Migrations Without a Restart on Heroku

I ran into a situation today where I had 10 long running background processes that were getting bogged down because we were missing an index. The app is running on Heroku on a shared database, so I don’t have the luxury of using psql to add the needed index. However, I wanted to figure out a way to add the index without restarting the long-running processes.

My solution was to log in via the console, and create the migration by hand.

heroku run console --app <your app name> irb(main):002:0* class AddIndexToSearches < ActiveRecord::Migration irb(main):003:1> def change irb(main):004:2> add_index :searches, :search_string, :quiet => true irb(main):005:2> end irb(main):006:1> end => nil irb(main):007:0> t = AddIndexToSearches.new => #<AddIndexToSearches:0x00000006a240a8 @name="AddIndexToSearches", @version=nil, @connection=nil> irb(main):008:0> t.change -- add_index(:searches, :search_string) (91.8ms) SELECT distinct i.relname, d.indisunique, d.indkey, t.oid FROM pg_class t INNER JOIN pg_index d ON t.oid = d.indrelid INNER JOIN pg_class i ON d.indexrelid = i.oid WHERE i.relkind = 'i' AND d.indisprimary = 'f' AND t.relname = 'searches' AND i.relnamespace IN (SELECT oid FROM pg_namespace WHERE nspname = ANY (current_schemas(false)) ) ORDER BY i.relname (207509.6ms) CREATE INDEX "index_searches_on_search_string" ON "searches" ("search_string") -> 207.6028s => #<PGresult:0x00000006c81328> irb(main):009:0> irb(main):010:0*

Once complete, I added a new migration within the source code that has the option :quiet => true (_updated: see note below), so that all environments/developers get the manually created index that resides in production. Had I just done a git push to heroku, the background processes would have restarted. The results of adding the needed index can be seen in our New Relic stats below:

[New Relic Stats [New Relic Stats After Index Added]]

Note: I thought :quiet was a valid option for add_index, but it is actually a patch that you will need to add for your specific database. The following article describes a patch for MySQL. See mine for PostGreSQL.

module ActiveRecord::ConnectionAdapters::SchemaStatements def add_index_with_quiet(table_name, column_names, options = {}) quiet = options.delete(:quiet) add_index_without_quiet table_name, column_names, options rescue raise unless quiet and $!.message =~ /^Index name '.*' on table '#{table_name}' already exists/i puts "Failed to create index #{table_name} #{column_names.inspect} #{options.inspect}" end alias_method_chain :add_index, :quiet end

Migrations Without a Restart on Heroku

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