in favor of `begin_transaction`
with `:joinable` option.

removed two instances of add_column_options! from abstract_mysql_adapter

reworked rename_column_sql to remove add_column_options from schema_statements

changed to use new hash syntax.

added comments to test_invalid_type in sqlite3 adapter test and added valid_type? method to abstract_adapter.rb and removed unnecessary method from sqlite3 adapter

Adds support for algorithm option in MySQL indexes
Moves USING and algorithm options upstream

The syntax is still specific to the Adapter, so the actual executed string happens
in the corresponding adapter

We should only type cast when we need to use.

Related to 4b005fb3

This revision makes the terminology uniform with the rest of the file.
In general we describe these methods in terms of the adapter, rather
than the database. (As a side note, if we wanted to refer to the
database we would write "PostgreSQL".)

It was supposed to be removed by the preceding two reversions but I did
them in the wrong order.

This reverts commit 5d528f83.

Relates to f8c8ad56 which is also getting reverted due to failing test.

[ci skip]

add ActiveRecord::AbstractAdapter#extensions and ActiveRecord::ConnectionAdapters::PostgreSQLAdapter#extensions to allow dumping of enabled extensions to schema.rb, add ActiveRecord::SchemaDumper#extensions to dump extensions to schema.rb

* dependencies/autoload
* concern
* deprecation

It's sometimes hard to quickly find where deprecated call was performed, especially in case of migrating between Rails versions. So this is an attempt to improve the call stack part of the warning message by providing caller explicitly.

If your database supports setting the isolation level for a transaction,
you can set it like so:

  Post.transaction(isolation: :serializable) do
    # ...
  end

Valid isolation levels are:

* `:read_uncommitted`
* `:read_committed`
* `:repeatable_read`
* `:serializable`

You should consult the documentation for your database to understand the
semantics of these different levels:

* http://www.postgresql.org/docs/9.1/static/transaction-iso.html
* https://dev.mysql.com/doc/refman/5.0/en/set-transaction.html

An `ActiveRecord::TransactionIsolationError` will be raised if:

* The adapter does not support setting the isolation level
* You are joining an existing open transaction
* You are creating a nested (savepoint) transaction

The mysql, mysql2 and postgresql adapters support setting the
transaction isolation level. However, support is disabled for mysql
versions below 5, because they are affected by a bug
(http://bugs.mysql.com/bug.php?id=39170) which means the isolation level
gets persisted outside the transaction.

This avoids us having to manually increment and decrement it.

This reverts commit c24c8852.

Here's the explanation I just sent to @tenderlove:

Hey,

I've been thinking about about the transaction memory leak thing that we
were discussing.

Example code:

post = nil
Post.transaction do
  N.times { post = Post.create }
end

Post.transaction is going to create a real transaction and there will
also be a (savepoint) transaction inside each Post.create.

In an idea world, we'd like all but the last Post instance to be GC'd,
and for the last Post instance to receive its after_commit callback when
Post.transaction returns.

I can't see how this can work using your solution where the Post itself
holds a reference to the transaction it is in; when Post.transaction
returns, control does not switch to any of Post's instance methods, so
it can't trigger the callbacks itself.

What we really want is for the transaction itself to hold weak
references to the objects within the transaction. So those objects can
be GC'd, but if they are not GC'd then the transaction can iterate them
and execute their callbacks.

I've looked into WeakRef implementations that are available. On 1.9.3,
the stdlib weakref library is broken and we shouldn't use it.

There is a better implementation here:

https://github.com/bdurand/ref/blob/master/lib/ref/weak_reference/pure_ruby.rb

We could use that, either by pulling in the gem or just copying the code
in, but it still suffers from the limitation that it uses ObjectSpace
finalizers.

In my testing, this finalizers make GC quite expensive:
https://gist.github.com/3722432

Ruby 2.0 will have a native WeakRef implementation (via
ObjectSpace::WeakMap), hence won't be reliant on finalizers:
http://bugs.ruby-lang.org/issues/4168

So the ultimate solution will be for everyone to use Ruby 2.0, and for
us to just use ObjectSpace::WeakMap.

In the meantime, we have basically 3 options:

The first is to leave it as it is.

The second is to use a finalizer-based weakref implementation and take
the GC perf hit.

The final option is to store object ids rather than the actual objects.
Then use ObjectSpace._id2ref to deference the objects at the end of the
transaction, if they exist. This won't stop memory use growing within
the transaction, but it'll grow more slowly.

I benchmarked the performance of _id2ref this if the object does or does
not exist: https://gist.github.com/3722550

If it does exist it seems decent, but it's hugely more expensive if it
doesn't, probably because we have to do the rescue nil.

Probably most of the time the objects will exist. However the point of
doing this optimisation is to allow people to create a large number of
objects inside a transaction and have them be GC'd. So for that use
case, we'd be replacing one problem with another. I'm not sure which of
the two problems is worse.

My feeling is that we should just leave this for now and come back to it
when Ruby 2.0 is out.

I'm going to revert your commit because I can't see how it solves this.
Hope you don't mind... if I've misunderstood then let me know!

Jon

Having column related schema dumper code in the AbstractAdapter. The
code remains the same, but by placing it in the AbstractAdapter, we can
then overwrite it with Adapter specific methods that will help with
Adapter specific data types.

The goal of moving this code here is to create a new migration key for
PostgreSQL's array type. Since any datatype can be an array, the goal is
to have ':array => true' as a migration option, turning the datatype
into an array. I've implemented this in postgres_ext, the syntax is
shown here: https://github.com/dockyard/postgres_ext#arrays

Adds array migration support

Adds array_test.rb outlining the test cases for array data type
Adds pg_array_parser to Gemfile for testing
Adds pg_array_parser to postgresql_adapter (unused in this commit)

Adds schema dump support for arrays

Adds postgres array type casting support

Updates changelog, adds note for inet and cidr support, which I forgot to add before

Removing debugger, Adds pg_array_parser to JRuby platform

Removes pg_array_parser requirement, creates ArrayParser module used by
PostgreSQLAdapter

transaction.