Add regression test for short varlenas saved in TOAST relations

toast_save_datum() has for a very long time some code able to handle
short varlenas (values up to 126 bytes reduced to a 1-byte header),
converting such varlenas to an external on-disk TOAST pointer with the
value saved uncompressed in the secondary TOAST relation.

There was zero coverage for this code path.  This commit adds a test
able to exercise it, relying on two external attributes, one with a low
toast_tuple_target, so as it is possible to trigger the threshold for
the insertion of short varlenas into the TOAST relation.

Author: Nikhil Kumar Veldanda <veldanda.nikhilkumar17@gmail.com>
Co-authored-by: Michael Paquier <michael@paquier.xyz>
Discussion: https://postgr.es/m/aJAl7-NvIk0kZByz@paquier.xyz

2 files changed, 54 insertions, 0 deletions

diff --git a/src/test/regress/expected/strings.out b/src/test/regress/expected/strings.out
index 1bfd33de3f3..ba302da51e7 100644
--- a/src/test/regress/expected/strings.out
+++ b/src/test/regress/expected/strings.out
@@ -2091,6 +2091,40 @@ SELECT c FROM toasttest;
 (1 row)
 
 DROP TABLE toasttest;
+-- test with short varlenas (up to 126 data bytes reduced to a 1-byte header)
+-- being toasted.
+CREATE TABLE toasttest (f1 text, f2 text);
+ALTER TABLE toasttest SET (toast_tuple_target = 128);
+ALTER TABLE toasttest ALTER COLUMN f1 SET STORAGE EXTERNAL;
+ALTER TABLE toasttest ALTER COLUMN f2 SET STORAGE EXTERNAL;
+-- Here, the first value is a varlena large enough to make it toasted and
+-- stored uncompressed.  The second value is a short varlena, toasted
+-- and stored uncompressed.
+INSERT INTO toasttest values(repeat('1234', 1000), repeat('5678', 30));
+SELECT reltoastrelid::regclass AS reltoastname FROM pg_class
+  WHERE oid = 'toasttest'::regclass \gset
+-- There should be two values inserted in the toast relation.
+SELECT count(*) FROM :reltoastname WHERE chunk_seq = 0;
+ count 
+-------
+     2
+(1 row)
+
+SELECT substr(f1, 5, 10) AS f1_data, substr(f2, 5, 10) AS f2_data
+  FROM toasttest;
+  f1_data   |  f2_data   
+------------+------------
+ 1234123412 | 5678567856
+(1 row)
+
+SELECT pg_column_compression(f1) AS f1_comp, pg_column_compression(f2) AS f2_comp
+  FROM toasttest;
+ f1_comp | f2_comp 
+---------+---------
+         | 
+(1 row)
+
+DROP TABLE toasttest;
 --
 -- test length
 --
diff --git a/src/test/regress/sql/strings.sql b/src/test/regress/sql/strings.sql
index 92c445c2439..b94004cc08c 100644
--- a/src/test/regress/sql/strings.sql
+++ b/src/test/regress/sql/strings.sql
@@ -650,6 +650,26 @@ SELECT length(c), c::text FROM toasttest;
 SELECT c FROM toasttest;
 DROP TABLE toasttest;
 
+-- test with short varlenas (up to 126 data bytes reduced to a 1-byte header)
+-- being toasted.
+CREATE TABLE toasttest (f1 text, f2 text);
+ALTER TABLE toasttest SET (toast_tuple_target = 128);
+ALTER TABLE toasttest ALTER COLUMN f1 SET STORAGE EXTERNAL;
+ALTER TABLE toasttest ALTER COLUMN f2 SET STORAGE EXTERNAL;
+-- Here, the first value is a varlena large enough to make it toasted and
+-- stored uncompressed.  The second value is a short varlena, toasted
+-- and stored uncompressed.
+INSERT INTO toasttest values(repeat('1234', 1000), repeat('5678', 30));
+SELECT reltoastrelid::regclass AS reltoastname FROM pg_class
+  WHERE oid = 'toasttest'::regclass \gset
+-- There should be two values inserted in the toast relation.
+SELECT count(*) FROM :reltoastname WHERE chunk_seq = 0;
+SELECT substr(f1, 5, 10) AS f1_data, substr(f2, 5, 10) AS f2_data
+  FROM toasttest;
+SELECT pg_column_compression(f1) AS f1_comp, pg_column_compression(f2) AS f2_comp
+  FROM toasttest;
+DROP TABLE toasttest;
+
 --
 -- test length
 --