Likes are always slow if you must do a suffix match ( "%something" ), as no index can handle that. But if you're doing a prefix match ( "something%" ) it won't be that bad.
And there's no "how big is big". You can have a slow app with a thousand rows and a hundred queries per second, and you can have a fast one with a million rows and a query per second. It all depends on what you're doing. Get a book on database optimization, all big databases have one, then you'll undertand what's fast and what's slow about your database. - Maurício Linhares http://alinhavado.wordpress.com/ (pt-br) | http://blog.codevader.com/ (en) On Fri, Mar 13, 2009 at 3:11 PM, Mike C <[email protected]> wrote: > > Thanks, that makes things clearer. But how big is big? I don't plan on > my app being hugely popular, but would thousands of entries be ok? Is > there an area where LIKE starts to be really slow? > > On Mar 13, 11:06 am, Charles Johnson <[email protected]> wrote: >> On Fri, Mar 13, 2009 at 12:42 PM, Mike C <[email protected]> wrote: >> >> > I've heard that using LIKE is very slow, but I see it being used a lot >> > in examples, blogs etc. Is it really that bad? Since Rails doesn't >> > directly support Fulltext search, this is the easiest way to get >> > searching done, right? Or are there any other easier ways? I'm using >> > acts_as_indexed right now, but it still doesn't do what LIKE does. >> >> The problem with the sql "LIKE" is that it can render the use of an >> index impossible. Imagine a search like: >> >> @users = User.find(:all, :conditions => "first_name like '%ILL%'") >> >> The database will have to find BILL, GILL, JILL, JILLIAN, etc. If you have a >> few hundred or a few thousand users that may not be such an issue. Millions >> of users makes this a different issue altogether. A full table scan is >> needed, and what will you do with all those rows? >> >> The point is this, when you are tempted to use LIKE be sure the data set >> searched and returned are small and that you try to other ways to constrain >> the search. >> >> Cheers-- >> >> Charles > > > --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Ruby on Rails: Talk" group. To post to this group, send email to [email protected] To unsubscribe from this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en -~----------~----~----~----~------~----~------~--~---
