I attach a version of my toast-slicing patch, against current CVS

(current as of a few hours ago.)

This patch:

1. Adds PG_GETARG_xxx_P_SLICE() macros and associated support routines.

2. Adds routines in src/backend/access/tuptoaster.c for fetching only
necessary chunks of a toasted value. (Modelled on latest changes to
assume chunks are returned in order).

3. Amends text_substr and bytea_substr to use new methods. It now
handles multibyte cases -and should still lead to a performance
improvement in the multibyte case where the substring is near the
beginning of the string.

4. Added new command: ALTER TABLE tabname ALTER COLUMN colname SET
STORAGE {PLAIN | EXTERNAL | EXTENDED | MAIN} to parser and documented in
alter-table.sgml. (NB I used ColId as the item type for the storage
mode string, rather than a new production - I hope this makes sense!).
All this does is sets attstorage for the specified column.

4. AlterTableAlterColumnStatistics is now AlterTableAlterColumnFlags and
handles both statistics and storage (it uses the subtype code to
distinguish). The previous version of my patch also re-arranged other
code in backend/commands/command.c but I have dropped that from this
patch.(I plan to return to it separately).

5. Documented new macros (and also the PG_GETARG_xxx_P_COPY macros) in
xfunc.sgml. ref/alter_table.sgml also contains documentation for ALTER
COLUMN SET STORAGE.

John Gray

1 files changed, 75 insertions, 20 deletions

diff --git a/src/backend/commands/command.c b/src/backend/commands/command.c
index eefbe269f30..e49c8ca3212 100644
--- a/src/backend/commands/command.c
+++ b/src/backend/commands/command.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.157 2002/03/02 21:39:22 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/Attic/command.c,v 1.158 2002/03/05 05:33:08 momjian Exp $
  *
  * NOTES
  *	  The PerformAddAttribute() code, like most of the relation
@@ -714,20 +714,27 @@ drop_default(Oid relid, int16 attnum)
 
 
 /*
- * ALTER TABLE ALTER COLUMN SET STATISTICS
+ * ALTER TABLE ALTER COLUMN SET STATISTICS / STORAGE
  */
 void
-AlterTableAlterColumnStatistics(const char *relationName,
+AlterTableAlterColumnFlags(const char *relationName,
 								bool inh, const char *colName,
-								Node *statsTarget)
+								Node *flagValue, const char *flagType)
 {
 	Relation	rel;
 	Oid			myrelid;
-	int			newtarget;
+	int			newtarget = 1;
+	char        newstorage = 'x';
+	char        *storagemode;
 	Relation	attrelation;
 	HeapTuple	tuple;
 
-	/* we allow this on system tables */
+	/* we allow statistics case for system tables */
+
+	if (*flagType =='M' && !allowSystemTableMods && IsSystemRelationName(relationName))
+		elog(ERROR, "ALTER TABLE: relation \"%s\" is a system catalog",
+			 relationName);
+
 #ifndef NO_SECURITY
 	if (!pg_ownercheck(GetUserId(), relationName, RELNAME))
 		elog(ERROR, "ALTER TABLE: permission denied");
@@ -742,6 +749,50 @@ AlterTableAlterColumnStatistics(const char *relationName,
 	myrelid = RelationGetRelid(rel);
 	heap_close(rel, NoLock);	/* close rel, but keep lock! */
 
+	
+	/*
+	 * Check the supplied parameters before anything else
+	 */
+	if (*flagType == 'S')           /*
+									 * STATISTICS
+									 */
+	{
+		Assert(IsA(flagValue, Integer));
+		newtarget = intVal(flagValue);
+		
+		/*
+		 * Limit target to sane range (should we raise an error instead?)
+		 */
+		if (newtarget < 0)
+			newtarget = 0;
+		else if (newtarget > 1000)
+			newtarget = 1000;
+	}
+	else if (*flagType == 'M')      /*
+									 * STORAGE
+									 */
+	{
+		Assert(IsA(flagValue, Value));
+		
+		storagemode = strVal(flagValue);
+		if (strcasecmp(storagemode, "plain") == 0)
+			newstorage = 'p';
+		else if (strcasecmp(storagemode, "external") == 0)
+			newstorage = 'e';
+		else if (strcasecmp(storagemode, "extended") == 0)
+			newstorage = 'x';
+		else if (strcasecmp(storagemode, "main") == 0)
+			newstorage = 'm';
+		else
+			elog(ERROR, "ALTER TABLE: \"%s\" storage not recognized",
+				 storagemode);
+	}
+	else
+	{
+		elog(ERROR, "ALTER TABLE: Invalid column flag: %c",
+			 (int) *flagType);
+	}
+
 	/*
 	 * Propagate to children if desired
 	 */
@@ -765,23 +816,14 @@ AlterTableAlterColumnStatistics(const char *relationName,
 			if (childrelid == myrelid)
 				continue;
 			rel = heap_open(childrelid, AccessExclusiveLock);
-			AlterTableAlterColumnStatistics(RelationGetRelationName(rel),
-											false, colName, statsTarget);
+			AlterTableAlterColumnFlags(RelationGetRelationName(rel),
+											false, colName, flagValue, flagType);
 			heap_close(rel, AccessExclusiveLock);
 		}
 	}
 
 	/* -= now do the thing on this relation =- */
 
-	Assert(IsA(statsTarget, Integer));
-	newtarget = intVal(statsTarget);
-
-	/* Limit target to sane range (should we raise an error instead?) */
-	if (newtarget < 0)
-		newtarget = 0;
-	else if (newtarget > 1000)
-		newtarget = 1000;
-
 	attrelation = heap_openr(AttributeRelationName, RowExclusiveLock);
 
 	tuple = SearchSysCacheCopy(ATTNAME,
@@ -795,9 +837,22 @@ AlterTableAlterColumnStatistics(const char *relationName,
 	if (((Form_pg_attribute) GETSTRUCT(tuple))->attnum < 0)
 		elog(ERROR, "ALTER TABLE: cannot change system attribute \"%s\"",
 			 colName);
-
-	((Form_pg_attribute) GETSTRUCT(tuple))->attstattarget = newtarget;
-
+	/*
+	 * Now change the appropriate field
+	 */
+	if (*flagType == 'S')
+		((Form_pg_attribute) GETSTRUCT(tuple))->attstattarget = newtarget;
+	else
+	{
+		if ((newstorage == 'p') ||
+			(((Form_pg_attribute) GETSTRUCT(tuple))->attlen == -1))
+			((Form_pg_attribute) GETSTRUCT(tuple))->attstorage = newstorage;
+		else
+		{
+			elog(ERROR,
+				 "ALTER TABLE: Fixed-length columns can only have storage \"plain\"");
+		}
+	}
 	simple_heap_update(attrelation, &tuple->t_self, tuple);
 
 	/* keep system catalog indices current */