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

tglsfdc · tglsfdc · commit 6929a1e6ad62 · 2002-11-12T15:26:30.000Z
required by hash index implementation.
diff --git 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))

Original file line number	Diff line number	Diff line change
`@@ -8,7 +8,7 @@`
`8`	`8`	`*`
`9`	`9`	`*`
`10`	`10`	`* IDENTIFICATION`
`11`		`- * $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.92 2002/08/06 02:36:34 tgl Exp $`
	`11`	`+ * $Header: /cvsroot/pgsql/src/backend/storage/smgr/md.c,v 1.93 2002/11/12 15:26:30 tgl Exp $`
`12`	`12`	`*`
`13`	`13`	`*-------------------------------------------------------------------------`
`14`	`14`	`*/`
`@@ -434,8 +434,12 @@ mdread(Relation reln, BlockNumber blocknum, char *buffer)`
`434`	`434`	`if ((nbytes = FileRead(v->mdfd_vfd, buffer, BLCKSZ)) != BLCKSZ)`
`435`	`435`	`{`
`436`	`436`	`/*`
`437`		`- * If we are at EOF, return zeroes without complaining. (XXX Is`
`438`		`- * this still necessary/a good idea??)`
	`437`	`+ * If we are at or past EOF, return zeroes without complaining.`
	`438`	`+ * Also substitute zeroes if we found a partial block at EOF.`
	`439`	`+ *`
	`440`	`+ * XXX this is really ugly, bad design. However the current`
	`441`	`+ * implementation of hash indexes requires it, because hash index`
	`442`	`+ * pages are initialized out-of-order.`
`439`	`443`	`*/`
`440`	`444`	`if (nbytes == 0 \|\|`
`441`	`445`	`(nbytes > 0 && mdnblocks(reln) == blocknum))`