cursor.fetchmany vs DECLARE BINARY CURSOR and FETCH

Question

I am not sure which is the most effective or the disadvantages/advantages of each approach or whether they are technically the same thing ?

That is

cursor.execute("DECLARE super_cursor BINARY CURSOR FOR SELECT names FROM myTable")

while True:
cursor.execute("FETCH 1000 FROM super_cursor")
rows = cursor.fetchall()

as expressed in the answer given by alecxe python postgres can I fetchall() 1 million rows?

In comparison to:

while True:
    results = cursor.fetchmany(1000)
    if not results:
        break
    for result in results:
        yield result

Should one use fetchmany as specified in psycopg2 or DECLARE BINARY.

I Have assumed that fetchmany and DECLARE BINARY both setup a temporary table on the database server side... The client side is an Apache server.

The website I am working with does calculations on user input to that of data in the database... Hence needs to load large amounts of data for pattern matching.

Thank you.

Answer 1

I have 1B records in my DB, DECLARE BINARY CURSOR solution can imediately iterate over the table whereas fetchmany has a very big delay to start working which I assume is because of preprocessing and loading data to the memory. So in my case BINARY CURSOR is more efficient.