|
26 | 26 | * subtransactions of our own main transaction and so there can't be any |
27 | 27 | * race condition. |
28 | 28 | * |
| 29 | + * Summary of visibility functions: |
| 30 | + * |
| 31 | + * HeapTupleSatisfiesMVCC() |
| 32 | + * visible to supplied snapshot, excludes current command |
| 33 | + * HeapTupleSatisfiesNow() |
| 34 | + * visible to instant snapshot, excludes current command |
| 35 | + * HeapTupleSatisfiesUpdate() |
| 36 | + * like HeapTupleSatisfiesNow(), but with user-supplied command |
| 37 | + * counter and more complex result |
| 38 | + * HeapTupleSatisfiesSelf() |
| 39 | + * visible to instant snapshot and current command |
| 40 | + * HeapTupleSatisfiesDirty() |
| 41 | + * like HeapTupleSatisfiesSelf(), but includes open transactions |
| 42 | + * HeapTupleSatisfiesVacuum() |
| 43 | + * visible to any running transaction, used by VACUUM |
| 44 | + * HeapTupleSatisfiesToast() |
| 45 | + * visible unless part of interrupted vacuum, used for TOAST |
| 46 | + * HeapTupleSatisfiesAny() |
| 47 | + * all tuples are visible |
29 | 48 | * |
30 | 49 | * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group |
31 | 50 | * Portions Copyright (c) 1994, Regents of the University of California |
32 | 51 | * |
33 | 52 | * IDENTIFICATION |
34 | | - * $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.111 2009/01/01 17:23:53 momjian Exp $ |
| 53 | + * $PostgreSQL: pgsql/src/backend/utils/time/tqual.c,v 1.112 2009/03/09 13:08:05 momjian Exp $ |
35 | 54 | * |
36 | 55 | *------------------------------------------------------------------------- |
37 | 56 | */ |
@@ -277,7 +296,7 @@ HeapTupleSatisfiesSelf(HeapTupleHeader tuple, Snapshot snapshot, Buffer buffer) |
277 | 296 | * |
278 | 297 | * Note we do _not_ include changes made by the current command. This |
279 | 298 | * solves the "Halloween problem" wherein an UPDATE might try to re-update |
280 | | - * its own output tuples. |
| 299 | + * its own output tuples, http://en.wikipedia.org/wiki/Halloween_Problem. |
281 | 300 | * |
282 | 301 | * Note: |
283 | 302 | *Assumes heap tuple is valid. |
|