Description:
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Our database has around 25K tables. Whenever a PHP script does a first call to pg_field_type(), it consumes a lot of CPU, memory and network traffic.
This is reproducible with all PHP versions from 5 to 7.2

The problem was narrowed down to the following query performed from ext/pgsql/pgsql.c get_field_name():

select oid,typname from pg_type

As postgresql defines several types for each table in the database, the above query produces over 76K rows on our system. All of those are put into a hashmap by get_field_name().

Obviously, rowset types present in pg_type table cannot be used as field types, and have to be excluded from the query.