Is it normal that sqlite.fetchall() is so slow?

Question

I have an sql query that selects from two inner joined tables. The execution of the select statement takes about 50 seconds. However, the fetchall() takes 788 seconds and it

Answer 1

By default fetchall() is as slow as looping over fetchone() due to the arraysize of the Cursor object being set to 1.

To speed things up you can loop over fetchmany(), but to see a performance gain, you need to provide it with a size parameter bigger than 1, otherwise it'll fetch "many" by batches of arraysize, i.e. 1.

It is quite possible that you can get the performance gain simply by raising the value of arraysize, but I have no experience doing this, so you may want to experiment with that first by doing something like:

>>> import sqlite3
>>> conn = sqlite3.connect(":memory:")
>>> cu = conn.cursor()
>>> cu.arraysize
1
>>> cu.arraysize = 10
>>> cu.arraysize
10

More on the above here: http://docs.python.org/library/sqlite3.html#sqlite3.Cursor.fetchmany