Added information regarding the schema_migrations table in Active Record Migrations guide.

1 files changed, 8 insertions, 2 deletions

diff --git a/guides/source/migrations.textile b/guides/source/migrations.textile
index 52dba76e68..909815d6d7 100644
--- a/guides/source/migrations.textile
+++ b/guides/source/migrations.textile
@@ -8,8 +8,14 @@ production machines next time you deploy.
 
 Active Record tracks which migrations have already been run so all you have to
 do is update your source and run +rake db:migrate+. Active Record will work out
-which migrations should be run. It will also update your +db/schema.rb+ file to
-match the structure of your database.
+which migrations should be run by checking the hidden +schema_mirgrations+ database 
+table, which is created automatically after the initial invocaton of +rake db:migrate+.
++schema_migrations+ contains a sole column named +versions+ that holds the time
+stamps that are preappended to generated Active Record migrations. Each time stamp
+contained in +schema_migrations+ indicate that the migration associated with the
+time stamp has previously been invoked, and does not need to be run on future 
++rake db:migrate+ invocations. Active Record will also update your +db/schema.rb+
+file to match the up-to-date structure of your database.
 
 Migrations also allow you to describe these transformations using Ruby. The
 great thing about this is that (like most of Active Record's functionality) it