diff options
Diffstat (limited to 'src/backend/access/heap/heapam.c')
| -rw-r--r-- | src/backend/access/heap/heapam.c | 41 |
1 files changed, 23 insertions, 18 deletions
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c index af5325ea632..c2d4395807f 100644 --- a/src/backend/access/heap/heapam.c +++ b/src/backend/access/heap/heapam.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.179 2004/10/15 22:39:42 tgl Exp $ + * $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.180 2004/10/26 16:05:02 tgl Exp $ * * * INTERFACE ROUTINES @@ -878,14 +878,16 @@ heap_getnext(HeapScanDesc scan, ScanDirection direction) * is set to the buffer holding the tuple and TRUE is returned. The caller * must unpin the buffer when done with the tuple. * - * If the tuple is not found, then tuple->t_data is set to NULL, *userbuf - * is set to InvalidBuffer, and FALSE is returned. + * If the tuple is not found (ie, item number references a deleted slot), + * then tuple->t_data is set to NULL and FALSE is returned. * - * If the tuple is found but fails the time qual check, then FALSE will be - * returned. When the caller specifies keep_buf = true, we retain the pin - * on the buffer and return it in *userbuf (so the caller can still access - * the tuple); when keep_buf = false, the pin is released and *userbuf is set - * to InvalidBuffer. + * If the tuple is found but fails the time qual check, then FALSE is returned + * but tuple->t_data is left pointing to the tuple. + * + * keep_buf determines what is done with the buffer in the FALSE-result cases. + * When the caller specifies keep_buf = true, we retain the pin on the buffer + * and return it in *userbuf (so the caller must eventually unpin it); when + * keep_buf = false, the pin is released and *userbuf is set to InvalidBuffer. * * It is somewhat inconsistent that we ereport() on invalid block number but * return false on invalid item number. This is historical. The only @@ -914,6 +916,8 @@ heap_fetch(Relation relation, * InvalidBuffer on entry, that buffer will be released before reading * the new page. This saves a separate ReleaseBuffer step and hence * one entry into the bufmgr when looping through multiple fetches. + * Also, if *userbuf is the same buffer that holds the target tuple, + * we avoid bufmgr manipulation altogether. */ bool heap_release_fetch(Relation relation, @@ -962,8 +966,13 @@ heap_release_fetch(Relation relation, if (!ItemIdIsUsed(lp)) { LockBuffer(buffer, BUFFER_LOCK_UNLOCK); - ReleaseBuffer(buffer); - *userbuf = InvalidBuffer; + if (keep_buf) + *userbuf = buffer; + else + { + ReleaseBuffer(buffer); + *userbuf = InvalidBuffer; + } tuple->t_datamcxt = NULL; tuple->t_data = NULL; return false; @@ -1007,17 +1016,13 @@ heap_release_fetch(Relation relation, /* Tuple failed time qual, but maybe caller wants to see it anyway. */ if (keep_buf) - { *userbuf = buffer; - - return false; + else + { + ReleaseBuffer(buffer); + *userbuf = InvalidBuffer; } - /* Okay to release pin on buffer. */ - ReleaseBuffer(buffer); - - *userbuf = InvalidBuffer; - return false; } |