use strict;
use warnings;

use constant CACHESIZE => 2**24; ## Default size of cache memory (2**24=>16_777_216)
use constant PAGESIZE  => 2048;		

our %RCache = (); keys( %RCache ) = 1020;

$dbenv{DB_RMaxkeys} = CACHESIZE / PAGESIZE;
. . .
if ( scalar keys %RCache > $dbenv{DB_RMaxkeys} ) { &CheckMemoryUsage('WR'); }
. . .

if ( scalar keys %RCache > $dbenv{DB_RMaxkeys} ) { &CheckMemoryUsage('RN'); }
. . .

if ( scalar keys %RCache > $dbenv{DB_RMaxkeys} ) { &CheckMemoryUsage('RP'); }
. . .

# my $ret = &GetSubBuffer(\$db,$subtreeptr,\$buffer, $log )
sub GetSubBuffer
{	my ( $db, $ptr, $buffer, $log ) = @_; my $size = $dbenv{DB_InternalPageSize};
	if ( ( $CACHE == 1 )&&( exists $RCache{$ptr} ) )
	{	$$buffer = $RCache{$ptr}; }
	else
	{	if ( $ptr < $size ) { die "  GetSubBuffer: $log subtreeptr $ptr <= 0\n";  }
		$ret = sysseek( $$db{btree}, $ptr, 0);		# move to subtree location in file
		if ( ! defined $ret ) { die "  GetSubBuffer: $log sysseek failed:|$ptr| $!\n"; }
		$ret = sysread( $$db{btree},my $tmpbuf, $size );
		if ( $ret != $size ) { die "  GetSubBuffer: $log sysread failed: $!\n"; }
		my $reclen = unpack("N", substr($tmpbuf,0,4));

		if ( ! defined $$buffer ) { die "$log buffer not defined!"; }
		substr($$buffer,0,$reclen+4,$tmpbuf); #*#
		if ( $CACHE == 1 )
		{	$RCache{$ptr} = $$buffer; }
	}
}
sub CheckMemoryUsage
{	our %RCache;
	use Devel::Size qw(total_size);
	my $log = shift;
	my $stime = gettimeofday; my $keys = scalar keys %RCache;
	print $DLOG "MEM_CK-$log: Enter:  Keys:$keys   \%RCache Size: ",total_size(\%RCache),"\n";
	my ( $vmem, $rmem ) = &Display_Mem_Usage($$,$NAME,0);

	my $rkeys = scalar keys %RCache;