Updated FSM display for VACUUM VERBOSE

I have trouble understanding the current output of VACUUM VERBOSE when
it displays FSM information.

The current output is:

    INFO:  free space map: 49 relations, 17266 pages stored; 18768 total
    pages used
    DETAIL:  FSM size: 1000 relations + 18000 pages = 171 kB shared memory.
    NOTICE:  the number of page slots needed (18768) exceeds max_fsm_pages
    (18000)
    HINT:  Consider increasing the configuration parameter "max_fsm_relations"
    to a value over 18768.

The problem I have is that the relations part is mixed with the pages
part, and the numbers aren't easily comparable.  I have attached a patch
which makes the information easier to understand.  Here is one where the
FSM is large enough:

    INFO:  free space map: 48 relations with free space, maximum of 1000 relations trackable
    INFO:  35 pages stored, 768 pages used (with overhead)
    INFO:  768 pages required to store all freespace, maximum of 18000 pages allocatable (171 kB)

and one that is too small:

    INFO:  free space map: 49 relations with free space, maximum of 1000 relations trackable
    INFO:  17266 pages stored, 18000 pages used (with overhead)
    INFO:  18768 pages required to store all freespace, maximum of 18000 pages allocatable (171 kB)
    NOTICE:  the number of page slots needed (18768) exceeds max_fsm_pages (18000)
    HINT:  Consider increasing the configuration parameter "max_fsm_relations"
    to a value over 18768.

I find this output cleaner and easier to understand.  The "pages used"
value will match either the "required" or "maximum" value on the line
below.

--
  Bruce Momjian                        |  http://candle.pha.pa.us
  pgman@candle.pha.pa.us               |  (610) 359-1001
  +  If your life is a hard drive,     |  13 Roberts Road
  +  Christ can be your backup.        |  Newtown Square, Pennsylvania 19073
Index: src/backend/storage/freespace/freespace.c
===================================================================
RCS file: /cvsroot/pgsql/src/backend/storage/freespace/freespace.c,v
retrieving revision 1.39
diff -c -c -r1.39 freespace.c
*** src/backend/storage/freespace/freespace.c    14 Mar 2005 20:15:09 -0000    1.39
--- src/backend/storage/freespace/freespace.c    23 Apr 2005 04:03:09 -0000
***************
*** 691,696 ****
--- 691,697 ----
      int            storedPages = 0;
      int            numRels;
      double        sumRequests;
+     double        extraChunks = 0;
      double        needed;

      LWLockAcquire(FreeSpaceLock, LW_EXCLUSIVE);
***************
*** 698,704 ****
--- 699,713 ----
      for (fsmrel = FreeSpaceMap->firstRel;
           fsmrel != NULL;
           fsmrel = fsmrel->nextPhysical)
+     {
          storedPages += fsmrel->storedPages;
+         if (!fsmrel->isIndex)
+             /* round so a full page doesn't count twice */
+             extraChunks += (fsmrel->storedPages-1) / CHUNKPAGES;
+         else
+             extraChunks += (fsmrel->storedPages-1) / INDEXCHUNKPAGES;
+     }
+
      /* Copy other stats before dropping lock */
      numRels = FreeSpaceMap->numRels;
      sumRequests = FreeSpaceMap->sumRequests;
***************
*** 708,718 ****
      needed = (sumRequests + numRels) * CHUNKPAGES;

      ereport(elevel,
!             (errmsg("free space map: %d relations, %d pages stored; %.0f total pages used",
!                     numRels, storedPages, needed),
!              errdetail("FSM size: %d relations + %d pages = %.0f kB shared memory.",
!                        MaxFSMRelations, MaxFSMPages,
!                        (double) FreeSpaceShmemSize() / 1024.0)));

      CheckFreeSpaceMapStatistics(NOTICE, numRels, needed);
      /* Print to server logs too because is deals with a config variable. */
--- 717,733 ----
      needed = (sumRequests + numRels) * CHUNKPAGES;

      ereport(elevel,
!             (errmsg("free space map: %d relations with free space, maximum of %d relations trackable",
!                     numRels, MaxFSMRelations)));
!
!     ereport(elevel,
!             (errmsg("%d pages stored, %.0f pages used (with overhead)",
!                     storedPages, (extraChunks + numRels) * CHUNKPAGES)));
!
!     ereport(elevel,
!             (errmsg("%.0f pages required to store all freespace, maximum of %d pages allocatable (%.0f kB)",
!                     needed, MaxFSMPages,
!                    (double) FreeSpaceShmemSize() / 1024.0)));

      CheckFreeSpaceMapStatistics(NOTICE, numRels, needed);
      /* Print to server logs too because is deals with a config variable. */