Improve comment: add note that grotty special case in mdread() is

required by hash index implementation.

diff --git a/src/backend/storage/smgr/md.c b/src/backend/storage/smgr/md.c
index 25051a9799cabaf80fb79fe8a882a748b76f9fd0..f8f82048f342ed35dfcbaab8a70e922784e12642 100644 (file)
--- a/src/backend/storage/smgr/md.c
+++ b/src/backend/storage/smgr/md.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *       $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.92 2002/08/06 02:36:34 tgl Exp $
+ *       $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.93 2002/11/12 15:26:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -434,8 +434,12 @@ mdread(Relation reln, BlockNumber blocknum, char *buffer)
        if ((nbytes = FileRead(v->mdfd_vfd, buffer, BLCKSZ)) != BLCKSZ)
        {
                /*
-                * If we are at EOF, return zeroes without complaining. (XXX Is
-                * this still necessary/a good idea??)
+                * If we are at or past EOF, return zeroes without complaining.
+                * Also substitute zeroes if we found a partial block at EOF.
+                *
+                * XXX this is really ugly, bad design.  However the current
+                * implementation of hash indexes requires it, because hash index
+                * pages are initialized out-of-order.
                 */
                if (nbytes == 0 ||
                        (nbytes > 0 && mdnblocks(reln) == blocknum))