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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:
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amatsuda committed Jan 27, 2016
1 parent 3844854 commit 42dd2336b31a8d98776d039a2b9fd7f834156a78
@@ -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
@@ -957,9 +957,9 @@ def foreign_key_options(from_table, to_table, options) # :nodoc:
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"
# Should not be called normally, but this operation is non-destructive.
@@ -987,14 +987,12 @@ def assume_migrated_upto_version(version, migrations_paths)
execute "INSERT INTO #{sm_table} (version) VALUES ('#{version}')"
inserted =
(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."
execute "INSERT INTO #{sm_table} (version) VALUES #{ {|v| '(#{v})'}.join(', ') }"

2 comments on commit 42dd233


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jeremy replied Apr 21, 2016

This has caused some issues for people on older SQLite.

It's a tough bug to diagnose because it isn't obvious that SQLite doesn't support multi-insert. The SQL certainly looks fine, but it complains there's an error!

Proposal to bump Rails 5 minimum SQLite version to 3.8+ in response:

Maybe it'd be simpler to do a multi-insert only if the adapter supports it? Then the adapter is free to version-check or feature-check the database to see whether it's possible.


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vipulnsward replied Apr 22, 2016

It makes sense to allow both given the number of bug reports we have had and that Ubuntu 12.04 LTS uses unsupported version. I will send a PR for this.

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