huge performance issue with ActiveRecord::Base exists?

rubyonrails-talk
1

I was just running a relative simple exists? query:

Page.exists?(["id > ?",i])

which equates to

  SELECT COUNT(*) FROM `pages` WHERE (id > 1400000) LIMIT 1

You would think with a COUNT and a LIMIT 1, that things would be really fast, but its SUPER slow, its trying to count all the records greater than 1400000.

This is N times faster:

  SELECT * FROM `pages` WHERE (id > 1400000) LIMIT 1

Do you guys think this needs to be changed, or not worth changing COUNT(*) to just * even though its a "LIMIT 1" ?

2

COMPLETELY IGNORE this "issue", this was caused by an old overwrite of the exists? function that I had from years ago.

MY BAD!

3

I was just running a relative simple exists? query:

Page.exists?(["id > ?",i])

which equates to

SELECT COUNT(*) FROM `pages` WHERE (id > 1400000) LIMIT 1

You would think with a COUNT and a LIMIT 1, that things would be really fast, but its SUPER slow, its trying to count all the records greater than 1400000.

This is N times faster:

SELECT * FROM `pages` WHERE (id > 1400000) LIMIT 1

Do you guys think this needs to be changed, or not worth changing COUNT(*) to just * even though its a "LIMIT 1" ?

Which version of rails are you running? I've looked at the source of edge, 2-1-stable and 2-0-stable and for all those versions exists does not appear to use count. Are you sure the query is coming from there?

Fred

4

Fred, this was my mistake read, the post above yours.