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Introduce GUC_NO_RESET flag.

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Previously, the transaction-property GUCs such as transaction_isolation
could be reset after starting a transaction, because we marked them
as GUC_NO_RESET_ALL but still allowed a targeted RESET.  That leads to
assertion failures or worse, because those properties aren't supposed
to change after we've acquired a transaction snapshot.

There are some NO_RESET_ALL variables for which RESET is okay, so
we can't just redefine the semantics of that flag.  Instead introduce
a separate GUC_NO_RESET flag.  Mark "seed", as well as the transaction
property GUCs, as GUC_NO_RESET.

We have to disallow GUC_ACTION_SAVE as well as straight RESET, because
otherwise a function having a "SET transaction_isolation" clause can
still break things: the end-of-function restore action is equivalent
to a RESET.

No back-patch, as it's conceivable that someone is doing something
this patch will forbid (like resetting one of these GUCs at transaction
start, or "CREATE FUNCTION ... SET transaction_read_only = 1") and not
running into problems with it today.  Given how long we've had this
issue and not noticed, the side effects in non-assert builds can't be
too serious.

Per bug #17385 from Andrew Bille.

Masahiko Sawada

Discussion: https://postgr.es/m/17385-9ee529fb091f0ce5@postgresql.org
This commit is contained in:
Tom Lane
2022-09-27 11:47:12 -04:00
parent 4148c8b3da
commit 3853664265
11 changed files with 103 additions and 13 deletions
Download Patch File Download Diff File Expand all files Collapse all files

20
src/backend/utils/misc/guc.c
View File

@@ -3243,6 +3243,26 @@ set_config_option_ext(const char *name, const char *value,
}
}
/* Disallow resetting and saving GUC_NO_RESET values */
if (record->flags & GUC_NO_RESET)
{
if (value == NULL)
{
ereport(elevel,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("parameter \"%s\" cannot be reset", name)));
return 0;
}
if (action == GUC_ACTION_SAVE)
{
ereport(elevel,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("parameter \"%s\" cannot be set locally in functions",
name)));
return 0;
}
}
/*
* Should we set reset/stacked values? (If so, the behavior is not
* transactional.) This is done either when we get a default value from

7
src/backend/utils/misc/guc_funcs.c
View File

@@ -141,9 +141,6 @@ ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
WarnNoTransactionBlock(isTopLevel, "SET LOCAL");
/* fall through */
case VAR_RESET:
if (strcmp(stmt->name, "transaction_isolation") == 0)
WarnNoTransactionBlock(isTopLevel, "RESET TRANSACTION");
(void) set_config_option(stmt->name,
NULL,
(superuser() ? PGC_SUSET : PGC_USERSET),
@@ -539,7 +536,7 @@ ShowAllGUCConfig(DestReceiver *dest)
Datum
pg_settings_get_flags(PG_FUNCTION_ARGS)
{
#define MAX_GUC_FLAGS 5
#define MAX_GUC_FLAGS 6
char *varname = TextDatumGetCString(PG_GETARG_DATUM(0));
struct config_generic *record;
int cnt = 0;
@@ -554,6 +551,8 @@ pg_settings_get_flags(PG_FUNCTION_ARGS)
if (record->flags & GUC_EXPLAIN)
flags[cnt++] = CStringGetTextDatum("EXPLAIN");
if (record->flags & GUC_NO_RESET)
flags[cnt++] = CStringGetTextDatum("NO_RESET");
if (record->flags & GUC_NO_RESET_ALL)
flags[cnt++] = CStringGetTextDatum("NO_RESET_ALL");
if (record->flags & GUC_NO_SHOW_ALL)

8
src/backend/utils/misc/guc_tables.c
View File

@@ -1505,7 +1505,7 @@ struct config_bool ConfigureNamesBool[] =
{"transaction_read_only", PGC_USERSET, CLIENT_CONN_STATEMENT,
gettext_noop("Sets the current transaction's read-only status."),
NULL,
GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
},
&XactReadOnly,
false,
@@ -1524,7 +1524,7 @@ struct config_bool ConfigureNamesBool[] =
{"transaction_deferrable", PGC_USERSET, CLIENT_CONN_STATEMENT,
gettext_noop("Whether to defer a read-only serializable transaction until it can be executed with no possible serialization failures."),
NULL,
GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
},
&XactDeferrable,
false,
@@ -3606,7 +3606,7 @@ struct config_real ConfigureNamesReal[] =
{"seed", PGC_USERSET, UNGROUPED,
gettext_noop("Sets the seed for random-number generation."),
NULL,
GUC_NO_SHOW_ALL | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
GUC_NO_SHOW_ALL | GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
},
&phony_random_seed,
0.0, -1.0, 1.0,
@@ -4557,7 +4557,7 @@ struct config_enum ConfigureNamesEnum[] =
{"transaction_isolation", PGC_USERSET, CLIENT_CONN_STATEMENT,
gettext_noop("Sets the current transaction's isolation level."),
NULL,
GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
GUC_NO_RESET | GUC_NO_RESET_ALL | GUC_NOT_IN_SAMPLE | GUC_DISALLOW_IN_FILE
},
&XactIsoLevel,
XACT_READ_COMMITTED, isolation_level_options,