Django中的原始查询比Postgres中的原始查询慢得多

Question

I face the problem of an extremely slow (raw) query in my Django app. Strangely enough, it's not slow when I launch the isolated query from the shell (ex: python manage.py my_code_query) but it's slow when I run the whole program that contains all my querys (it "blocks" always at the same query; actually it eventually completes but it's something like 100x slower). It's like if all the queries that are before the problematic one are consuming memory and there is not enough memory left when my query starts. The query ran directly from Postgres has no problem at all.

I read somewhere ( Django cursor.execute(QUERY) much slower than running the query in the postgres database ) that it can be the work_mem setting in Postgres that causes the problem but they are not very clear about the way they set it from Django. Do I have to make a call from my connection.cursor.execute() to set the work_mem parameter? Once only?

Could it be another problem than the work_mem setting?

Any hint will be very appreciated. Thanks, Patrick

Answer 1

Inspired by that post ( How can I tell Django to execute all queries using 10MB statement mem? ), I made this call before executing my cursor:

cursor.execute("set work_mem='100MB'") #set statement_mem does not work

It's running timely now.

--EDIT: Well, that was yesterday. Today it's not running timely anymore. Don't know why.