Rails 2.1 MySQL 6.0 schema_migrations index problem
Reported by Jon Smillie | July 1st, 2008 @ 04:53 AM | in 2.x
This is the error I get when I enter the command rake db:migrate:
rake aborted!
Mysql::Error: #42000Specified key was too long; max key length is 767
bytes: CREATE UNIQUE INDEX 'unique_schema_migrations' ON
'schema_migrations' <'version'>
The problem is that MySQL has a limit of 767 bytes on the length of
columns used for keys. In UTF8 a varchar(255) consumes 1080 bytes. The
fix is to have the indexing done on a the first part of the key, by
limiting the key to so (say) the first 100 characters, by:
CREATE UNIQUE INDEX `unique_schema_migrations`
ON `schema_migrations` (`version` (100) )
In ActiveRecord 2.1.0 the code which creates the index on the
schema_migrations table is in
connection_adapters/abstract/schema_statements.rb on line 317. This
calls the "add_index" method defined on line 255. The actual sql
statement used to create the index is on line 266. Change this to:
execute "CREATE #{index_type} INDEX #{quote_column_name(index_name)}
ON #{quote_table_name(table_name)} (#{quoted_column_names} (100) )"
ie: add the "(100)" after the column_name, and this will instruct MySQL
to only build the index on the first 100 characters of this column, well
under the 767 byte limit.
Comments and changes to this ticket
-
Joshua Peek October 5th, 2008 @ 03:13 PM
- → State changed from “new” to “stale”
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