pq_query error on update - php

Question

I'm new to postresql and i am ashamed to recognize that i am not sure how tot execute correctly an update .
Every time I am trying to pg_query($update); it gives me this : Query failed: ERROR: cannot execute UPDATE in a read-only transaction .
Before this update I have executed a select query .
The select statement retrieves 50000 rows from the database. To be even more specific I am trying to execute a when /case update on 1000 rows. The query is well-formed I have tested it .
$sqlstr = "update abcd set country = CASE" ;
$temp = "";
while($myrow = pg_fetch_assoc($result)) {
if ($cnt < 1000) {
$country = exec('geoiplookup '.$myrow['ip']);
$temp .= " WHEN id = ".$myrow['id']." then '".$country."'";
$cnt++;
}
else {
$sqlstr = $sqlstr.$temp." END ; ";
pg_query($sqlstr);
$temp = "";
}
}

Answer 1

$sqlstr = "update abcd set country = CASE" ;
$temp = "";
while($myrow = pg_fetch_assoc($result))
{
if ($cnt < 1000)
{
$country = exec('geoiplookup '.$myrow['ip']);
$temp .= " WHEN id = ".$myrow['id']." then '".$country."'";
$cnt++;
}
else
{
$sqlstr = $sqlstr.$temp." END ; ";
pg_query($sqlstr);
$temp = "";
}
}