Using libpq is slower than querying psql.exe, where is the delay?

Question

PostgreSQL

There is a simple table with a small amount of test data, 10 rows. The database is located on the local computer, host=localhot. I make a simple query like UPDATE table_session SET session = 0 WHERE item_id = 30064; Where item_id is a PRIMARY KEY but not tied to a row index. EXPLAIN ANALYZE gives Planning Time 0.480 ms and Execution Time: 0.269 ms, which is quite normal for my normal computer. Then I make the same request through libpq using PQexec () and get a delay of 10 ms, that is, an order of magnitude more. Did PREPARE and still the same result. Where to dig?