INSERT INTO schema_migrations in 1 SQL

We found that inserting all 600 schema_migrations for our mid-sized app takes about a minute on a cloud based CI environment.

I assume that the original code did not use multi-row-insert because SQLite3 was not supporting the syntax back then,
but it's been supported since 3.7.11: http://www.sqlite.org/releaselog/3_7_11.html

2 files changed, 13 insertions, 10 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f3dc26ddb3..b59c9b4635 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,8 @@
+*   Improve schema_migrations insertion performance by inserting all versions
+    in one INSERT SQL.
+
+    *Akira Matsuda*, *Naoto Koshikawa*
+
 *   Using `references` or `belongs_to` in migrations will always add index
     for the referenced column by default, without adding `index: true` option
     to generated migration file. Users can opt out of this by passing
diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index 70868ebd03..002f2ea8ce 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -957,9 +957,9 @@ module ActiveRecord
       def dump_schema_information #:nodoc:
         sm_table = ActiveRecord::Migrator.schema_migrations_table_name
 
-        ActiveRecord::SchemaMigration.order('version').map { |sm|
-          "INSERT INTO #{sm_table} (version) VALUES ('#{sm.version}');"
-        }.join "\n\n"
+        sql = "INSERT INTO #{sm_table} (version) VALUES "
+        sql << ActiveRecord::SchemaMigration.order('version').pluck(:version).map {|v| "('#{v}')" }.join(', ')
+        sql << ";\n\n"
       end
 
       # Should not be called normally, but this operation is non-destructive.
@@ -987,14 +987,12 @@ module ActiveRecord
           execute "INSERT INTO #{sm_table} (version) VALUES ('#{version}')"
         end
 
-        inserted = Set.new
-        (versions - migrated).each do |v|
-          if inserted.include?(v)
-            raise "Duplicate migration #{v}. Please renumber your migrations to resolve the conflict."
-          elsif v < version
-            execute "INSERT INTO #{sm_table} (version) VALUES ('#{v}')"
-            inserted << v
+        inserting = (versions - migrated).select {|v| v < version}
+        if inserting.any?
+          if (duplicate = inserting.detect {|v| inserting.count(v) > 1})
+            raise "Duplicate migration #{duplicate}. Please renumber your migrations to resolve the conflict."
           end
+          execute "INSERT INTO #{sm_table} (version) VALUES #{inserting.map {|v| '(#{v})'}.join(', ') }"
         end
       end