AR and postgres performace issue
Reported by Daniel Podlejski | July 17th, 2008 @ 05:13 PM | in 2.x
Using of unquoted values in find(id) may cause long seq scan on huge tables.
For example:
cvalley_dev=# EXPLAIN SELECT * FROM messages WHERE (messages."id" = 111111);
QUERY PLAN
-------------------------------------------------------------------------------
Index Scan using messages_pkey on messages (cost=0.00..8.35 rows=1 width=51)
Index Cond: (id = 111111)
(2 rows)
It's OK, but:
cvalley_dev=# EXPLAIN SELECT * FROM messages WHERE (messages."id" = 111111111111111111111111);
QUERY PLAN
----------------------------------------------------------------
Seq Scan on messages (cost=0.00..23400.56 rows=4588 width=51)
Filter: ((id)::numeric = 111111111111111111111111::numeric)
(2 rows)
Postgres cast ID to numeric, so can't use integer index.
When table is really huge, this can kill our database server.
Solution on AR level is to use quoted values:
cvalley_dev=# EXPLAIN SELECT * FROM messages WHERE (messages."id" = '111111');
QUERY PLAN
-------------------------------------------------------------------------------
Index Scan using messages_pkey on messages (cost=0.00..8.35 rows=1 width=51)
Index Cond: (id = 111111)
(2 rows)
cvalley_dev=# EXPLAIN SELECT * FROM messages WHERE (messages."id" = '111111111111111111111111');
ERROR: value "111111111111111111111111" is out of range for type integer
Comments and changes to this ticket
-
Joshua Peek October 23rd, 2008 @ 04:32 PM
- → State changed from “new” to “invalid”
Please Login or create a free account to add a new comment.
You can update this ticket by sending an email to from your email client. (help)
Create your profile
Help contribute to this project by taking a few moments to create your personal profile. Create your profile »
Source available from github
The Git repository resides at http://github.com/rails
Check out the current development trunk (Edge Rails) with:
git clone git://github.com/rails/rails.git
Creating or reviewing a patch
See the contributor guide.
Creating a feature request
Please don't. If you want a new feature in Rails, you'll have to pull up your sleeves and get busy yourself. Or convince someone else to do it. See the contributor guide on how to get going. But posting them here is just going to lead to ticket root.
Creating a bug report
When creating a bug report, be sure to include as much relevant information as possible. Post the code sample that causes the problem. Preferably, alter the unit tests and show through either changed or added tests how the expected behavior is not occuring.
Security vulnerabilities should be reported via an email to security@rubyonrails.org, do not use trac for reporting security vulnerabilities. All content in trac is publicly available as soon as it is posted.
Then don't get your hopes up. Unless you have a "Code Red, Mission Critical, The World is Coming to an End" kinda bug, you're creating this ticket in the hope that others with the same problem will be able to collaborate with you on solving it. Do not expect that the ticket automatically will see any activity or that others will jump to fix it. Creating a ticket like this is mostly to help yourself start on the path of fixing the problem and for others to sign on to with a "I'm having this problem too".
Tarmo Tänav