[Tom Lane <tgl@sss.pgh.pa.us>]

I wrote:
> Also, I fail to understand why fmgr_builtin_oid_index has 10000 entries
> anyway.  We could easily have fmgrtab.c expose the last actually assigned
> builtin function OID (presently 6121) and make the index array only
> that big, which just about eliminates the space advantage completely.

Concretely, like the attached.

We could make the index table still smaller if we wanted to reassign
a couple dozen high-numbered functions down to lower OIDs, but I dunno
if it's worth the trouble.  It certainly isn't from a performance
standpoint, because those unused entry ranges will never be touched
in normal usage; but it'd make the server executable a couple KB smaller.

			regards, tom lane

Attachments:

  [text/x-diff] make-fmgr-builtin-oid-index-smaller.patch (4.6K, ../12359.1547063064@sss.pgh.pa.us/2-make-fmgr-builtin-oid-index-smaller.patch)
  download | inline diff:
diff --git a/src/backend/utils/Gen_fmgrtab.pl b/src/backend/utils/Gen_fmgrtab.pl
index cafe408..f970940 100644
*** a/src/backend/utils/Gen_fmgrtab.pl
--- b/src/backend/utils/Gen_fmgrtab.pl
*************** foreach my $datfile (@input_files)
*** 80,90 ****
  	$catalog_data{$catname} = Catalog::ParseData($datfile, $schema, 0);
  }
  
- # Fetch some values for later.
- my $FirstGenbkiObjectId =
-   Catalog::FindDefinedSymbol('access/transam.h', $include_path,
- 	'FirstGenbkiObjectId');
- 
  # Collect certain fields from pg_proc.dat.
  my @fmgr = ();
  
--- 80,85 ----
*************** my %bmap;
*** 225,230 ****
--- 220,226 ----
  $bmap{'t'} = 'true';
  $bmap{'f'} = 'false';
  my @fmgr_builtin_oid_index;
+ my $last_builtin_oid = 0;
  my $fmgr_count = 0;
  foreach my $s (sort { $a->{oid} <=> $b->{oid} } @fmgr)
  {
*************** foreach my $s (sort { $a->{oid} <=> $b->
*** 232,237 ****
--- 228,234 ----
  	  "  { $s->{oid}, $s->{nargs}, $bmap{$s->{strict}}, $bmap{$s->{retset}}, \"$s->{prosrc}\", $s->{prosrc} }";
  
  	$fmgr_builtin_oid_index[ $s->{oid} ] = $fmgr_count++;
+ 	$last_builtin_oid = $s->{oid};
  
  	if ($fmgr_count <= $#fmgr)
  	{
*************** foreach my $s (sort { $a->{oid} <=> $b->
*** 244,274 ****
  }
  print $tfh "};\n";
  
! print $tfh qq|
  const int fmgr_nbuiltins = (sizeof(fmgr_builtins) / sizeof(FmgrBuiltin));
! |;
  
  
  # Create fmgr_builtins_oid_index table.
! #
! # Note that the array has to be filled up to FirstGenbkiObjectId,
! # as we can't rely on zero initialization as 0 is a valid mapping.
! print $tfh qq|
! const uint16 fmgr_builtin_oid_index[FirstGenbkiObjectId] = {
! |;
  
! for (my $i = 0; $i < $FirstGenbkiObjectId; $i++)
  {
  	my $oid = $fmgr_builtin_oid_index[$i];
  
! 	# fmgr_builtin_oid_index is sparse, map nonexistant functions to
  	# InvalidOidBuiltinMapping
  	if (not defined $oid)
  	{
  		$oid = 'InvalidOidBuiltinMapping';
  	}
  
! 	if ($i + 1 == $FirstGenbkiObjectId)
  	{
  		print $tfh "  $oid\n";
  	}
--- 241,270 ----
  }
  print $tfh "};\n";
  
! printf $tfh qq|
  const int fmgr_nbuiltins = (sizeof(fmgr_builtins) / sizeof(FmgrBuiltin));
! 
! const Oid fmgr_last_builtin_oid = %u;
! |, $last_builtin_oid;
  
  
  # Create fmgr_builtins_oid_index table.
! printf $tfh qq|
! const uint16 fmgr_builtin_oid_index[%u] = {
! |, $last_builtin_oid + 1;
  
! for (my $i = 0; $i <= $last_builtin_oid; $i++)
  {
  	my $oid = $fmgr_builtin_oid_index[$i];
  
! 	# fmgr_builtin_oid_index is sparse, map nonexistent functions to
  	# InvalidOidBuiltinMapping
  	if (not defined $oid)
  	{
  		$oid = 'InvalidOidBuiltinMapping';
  	}
  
! 	if ($i == $last_builtin_oid)
  	{
  		print $tfh "  $oid\n";
  	}
diff --git a/src/backend/utils/fmgr/fmgr.c b/src/backend/utils/fmgr/fmgr.c
index b41649f..506eeef 100644
*** a/src/backend/utils/fmgr/fmgr.c
--- b/src/backend/utils/fmgr/fmgr.c
*************** fmgr_isbuiltin(Oid id)
*** 75,86 ****
  	uint16		index;
  
  	/* fast lookup only possible if original oid still assigned */
! 	if (id >= FirstGenbkiObjectId)
  		return NULL;
  
  	/*
  	 * Lookup function data. If there's a miss in that range it's likely a
! 	 * nonexistant function, returning NULL here will trigger an ERROR later.
  	 */
  	index = fmgr_builtin_oid_index[id];
  	if (index == InvalidOidBuiltinMapping)
--- 75,86 ----
  	uint16		index;
  
  	/* fast lookup only possible if original oid still assigned */
! 	if (id > fmgr_last_builtin_oid)
  		return NULL;
  
  	/*
  	 * Lookup function data. If there's a miss in that range it's likely a
! 	 * nonexistent function, returning NULL here will trigger an ERROR later.
  	 */
  	index = fmgr_builtin_oid_index[id];
  	if (index == InvalidOidBuiltinMapping)
diff --git a/src/include/utils/fmgrtab.h b/src/include/utils/fmgrtab.h
index a778f88..e981f34 100644
*** a/src/include/utils/fmgrtab.h
--- b/src/include/utils/fmgrtab.h
*************** extern const FmgrBuiltin fmgr_builtins[]
*** 36,46 ****
  
  extern const int fmgr_nbuiltins;	/* number of entries in table */
  
  /*
!  * Mapping from a builtin function's oid to the index in the fmgr_builtins
!  * array.
   */
  #define InvalidOidBuiltinMapping PG_UINT16_MAX
! extern const uint16 fmgr_builtin_oid_index[FirstGenbkiObjectId];
  
  #endif							/* FMGRTAB_H */
--- 36,48 ----
  
  extern const int fmgr_nbuiltins;	/* number of entries in table */
  
+ extern const Oid fmgr_last_builtin_oid; /* highest function OID in table */
+ 
  /*
!  * Mapping from a builtin function's OID to its index in the fmgr_builtins
!  * array.  This is indexed from 0 through fmgr_last_builtin_oid.
   */
  #define InvalidOidBuiltinMapping PG_UINT16_MAX
! extern const uint16 fmgr_builtin_oid_index[];
  
  #endif							/* FMGRTAB_H */