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Diffstat (limited to 'src/backend/access/transam/xlog.c')
| -rw-r--r-- | src/backend/access/transam/xlog.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c index f7d4750fc0b..60c0b7ec3af 100644 --- a/src/backend/access/transam/xlog.c +++ b/src/backend/access/transam/xlog.c @@ -1495,6 +1495,17 @@ WaitXLogInsertionsToFinish(XLogRecPtr upto) * calling LWLockUpdateVar. But if it has to sleep, it will * advertise the insertion point with LWLockUpdateVar before * sleeping. + * + * In this loop we are only waiting for insertions that started + * before WaitXLogInsertionsToFinish was called. The lack of + * memory barriers in the loop means that we might see locks as + * "unused" that have since become used. This is fine because + * they only can be used for later insertions that we would not + * want to wait on anyway. Not taking a lock to acquire the + * current insertingAt value means that we might see older + * insertingAt values. This is also fine, because if we read a + * value too old, we will add ourselves to the wait queue, which + * contains atomic operations. */ if (LWLockWaitForVar(&WALInsertLocks[i].l.lock, &WALInsertLocks[i].l.insertingAt, |