diff options
Diffstat (limited to 'src/backend/access/heap/tuptoaster.c')
| -rw-r--r-- | src/backend/access/heap/tuptoaster.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/src/backend/access/heap/tuptoaster.c b/src/backend/access/heap/tuptoaster.c index da878a73483..ae6a3fa0ec2 100644 --- a/src/backend/access/heap/tuptoaster.c +++ b/src/backend/access/heap/tuptoaster.c @@ -2406,8 +2406,21 @@ init_toast_snapshot(Snapshot toast_snapshot) { Snapshot snapshot = GetOldestSnapshot(); + /* + * GetOldestSnapshot returns NULL if the session has no active snapshots. + * We can get that if, for example, a procedure fetches a toasted value + * into a local variable, commits, and then tries to detoast the value. + * Such coding is unsafe, because once we commit there is nothing to + * prevent the toast data from being deleted. Detoasting *must* happen in + * the same transaction that originally fetched the toast pointer. Hence, + * rather than trying to band-aid over the problem, throw an error. (This + * is not very much protection, because in many scenarios the procedure + * would have already created a new transaction snapshot, preventing us + * from detecting the problem. But it's better than nothing, and for sure + * we shouldn't expend code on masking the problem more.) + */ if (snapshot == NULL) - elog(ERROR, "no known snapshots"); + elog(ERROR, "cannot fetch toast data without an active snapshot"); InitToastSnapshot(*toast_snapshot, snapshot->lsn, snapshot->whenTaken); } |