diff options
| -rw-r--r-- | src/backend/access/transam/multixact.c | 23 |
1 files changed, 17 insertions, 6 deletions
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 68b0e101473..5e0bda7e700 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -2492,13 +2492,24 @@ DetermineSafeOldestOffset(MultiXactId oldestMXact) return; /* - * We determine the safe upper bound for offsets of new xacts by reading - * the offset of the oldest multixact, and going back one segment. This - * way, the sequence of multixact member segments will always have a - * one-segment hole at a minimum. We start spewing warnings a few - * complete segments before that. + * Determine the offset of the oldest multixact. Normally, we can read + * the offset from the multixact itself, but there's an important special + * case: if there are no multixacts in existence at all, oldestMXact + * obviously can't point to one. It will instead point to the multixact + * ID that will be assigned the next time one is needed. */ - oldestOffset = find_multixact_start(oldestMXact); + LWLockAcquire(MultiXactGenLock, LW_SHARED); + if (MultiXactState->nextMXact == oldestMXact) + { + oldestOffset = MultiXactState->nextOffset; + LWLockRelease(MultiXactGenLock); + } + else + { + LWLockRelease(MultiXactGenLock); + oldestOffset = find_multixact_start(oldestMXact); + } + /* move back to start of the corresponding segment */ oldestOffset -= oldestOffset % (MULTIXACT_MEMBERS_PER_PAGE * SLRU_PAGES_PER_SEGMENT); |