Table "internet.trafic_20080901"
  Column   |            Type             |       Modifiers
-----------+-----------------------------+------------------------
 ip_from   | inet                        | not null
 port_from | character varying( 10 )       | not null
 ip_to     | inet                        | not null
 bytes     | bigint                      | not null
 t_t       | smallint                    | not null
 place     | smallint                    | not null
 tm        | timestamp without time zone | not null default now()
 client_id | integer                     | not null
Indexes:
    "trafic_20080901_client_idx" btree (client_id)

db3=>      explain select * from internet.trafic_20080901 order by client_id;
                                    QUERY PLAN
-----------------------------------------------------------------------------------
 Sort  (cost= 23744033 . 47 .. 23944644 . 35  rows= 80244352  width= 43 )
   Sort Key: client_id
   ->  Seq Scan on trafic_20080901  (cost= 0 . 00 .. 1552201 . 52  rows= 80244352  width= 43 )
( 3  rows)

explain select client_id from internet.trafic_20080901 order by client_id;
                                    QUERY PLAN
----------------------------------------------------------------------------------
 Sort  (cost= 15927262 . 97 .. 16127873 . 85  rows= 80244352  width= 4 )
   Sort Key: client_id
   ->  Seq Scan on trafic_20080901  (cost= 0 . 00 .. 1552201 . 52  rows= 80244352  width= 4 )
( 3  rows)

#!/usr/bin/php -q
<?
function getmem($pid){
  exec("ps -o rss -p ".$pid, $o);
  return $o[ 1 ];
}

$connect=pg_connect("host=127.0.0.1 user=test password=test dbname=g3");
$pgpid=pg_get_pid($connect);

echo "Before query\n";
echo "php Process mem: ".getmem(getmypid()),"kb\n";
echo "postgres process mem: ".getmem($pgpid)."kb\n";

$query=pg_query($connect,'select * from temp');

echo "\nAfter query\n";
echo "php Process mem: ".getmem(getmypid()),"kb\n";
echo "postgres process mem: ".getmem($pgpid)."kb\n";

pg_close($connect);
?>

Before query
php Process mem:  5020kb
postgres process mem:  2144kb

After query
php Process mem: 795356kb
postgres process mem:  3504kb

#!/usr/bin/php -q
<?
function getmem($pid){
  exec("ps -o rss -p ".$pid, $o);
  return $o[ 1 ];
}

$connect=pg_connect("host=127.0.0.1 user=test password=test dbname=g3");
$pgpid=pg_get_pid($connect);

echo "Before query\n";
echo "php Process mem: ".getmem(getmypid()),"kb\n";
echo "postgres process mem: ".getmem($pgpid)."kb\n";

pg_query($connect,'begin transaction');
pg_query($connect,'declare test cursor for select * from temp');
echo "\nAfter build cursor\n";
echo "php Process mem: ".getmem(getmypid()),"kb\n";
echo "postgres process mem: ".getmem($pgpid)."kb\n";

$query=pg_query($connect,'fetch 100000 from test');
while(pg_num_rows($query)> 0 ){
  echo "\nAfter query\n";
  echo "php Process mem: ".getmem(getmypid()),"kb\n";
  echo "postgres process mem: ".getmem($pgpid)."kb\n";
  unset($query);
  $query=pg_query($connect,'fetch 100000 from test');
}

pg_query($connect,'close test');
pg_query($connect,'commit');
pg_close($connect);
?>

Before query
php Process mem:  5028kb
postgres process mem:  2144kb

After build cursor
php Process mem:  5068kb
postgres process mem:  3008kb

After query
php Process mem: 30468kb
postgres process mem:  3464kb

....

After query
php Process mem: 30668kb
postgres process mem:  3464kb

After query
php Process mem: 30672kb
postgres process mem:  3464kb

After query
php Process mem:  9072kb
postgres process mem:  3976kb