`insert`, `update`, `delete`, and `exec_query` have a default value
against `name` and `binds`. But `exec_insert`, `exec_update`, and
`exec_delete` not have. It is an inconvenience and inconsistent.

`current_database` executes a query and `table_comment` is called to all
tables even if a table does not have a comment. Using `current_database`
increases extra queries.

Caching a mutable string causes the following issue.

```
Loading development environment (Rails 5.1.0.alpha)
irb(main):001:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!"
irb(main):002:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!!!"
irb(main):003:0> ActiveRecord::Base.connection.quote_table_name('foo') << '!!'
=> "`foo`!!!!!!"
```

To avoid relying on the connection adapter for type casting binds.

[Rafael Mendonça França + Takeshi AKIMA]

If reuse `QUOTED_TRUE` and `QUOTED_FALSE` without frozen, causing the
following issue.

```
Loading development environment (Rails 5.1.0.alpha)
irb(main):001:0> ActiveRecord::Base.connection.quote(true) << ' foo'
=> "1 foo"
irb(main):002:0> ActiveRecord::Base.connection.quote(true) << ' foo'
=> "1 foo foo"
irb(main):003:0> type = ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString.new
=> #<ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::MysqlString:0x007fd40c15e018 @precision=nil, @scale=nil, @limit=nil>
irb(main):004:0> type.serialize(true) << ' bar'
=> "1 foo foo bar"
irb(main):005:0> type.cast(true) << ' bar'
=> "1 foo foo bar bar"
```

Because `type_cast` against `binds` always requires
`attr.value_for_database` and this pattern appears frequently.

`StatementCache` is hard-coded in `cacheable_query` and be passed
`visitor` and `collector` from connection adapter. Simply it is
enough to pass a collected value.

Where appropriatei, prefer the more concise Regexp#match?,
String#include?, String#start_with?, or String#end_with?

Because `connection#to_sql` does not mutate `binds`.

Address to https://github.com/rails/rails/commit/5a302bf553af0e6fedfc63299fc5cd6e79599ef3#commitcomment-18288388.

Refactored method `ActiveRecord::ConnectionAdapters::PostgreSQL::SchemaStatements#default_sequence_name`

Follow up to #20818.

`retrieve_connection` is passed `spec_name` instead of `klass` since #24844.

- Followup of https://github.com/rails/rails/pull/23179.

Keeps schema migration inserts as a single commit, so we still get all of the
benefits of https://github.com/rails/rails/commit/42dd2336b31a8d98776d039a2b9fd7f834156a78,
but allows for easier git diff-ing. Fixes #25504.

loaded model classes have their connections wrapped in transactions.

See #17776

In Rails 4 config.eager_load was changed to false in the test environment. This
means that model classes that connect to alternate databases with
establish_connection are not loaded at start up. If use_transactional_fixtures
is enabled, transactions are wrapped around the connections that have been
established only at the start of the test suite. So model classes loaded later
don't have transactions causing data created in the alternate database not to
be removed.

This change resolves that by creating a new connection.active_record
notification that gets fired whenever a connection is established. I then added
a subscriber after we set up transactions in the test environment to listen for
additional connections and wrap those in transactions as well.

This includes minor grammar fixes throughout the file.

This way, we aren't racing other threads, so we don't need to re-check
the conditional. And we no longer need to hold the lock while calling
remove (which can choose to make a new connection while we wait).

A concurrent thread may have also detected it to be stale, and already
released (or even reassigned) it by now.

Fixes #25585

A thread can only release a connection if it owns it, or it's owned by a
thread that has died.

Actually schema dumper/creation supports composite primary key (#21614).
Therefore it should not show the warning about composite primary key in
connection adapter.

This change moves the warning to `AttributeMethods::PrimaryKey` and
suppress the warning for habtm join table.

Fixes #25388.

`create_table_info_cache` is used for sharing `create_table_info` both
`table_options` and `foreign_keys`. But `foreign_keys` no longer uses
`create_table_info_cache` by #25307. No need caching anymore.

This was added at c7c3f73f but it never raised because MySQL cannot
create text/blob columns with a default value.

The implementation from abstract/database_statements.rb seems to work just fine.
And with ActiveRecord::Result now implementing an optimized #first method, the
performance concerns previously addressed in
https://github.com/rails/rails/commit/bf79aa4fc14aeb2646331e767038acf0b77e9e7f
should not be an issue.

Fixes #25391

- Followup of https://github.com/rails/rails/commit/1ea6cc11211dc89e3e14b2b641a3cca8a0a91d55.

Fixes #25300.

Currently CI is broken due to 56a61e0c and c4cb6862. This occurred because
the failures are not present on SQLite which is what I normally run
locally before pushing.

The optimizations to our YAML size were dropping mutations, as
`with_type` didn't set the previous value if it'd already been read
(that method was never really designed to be used with values on
individual objects, it was previously only used for defaults). I'm
questioning whether there's a better place to be handling the exclusion
of the type, but this will fix the failing build.

Additionally, there was a bug in `remove_foreign_key` if you passed it
an options hash containing `to_table`. This now occurs whenever removing
a reference, as we always normalize to a hash.

[Sean Griffin & Ryuta Kamizono]

The code incorrectly assumes that the option was written as
`foreign_key: true`, but that is not always the case. This now mirrors
the behavior of reverting `add_foreign_key`. The code was changed to use
kwargs while I was touching it, as well.

This could really use a refactoring to go through the same code paths as
`add_refernce` in the future, so we don't duplicate default values.

Fixes #25169

Follow up of #20815.

```ruby
class CreatePeople < ActiveRecord::Migration[5.0]
  def change
    create_table :people do |t|
      t.integer :int
      t.bigint :bint
      t.text :txt
      t.binary :bin
    end
  end
end
```

Result.

In postgresql and sqlite3 adapters:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```

In mysql2 adapter:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt",  limit: 65535
    t.binary  "bin",  limit: 65535
  end

end
```

After this patch:

```ruby
ActiveRecord::Schema.define(version: 20160531141018) do

  create_table "people", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8mb4" do |t|
    t.integer "int"
    t.bigint  "bint"
    t.text    "txt"
    t.binary  "bin"
  end

end
```