diff options
Diffstat (limited to 'src/backend/access')
| -rw-r--r-- | src/backend/access/transam/slru.c | 8 | ||||
| -rw-r--r-- | src/backend/access/transam/subtrans.c | 4 |
2 files changed, 10 insertions, 2 deletions
diff --git a/src/backend/access/transam/slru.c b/src/backend/access/transam/slru.c index 61249f4a12d..275058036a2 100644 --- a/src/backend/access/transam/slru.c +++ b/src/backend/access/transam/slru.c @@ -1208,6 +1208,14 @@ SimpleLruFlush(SlruCtl ctl, bool allow_redirtied) /* * Remove all segments before the one holding the passed page number + * + * All SLRUs prevent concurrent calls to this function, either with an LWLock + * or by calling it only as part of a checkpoint. Mutual exclusion must begin + * before computing cutoffPage. Mutual exclusion must end after any limit + * update that would permit other backends to write fresh data into the + * segment immediately preceding the one containing cutoffPage. Otherwise, + * when the SLRU is quite full, SimpleLruTruncate() might delete that segment + * after it has accrued freshly-written data. */ void SimpleLruTruncate(SlruCtl ctl, int cutoffPage) diff --git a/src/backend/access/transam/subtrans.c b/src/backend/access/transam/subtrans.c index f33ae407a60..d9a31d3c8d2 100644 --- a/src/backend/access/transam/subtrans.c +++ b/src/backend/access/transam/subtrans.c @@ -349,8 +349,8 @@ ExtendSUBTRANS(TransactionId newestXact) /* * Remove all SUBTRANS segments before the one holding the passed transaction ID * - * This is normally called during checkpoint, with oldestXact being the - * oldest TransactionXmin of any running transaction. + * oldestXact is the oldest TransactionXmin of any running transaction. This + * is called only during checkpoint. */ void TruncateSUBTRANS(TransactionId oldestXact) |