doc: Correct description of values used in FSM for indexes

michaelpq · michaelpq · commit e5cf186277f9 · 2025-03-27T10:20:51.000+09:00
The implementation of FSM for indexes is simpler than heap, where 0 is used to track if a page is in-use and (BLCKSZ - 1) if a page is free. One comment in indexfsm.c and one description in the documentation of pg_freespacemap were incorrect about that. Author: Alex Friedman <alexf01@gmail.com> Discussion: https://postgr.es/m/71eef655-c192-453f-ac45-2772fec2cb04@gmail.com Backpatch-through: 13
diff --git a/doc/src/sgml/pgfreespacemap.sgml b/doc/src/sgml/pgfreespacemap.sgml
@@ -66,7 +66,7 @@
   <para>
    For indexes, what is tracked is entirely-unused pages, rather than free
    space within pages.  Therefore, the values are not meaningful, just
-   whether a page is full or empty.
+   whether a page is in-use or empty.
   </para>
 
   <note>
diff --git a/src/backend/storage/freespace/indexfsm.c b/src/backend/storage/freespace/indexfsm.c
@@ -16,7 +16,7 @@
  *	This is similar to the FSM used for heap, in freespace.c, but instead
  *	of tracking the amount of free space on pages, we only track whether
  *	pages are completely free or in-use. We use the same FSM implementation
- *	as for heaps, using BLCKSZ - 1 to denote used pages, and 0 for unused.
+ *	as for heaps, using 0 to denote used pages, and (BLCKSZ - 1) for unused.
  *
  *-------------------------------------------------------------------------
  */

Original file line number	Diff line number	Diff line change
`@@ -16,7 +16,7 @@`
`16`	`16`	`* This is similar to the FSM used for heap, in freespace.c, but instead`
`17`	`17`	`* of tracking the amount of free space on pages, we only track whether`
`18`	`18`	`* pages are completely free or in-use. We use the same FSM implementation`
`19`		`- * as for heaps, using BLCKSZ - 1 to denote used pages, and 0 for unused.`
	`19`	`+ * as for heaps, using 0 to denote used pages, and (BLCKSZ - 1) for unused.`
`20`	`20`	`*`
`21`	`21`	`*-------------------------------------------------------------------------`
`22`	`22`	`*/`