Tweak indexscan and seqscan code to arrange that steps from one page to

the next are handled by ReleaseAndReadBuffer rather than separate
ReleaseBuffer and ReadBuffer calls.  This cuts the number of acquisitions
of the BufMgrLock by a factor of 2 (possibly more, if an indexscan happens
to pull successive rows from the same heap page).  Unfortunately this
doesn't seem enough to get us out of the recently discussed context-switch
storm problem, but it's surely worth doing anyway.

1 files changed, 3 insertions, 1 deletions

diff --git a/src/include/access/nbtree.h b/src/include/access/nbtree.h
index 8601b802fcf..bf64b70ebcf 100644
--- a/src/include/access/nbtree.h
+++ b/src/include/access/nbtree.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.76 2004/02/03 17:34:03 tgl Exp $
+ * $PostgreSQL: pgsql/src/include/access/nbtree.h,v 1.77 2004/04/21 18:24:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -446,6 +446,8 @@ extern void _bt_metapinit(Relation rel, bool markvalid);
 extern Buffer _bt_getroot(Relation rel, int access);
 extern Buffer _bt_gettrueroot(Relation rel);
 extern Buffer _bt_getbuf(Relation rel, BlockNumber blkno, int access);
+extern Buffer _bt_relandgetbuf(Relation rel, Buffer obuf,
+							   BlockNumber blkno, int access);
 extern void _bt_relbuf(Relation rel, Buffer buf);
 extern void _bt_wrtbuf(Relation rel, Buffer buf);
 extern void _bt_wrtnorelbuf(Relation rel, Buffer buf);