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Relax transactional restrictions on ALTER TYPE ... ADD VALUE.

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To prevent possibly breaking indexes on enum columns, we must keep
uncommitted enum values from getting stored in tables, unless we
can be sure that any such column is new in the current transaction.

Formerly, we enforced this by disallowing ALTER TYPE ... ADD VALUE
from being executed at all in a transaction block, unless the target
enum type had been created in the current transaction.  This patch
removes that restriction, and instead insists that an uncommitted enum
value can't be referenced unless it belongs to an enum type created
in the same transaction as the value.  Per discussion, this should be
a bit less onerous.  It does require each function that could possibly
return a new enum value to SQL operations to check this restriction,
but there aren't so many of those that this seems unmaintainable.

Andrew Dunstan and Tom Lane

Discussion: <4075.1459088427@sss.pgh.pa.us>
This commit is contained in:
Tom Lane
2016-09-05 12:59:55 -04:00
parent 016abf1fb8
commit 15bc038f9b
8 changed files with 191 additions and 40 deletions
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30
src/test/regress/sql/enum.sql
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@@ -262,26 +262,42 @@ DROP TYPE bogus;
--
CREATE TYPE bogus AS ENUM('good');
-- check that we can't add new values to existing enums in a transaction
-- check that we can add new values to existing enums in a transaction
-- but we can't use them
BEGIN;
ALTER TYPE bogus ADD VALUE 'bad';
ALTER TYPE bogus ADD VALUE 'new';
SAVEPOINT x;
SELECT 'new'::bogus; -- unsafe
ROLLBACK TO x;
SELECT enum_first(null::bogus); -- safe
SELECT enum_last(null::bogus); -- unsafe
ROLLBACK TO x;
SELECT enum_range(null::bogus); -- unsafe
ROLLBACK TO x;
COMMIT;
SELECT 'new'::bogus; -- now safe
SELECT enumlabel, enumsortorder
FROM pg_enum
WHERE enumtypid = 'bogus'::regtype
ORDER BY 2;
-- check that we recognize the case where the enum already existed but was
-- modified in the current txn
-- modified in the current txn; this should not be considered safe
BEGIN;
ALTER TYPE bogus RENAME TO bogon;
ALTER TYPE bogon ADD VALUE 'bad';
SELECT 'bad'::bogon;
ROLLBACK;
DROP TYPE bogus;
-- check that we *can* add new values to existing enums in a transaction,
-- if the type is new as well
-- check that we can add new values to existing enums in a transaction
-- and use them, if the type is new as well
BEGIN;
CREATE TYPE bogus AS ENUM();
ALTER TYPE bogus ADD VALUE 'good';
CREATE TYPE bogus AS ENUM('good');
ALTER TYPE bogus ADD VALUE 'bad';
ALTER TYPE bogus ADD VALUE 'ugly';
SELECT enum_range(null::bogus);
ROLLBACK;
--