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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

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,