The following small patch provides a couple of minor updates (against

CVS HEAD):

Amended "strings" regression test. TOAST tests now insert two values
with storage set to "external", to exercise properly the TOAST slice
routines which fetch only a subset of the chunks.

Changed now-misleading comment on AlterTableCreateToastTable in
tablecmds.c, because both columns of the index on a toast table are now
used.

John Gray

src/backend/commands/tablecmds.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.34 2002/08/27 03:56:34 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/commands/tablecmds.c,v 1.35 2002/08/28 20:18:29 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3417,12 +3417,13 @@ AlterTableCreateToastTable(Oid relOid, bool silent)
 	/*
 	 * Create unique index on chunk_id, chunk_seq.
 	 *
-	 * NOTE: the tuple toaster could actually function with a single-column
-	 * index on chunk_id only.	However, it couldn't be unique then.  We
-	 * want it to be unique as a check against the possibility of
-	 * duplicate TOAST chunk OIDs.	Too, the index might be a little more
-	 * efficient this way, since btree isn't all that happy with large
-	 * numbers of equal keys.
+	 * NOTE: the normal TOAST access routines could actually function with 
+	 * a single-column index on chunk_id only. However, the slice access
+	 * routines use both columns for faster access to an individual chunk.
+	 * In addition, we want it to be unique as a check against the 
+	 * possibility of duplicate TOAST chunk OIDs. The index might also be
+	 * a little more efficient this way, since btree isn't all that happy 
+	 * with large numbers of equal keys.
 	 */
 
 	indexInfo = makeNode(IndexInfo);

src/test/regress/expected/strings.out

@@ -579,6 +579,13 @@ SELECT text 'text' || varchar ' and varchar' AS "Concat text to varchar";
 CREATE TABLE toasttest(f1 text);
 insert into toasttest values(repeat('1234567890',10000));
 insert into toasttest values(repeat('1234567890',10000));
+--
+-- Ensure that some values are uncompressed, to test the faster substring
+-- operation used in that case
+--
+alter table toasttest alter column f1 set storage external;
+insert into toasttest values(repeat('1234567890',10000));
+insert into toasttest values(repeat('1234567890',10000));
 -- If the starting position is zero or less, then return from the start of the string
 -- adjusting the length to be consistent with the "negative start" per SQL92.
 SELECT substr(f1, -1, 5) from toasttest;
@@ -586,7 +593,9 @@ SELECT substr(f1, -1, 5) from toasttest;
 --------
  123
  123
-(2 rows)
+ 123
+ 123
+(4 rows)
 
 -- If the length is less than zero, an ERROR is thrown.
 SELECT substr(f1, 5, -1) from toasttest;
@@ -598,7 +607,9 @@ SELECT substr(f1, 99995) from toasttest;
 --------
  567890
  567890
-(2 rows)
+ 567890
+ 567890
+(4 rows)
 
 -- If start plus length is > string length, the result is truncated to
 -- string length
@@ -607,7 +618,9 @@ SELECT substr(f1, 99995, 10) from toasttest;
 --------
  567890
  567890
-(2 rows)
+ 567890
+ 567890
+(4 rows)
 
 DROP TABLE toasttest;
 --
@@ -616,6 +629,13 @@ DROP TABLE toasttest;
 CREATE TABLE toasttest(f1 bytea);
 insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
 insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
+--
+-- Ensure that some values are uncompressed, to test the faster substring
+-- operation used in that case
+--
+alter table toasttest alter column f1 set storage external;
+insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
+insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
 -- If the starting position is zero or less, then return from the start of the string
 -- adjusting the length to be consistent with the "negative start" per SQL92.
 SELECT substr(f1, -1, 5) from toasttest;
@@ -623,7 +643,9 @@ SELECT substr(f1, -1, 5) from toasttest;
 --------
  123
  123
-(2 rows)
+ 123
+ 123
+(4 rows)
 
 -- If the length is less than zero, an ERROR is thrown.
 SELECT substr(f1, 5, -1) from toasttest;
@@ -635,7 +657,9 @@ SELECT substr(f1, 99995) from toasttest;
 --------
  567890
  567890
-(2 rows)
+ 567890
+ 567890
+(4 rows)
 
 -- If start plus length is > string length, the result is truncated to
 -- string length
@@ -644,7 +668,9 @@ SELECT substr(f1, 99995, 10) from toasttest;
 --------
  567890
  567890
-(2 rows)
+ 567890
+ 567890
+(4 rows)
 
 DROP TABLE toasttest;
 --

src/test/regress/sql/strings.sql

@@ -206,6 +206,14 @@ CREATE TABLE toasttest(f1 text);
 insert into toasttest values(repeat('1234567890',10000));
 insert into toasttest values(repeat('1234567890',10000));
 
+--
+-- Ensure that some values are uncompressed, to test the faster substring
+-- operation used in that case
+--
+alter table toasttest alter column f1 set storage external;
+insert into toasttest values(repeat('1234567890',10000));
+insert into toasttest values(repeat('1234567890',10000));
+
 -- If the starting position is zero or less, then return from the start of the string
 -- adjusting the length to be consistent with the "negative start" per SQL92.
 SELECT substr(f1, -1, 5) from toasttest;
@@ -231,6 +239,14 @@ CREATE TABLE toasttest(f1 bytea);
 insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
 insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
 
+--
+-- Ensure that some values are uncompressed, to test the faster substring
+-- operation used in that case
+--
+alter table toasttest alter column f1 set storage external;
+insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
+insert into toasttest values(decode(repeat('1234567890',10000),'escape'));
+
 -- If the starting position is zero or less, then return from the start of the string
 -- adjusting the length to be consistent with the "negative start" per SQL92.
 SELECT substr(f1, -1, 5) from toasttest;