When you want to look up a specific word in a 500-page paper tome, where do you look? That's the same idea as database indexes =)
On Thu, Jul 7, 2011 at 09:04, Walter Lee Davis <wa...@wdstudio.com> wrote: > > On Jul 7, 2011, at 7:28 AM, Rodrigo Ruiz wrote: > > What is add_index for? >> >> Someone told me it was to add indexes to the database, but I still dont >> know what indexes are... first I thought they where other columns of the >> table, but apparently not. >> > > Indexes are a feature of the relational database. One way they work is to > organize common query features (sort by date added, for example) in the > database's structure so that they can happen much more quickly than a simple > brute-force approach could do. Other types of indexes can enforce uniqueness > (only one copy of this e-mail address may be added ever) at a fundamental > level. > > Adding an index to a column can return dramatic speed improvements on > reads, at the expense of slightly longer write times. Like anything, it's a > trade-off. > > Like anything to do with the raw database design, you'll have to read up on > the specifics of your particular RDBMS to figure out which sort of index > structure makes the most sense for your application. If you have access to > someone who is a DBA, they can tell you lots of useful tricks that you might > use. > > But always, add an index (for speed) when you are tuning, not before. An > index for uniqueness you can add if it makes sense in your design. > > Walter > > > -- > 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 > rubyonrails-talk@googlegroups.**com<rubyonrails-talk@googlegroups.com> > . > To unsubscribe from this group, send email to > rubyonrails-talk+unsubscribe@**googlegroups.com<rubyonrails-talk%2bunsubscr...@googlegroups.com> > . > For more options, visit this group at http://groups.google.com/** > group/rubyonrails-talk?hl=en<http://groups.google.com/group/rubyonrails-talk?hl=en> > . > > -- 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 rubyonrails-talk@googlegroups.com. To unsubscribe from this group, send email to rubyonrails-talk+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rubyonrails-talk?hl=en.
