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Add regression test for short varlenas saved in TOAST relations

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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
This commit is contained in:
Michael Paquier
2025-08-06 17:22:03 +09:00
parent 0b6aea0384
commit 225ebfe30a
2 changed files with 54 additions and 0 deletions
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34
src/test/regress/expected/strings.out
View File

@@ -2090,6 +2090,40 @@ SELECT c FROM toasttest;
x
(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

20
src/test/regress/sql/strings.sql
View File

@@ -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
--