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Commit7b90469

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Allow adding values to an enum type created in the current transaction.
Normally it is unsafe to allow ALTER TYPE ADD VALUE in a transaction block,because instances of the value could be added to indexes later in the sametransaction, and then they would still be accessible even if thetransaction rolls back. However, we can allow this if the enum type itselfwas created in the current transaction, because then any such indexes wouldhave to go away entirely on rollback.The reason for allowing this is to support pg_upgrade's new usage ofpg_restore --single-transaction: in --binary-upgrade mode, pg_dump emitsenum types as a succession of ALTER TYPE ADD VALUE commands so that it canpreserve the values' OIDs. The support is a bit limited, so we'll leaveit undocumented.Andres Freund
1 parent452739d commit7b90469

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5 files changed

+74
-11
lines changed

5 files changed

+74
-11
lines changed

‎src/backend/commands/typecmds.c

Lines changed: 21 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1169,7 +1169,7 @@ DefineEnum(CreateEnumStmt *stmt)
11691169
*Adds a new label to an existing enum.
11701170
*/
11711171
void
1172-
AlterEnum(AlterEnumStmt*stmt)
1172+
AlterEnum(AlterEnumStmt*stmt,boolisTopLevel)
11731173
{
11741174
Oidenum_type_oid;
11751175
TypeName*typename;
@@ -1183,12 +1183,31 @@ AlterEnum(AlterEnumStmt *stmt)
11831183
if (!HeapTupleIsValid(tup))
11841184
elog(ERROR,"cache lookup failed for type %u",enum_type_oid);
11851185

1186+
/*
1187+
* Ordinarily we disallow adding values within transaction blocks, because
1188+
* we can't cope with enum OID values getting into indexes and then having
1189+
* their defining pg_enum entries go away. However, it's okay if the enum
1190+
* type was created in the current transaction, since then there can be
1191+
* no such indexes that wouldn't themselves go away on rollback. (We
1192+
* support this case because pg_dump --binary-upgrade needs it.) We test
1193+
* this by seeing if the pg_type row has xmin == current XID and is not
1194+
* HEAP_UPDATED. If it is HEAP_UPDATED, we can't be sure whether the
1195+
* type was created or only modified in this xact. So we are disallowing
1196+
* some cases that could theoretically be safe; but fortunately pg_dump
1197+
* only needs the simplest case.
1198+
*/
1199+
if (HeapTupleHeaderGetXmin(tup->t_data)==GetCurrentTransactionId()&&
1200+
!(tup->t_data->t_infomask&HEAP_UPDATED))
1201+
/* safe to do inside transaction block */ ;
1202+
else
1203+
PreventTransactionChain(isTopLevel,"ALTER TYPE ... ADD");
1204+
11861205
/* Check it's an enum and check user has permission to ALTER the enum */
11871206
checkEnumOwner(tup);
11881207

11891208
/* Add the new label */
11901209
AddEnumLabel(enum_type_oid,stmt->newVal,
1191-
stmt->newValNeighbor,stmt->newValIsAfter,
1210+
stmt->newValNeighbor,stmt->newValIsAfter,
11921211
stmt->skipIfExists);
11931212

11941213
ReleaseSysCache(tup);

‎src/backend/tcop/utility.c

Lines changed: 1 addition & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -972,14 +972,7 @@ standard_ProcessUtility(Node *parsetree,
972972
caseT_AlterEnumStmt:/* ALTER TYPE (enum) */
973973
if (isCompleteQuery)
974974
EventTriggerDDLCommandStart(parsetree);
975-
976-
/*
977-
* We disallow this in transaction blocks, because we can't cope
978-
* with enum OID values getting into indexes and then having their
979-
* defining pg_enum entries go away.
980-
*/
981-
PreventTransactionChain(isTopLevel,"ALTER TYPE ... ADD");
982-
AlterEnum((AlterEnumStmt*)parsetree);
975+
AlterEnum((AlterEnumStmt*)parsetree,isTopLevel);
983976
break;
984977

985978
caseT_ViewStmt:/* CREATE VIEW */

‎src/include/commands/typecmds.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -26,7 +26,7 @@ extern void RemoveTypeById(Oid typeOid);
2626
externvoidDefineDomain(CreateDomainStmt*stmt);
2727
externvoidDefineEnum(CreateEnumStmt*stmt);
2828
externvoidDefineRange(CreateRangeStmt*stmt);
29-
externvoidAlterEnum(AlterEnumStmt*stmt);
29+
externvoidAlterEnum(AlterEnumStmt*stmt,boolisTopLevel);
3030
externOidDefineCompositeType(RangeVar*typevar,List*coldeflist);
3131
externOidAssignTypeArrayOid(void);
3232

‎src/test/regress/expected/enum.out

Lines changed: 24 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -556,6 +556,30 @@ ERROR: foreign key constraint "enumtest_bogus_child_parent_fkey" cannot be impl
556556
DETAIL: Key columns "parent" and "id" are of incompatible types: bogus and rainbow.
557557
DROP TYPE bogus;
558558
--
559+
-- check transactional behaviour of ALTER TYPE ... ADD VALUE
560+
--
561+
CREATE TYPE bogus AS ENUM('good');
562+
-- check that we can't add new values to existing enums in a transaction
563+
BEGIN;
564+
ALTER TYPE bogus ADD VALUE 'bad';
565+
ERROR: ALTER TYPE ... ADD cannot run inside a transaction block
566+
COMMIT;
567+
-- check that we recognize the case where the enum already existed but was
568+
-- modified in the current txn
569+
BEGIN;
570+
ALTER TYPE bogus RENAME TO bogon;
571+
ALTER TYPE bogon ADD VALUE 'bad';
572+
ERROR: ALTER TYPE ... ADD cannot run inside a transaction block
573+
ROLLBACK;
574+
DROP TYPE bogus;
575+
-- check that we *can* add new values to existing enums in a transaction,
576+
-- if the type is new as well
577+
BEGIN;
578+
CREATE TYPE bogus AS ENUM();
579+
ALTER TYPE bogus ADD VALUE 'good';
580+
ALTER TYPE bogus ADD VALUE 'ugly';
581+
ROLLBACK;
582+
--
559583
-- Cleanup
560584
--
561585
DROP TABLE enumtest_child;

‎src/test/regress/sql/enum.sql

Lines changed: 27 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -257,6 +257,33 @@ CREATE TYPE bogus AS ENUM('good', 'bad', 'ugly');
257257
CREATETABLEenumtest_bogus_child(parent bogusREFERENCES enumtest_parent);
258258
DROPTYPE bogus;
259259

260+
--
261+
-- check transactional behaviour of ALTER TYPE ... ADD VALUE
262+
--
263+
CREATETYPEbogusAS ENUM('good');
264+
265+
-- check that we can't add new values to existing enums in a transaction
266+
BEGIN;
267+
ALTERTYPE bogus ADD VALUE'bad';
268+
COMMIT;
269+
270+
-- check that we recognize the case where the enum already existed but was
271+
-- modified in the current txn
272+
BEGIN;
273+
ALTERTYPE bogus RENAME TO bogon;
274+
ALTERTYPE bogon ADD VALUE'bad';
275+
ROLLBACK;
276+
277+
DROPTYPE bogus;
278+
279+
-- check that we *can* add new values to existing enums in a transaction,
280+
-- if the type is new as well
281+
BEGIN;
282+
CREATETYPEbogusAS ENUM();
283+
ALTERTYPE bogus ADD VALUE'good';
284+
ALTERTYPE bogus ADD VALUE'ugly';
285+
ROLLBACK;
286+
260287
--
261288
-- Cleanup
262289
--

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