c1b085961640ff2a96fc09..877c08814e0772b80f44cbceda833e8c756dbd8f 100644 (file)
--- a/src/backend/commands/tablecmds.c
+++ b/src/backend/commands/tablecmds.c
@@ -15071,9 +15071,6 @@ ATExecSetCompression(AlteredTableInfo *tab,
        char       *compression;
        char            typstorage;
        Oid                     cmoid;
-       Datum           values[Natts_pg_attribute];
-       bool            nulls[Natts_pg_attribute];
-       bool            replace[Natts_pg_attribute];
        ObjectAddress address;
 
        Assert(IsA(newValue, String));
@@ -15081,7 +15078,8 @@ ATExecSetCompression(AlteredTableInfo *tab,
 
        attrel = table_open(AttributeRelationId, RowExclusiveLock);
 
-       tuple = SearchSysCacheAttName(RelationGetRelid(rel), column);
+       /* copy the cache entry so we can scribble on it below */
+       tuple = SearchSysCacheCopyAttName(RelationGetRelid(rel), column);
        if (!HeapTupleIsValid(tuple))
                ereport(ERROR,
                                (errcode(ERRCODE_UNDEFINED_COLUMN),
@@ -15105,32 +15103,32 @@ ATExecSetCompression(AlteredTableInfo *tab,
                                        errmsg("column data type %s does not support compression",
                                                format_type_be(atttableform->atttypid))));
 
-       /* initialize buffers for new tuple values */
-       memset(values, 0, sizeof(values));
-       memset(nulls, false, sizeof(nulls));
-       memset(replace, false, sizeof(replace));
-
        /* get the attribute compression method. */
        cmoid = GetAttributeCompression(atttableform, compression);
 
+       /* update pg_attribute entry */
        atttableform->attcompression = cmoid;
        CatalogTupleUpdate(attrel, &tuple->t_self, tuple);
 
        InvokeObjectPostAlterHook(RelationRelationId,
                                                          RelationGetRelid(rel),
-                                                         atttableform->attnum);
-
-       ReleaseSysCache(tuple);
+                                                         attnum);
 
-       /* apply changes to the index column as well */
+       /*
+        * Apply the change to indexes as well (only for simple index columns,
+        * matching behavior of index.c ConstructTupleDescriptor()).
+        */
        SetIndexStorageProperties(rel, attrel, attnum, cmoid, '\0', lockmode);
+
+       heap_freetuple(tuple);
+
        table_close(attrel, RowExclusiveLock);
 
        /* make changes visible */
        CommandCounterIncrement();
 
        ObjectAddressSubSet(address, RelationRelationId,
-                                               RelationGetRelid(rel), atttableform->attnum);
+                                               RelationGetRelid(rel), attnum);
        return address;
 }