Re: performance of delete

I'm curious how long manually running a single delete query with the appropriate where clause would take. Surely there's a way to do that through the Django ORM without having to drop into raw SQL?

That being said, there are limits to how long a given query can be, so the ORM would have to do some intelligent batching of your IN clause, so maybe it does make sense to leave that hairy logic out of the ORM :-)

-- 
Matt Long

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On Wednesday, April 24, 2013 at 18:31, Larry Martell wrote:

I changed it to delete one row at a time and it's taking 3 minutes.

On Wed, Apr 24, 2013 at 6:38 PM, Setiaman Lee <setiaman.lee@gmail.com> wrote:

Larry,

Avoid to use IN clause. I'd say to insert the events you want to delete into

the temp table. You can put the session id or user id in temp table to

differentiate set of data from other users. Then do the delete by joining

the temp table to the Event_Message_ldx table. your sql might look like

this:

delete event_message_ldx

from temp

where event_message_ldx.event_id = temp.event_id

and temp.userid = %s

above SQL can be executed in Django using RAW SQL. See the link below.

https://docs.djangoproject.com/en/dev/topics/db/sql/

Test the SQL in the MySQL workspace when it works then move the code to the

Django.

Rgrds,

Setiaman Lee

On Thu, Apr 25, 2013 at 8:12 AM, Larry Martell <larry.martell@gmail.com>

wrote:

I have a table that has 2.5 million rows and 9 columns that are all

int except for 2 varchar(255) - i.e. not that big of a table. I am

executing this statement:

Event_Message_Idx.objects.filter(event_id__in=event_ids).delete()

Where event_ids has around 1,500 items in it. There is an index on

event_id. This statement is taking 1 hour and 5 minutes to run. There

is nothing else hitting the database at that time, and the machine

it's running on is 97% idle and has plenty of free memory. This seems

extremely excessive to me. I would guess it's because of the in

clause. Perhaps this is more of a MySQL question when a django one,

but is there some better way to do a delete like this in django?

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