Description:
------------
Oid of PostgreSQL buildin types (those defined in src/include/catalog/pg_type.h) should be hardcoded for performance.

Reason:
Currently, PHP do a "SELECT oid,typename FROM pg_type" on the first time get_field_name() is called. Results are cached.

In most case, it is called for build-in types, which can use hardcoded value in pg_type.h. The pg_type query is needed only if it miss.

I have some (non-PHP) application that create/drop lots of tables dynamically, pg_type is very bloated and a simple select all take ~1 second. If you can cut it down, it will be a great performance gain for me.

---
The related code is at: https://github.com/php/php-src/blob/master/ext/pgsql/pgsql.c#L2389


	if ((field_type = zend_hash_find_ptr(list, str.s)) != NULL) {
		ret = estrdup((char *)field_type->ptr);
	} else { /* hash all oid's */
		int i, num_rows;
		int oid_offset,name_offset;
		char *tmp_oid, *end_ptr, *tmp_name;
		zend_resource new_oid_entry;

		if ((result = PQexec(pgsql, "select oid,typname from pg_type")) == NULL || PQresultStatus(result) != PGRES_TUPLES_OK) {
			if (result) {
				PQclear(result);
			}


Expected result:
----------------
The pg_type query is run only if I query on custom type.

Actual result:
--------------
The pg_type query is run always.