diff options
Diffstat (limited to 'src/include/storage/bufmgr.h')
| -rw-r--r-- | src/include/storage/bufmgr.h | 32 |
1 files changed, 31 insertions, 1 deletions
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h index b514b4696d1..38b602724e1 100644 --- a/src/include/storage/bufmgr.h +++ b/src/include/storage/bufmgr.h @@ -239,7 +239,7 @@ extern bool BgBufferSync(struct WritebackContext *wb_context); extern void AtProcExit_LocalBuffers(void); -extern void TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page); +extern void TestForOldSnapshot_impl(Snapshot snapshot, Relation relation); /* in freelist.c */ extern BufferAccessStrategy GetAccessStrategy(BufferAccessStrategyType btype); @@ -257,6 +257,36 @@ extern void FreeAccessStrategy(BufferAccessStrategy strategy); #ifndef FRONTEND +/* + * Check whether the given snapshot is too old to have safely read the given + * page from the given table. If so, throw a "snapshot too old" error. + * + * This test generally needs to be performed after every BufferGetPage() call + * that is executed as part of a scan. It is not needed for calls made for + * modifying the page (for example, to position to the right place to insert a + * new index tuple or for vacuuming). It may also be omitted where calls to + * lower-level functions will have already performed the test. + * + * Note that a NULL snapshot argument is allowed and causes a fast return + * without error; this is to support call sites which can be called from + * either scans or index modification areas. + * + * For best performance, keep the tests that are fastest and/or most likely to + * exclude a page from old snapshot testing near the front. + */ +static inline void +TestForOldSnapshot(Snapshot snapshot, Relation relation, Page page) +{ + Assert(relation != NULL); + + if (old_snapshot_threshold >= 0 + && (snapshot) != NULL + && (snapshot)->satisfies == HeapTupleSatisfiesMVCC + && !XLogRecPtrIsInvalid((snapshot)->lsn) + && PageGetLSN(page) > (snapshot)->lsn) + TestForOldSnapshot_impl(snapshot, relation); +} + #endif /* FRONTEND */ #endif /* BUFMGR_H */ |