Before:

```
   (16.4ms)  TRUNCATE TABLE `author_addresses`
   (20.5ms)  TRUNCATE TABLE `authors`
   (19.4ms)  TRUNCATE TABLE `posts`
```

After:

```
  Truncate Tables (19.5ms)  TRUNCATE TABLE `author_addresses`;
TRUNCATE TABLE `authors`;
TRUNCATE TABLE `posts`
```

https://buildkite.com/rails/rails/builds/59622#924dff9d-85c2-4946-b264-a7e6ce01432c/122-130

This is to easier make `truncate_tables` to bulk statements.

We as Arm Treasure Data are using Optimizer Hints with a monkey patch
(https://gist.github.com/kamipo/4c8539f0ce4acf85075cf5a6b0d9712e),
especially in order to use `MAX_EXECUTION_TIME` (refer #31129).

Example:

```ruby
class Job < ApplicationRecord
  default_scope { optimizer_hints("MAX_EXECUTION_TIME(50000) NO_INDEX_MERGE(jobs)") }
end
```

Optimizer Hints is supported not only for MySQL but also for most
databases (PostgreSQL on RDS, Oracle, SQL Server, etc), it is really
helpful to turn heavy queries for large scale applications.

This reverts commit 65f2eeaa.

Follow up #35573

This commit addresses the issue in
https://github.com/rails/rails/issues/35543 by making note of the
growing primary key issue with `create_or_find_by`.

Useful to not query for indexes when an application uses schema cache.

Ref https://github.com/rails/rails/pull/35546

Not looking for other contributions like this, but I took the liberty
since I was already working on this.

YAML has been used to serialize the schema cache ever since 2016 with
Rails 5.1: 4c00c6ed

The `Row` class is no longer used since d956772b.

Staled `@default_timezone` would cause an error on `reconnect!` after
`disconnect!`.

https://buildkite.com/rails/rails/builds/59495#23be8079-3a4f-4375-9991-0a6f874554f2

Steps to reproduce:

```
% ARCONN=postgresql bin/test test/cases/adapter_test.rb test/cases/base_test.rb -n "/(?:test_attributes_on_dummy_time|test_reconnect_after_a_disconnect)$/" --seed 15849
Using postgresql
Run options: -n "/(?:test_attributes_on_dummy_time|test_reconnect_after_a_disconnect)$/" --seed 15849

# Running:

.
E

Error:
ActiveRecord::AdapterTestWithoutTransaction#test_reconnect_after_a_disconnect:
NoMethodError: undefined method `add_coder' for #<PG::TypeMapAllStrings:0x00007f85ab9dd5b8>
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:866:in `update_typemap_for_default_timezone'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:652:in `exec_no_cache'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:636:in `execute_and_clear'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:894:in `add_pg_decoders'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:744:in `connect'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:285:in `rescue in block in reconnect!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:281:in `block in reconnect!'
    /Users/kamipo/.rbenv/versions/2.6.1/lib/ruby/2.6.0/monitor.rb:230:in `mon_synchronize'
    /Users/kamipo/src/github.com/rails/rails/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb:280:in `reconnect!'
    /Users/kamipo/src/github.com/rails/rails/activerecord/test/cases/adapter_test.rb:465:in `block in <class:AdapterTestWithoutTransaction>'
```

* Update RAILS_VERSION
* Bundle
* rake update_versions
* rake changelog:header

Sample example ->

Before:

prathamesh@Prathameshs-MacBook-Pro-2 blog *$ rails server thin
DEPRECATION WARNING: Passing the Rack server name as a regular argument is deprecated
and will be removed in the next Rails version. Please, use the -u
option instead.

After:

prathamesh@Prathameshs-MacBook-Pro-2 squish_app *$ rails server thin
DEPRECATION WARNING: Passing the Rack server name as a regular argument is deprecated and will be removed in the next Rails version. Please, use the -u option instead.

change the line to check an attribute has user-defined type

ref: https://github.com/rails/rails/pull/35320#discussion_r257924552

check query attribute method is working when given value does not respond to to_i method

It is to work that on `reconnect!` after `disconnect!`.

https://buildkite.com/rails/rails/builds/59378#1efea538-cfca-4d43-8b7e-ae78e97227c8

It is to work that on `reconnect!` after `disconnect!`

Details in https://github.com/rails/rails/issues/35519

In short, MySQL and Sqlite3 allow a record to be both inserted _and_ replaced in the same operation. Postgres (and the SQL-2003 rules for MERGE) do not.

Postgres's rationale seems to be that the operation would be nondeterministic.

I think it's OK for Rails users to have a different experience with this feature depending on their database; but I think you should be able to follow the examples in the docs on any database.

I've found the skewness of delegation methods between `except` and
`only` in a88b6f25.

The `only` method is closely similar with `except` as `SpawnMethods`.

https://github.com/rails/rails/blob/e056b9bfb07c4eb3bcc6672d885aadd72bec574f/activerecord/lib/active_record/relation/spawn_methods.rb#L53-L67

It is preferable both behaves the same way.

This makes to ease testing `QUERYING_METHODS`.

Foreign keys could be created to the same table.
So `remove_foreign_key :from_table, :to_table` is sometimes ambiguous.
This allows `remove_foreign_key` to remove the select one on the same
table with giving both `to_table` and `options`.

This change adds a new method that loads the YAML for the database
config without parsing the ERB. This may seem odd but bear with me:

When we added the ability to have rake tasks for multiple databases we
started looping through the configurations to collect the namespaces so
we could do `rake db:create:my_second_db`. See #32274.

This caused a problem where if you had `Rails.config.max_threads` set in
your database.yml it will blow up because the environment that defines
`max_threads` isn't loaded during `rake -T`. See #35468.

We tried to fix this by adding the ability to just load the YAML and
ignore ERB all together but that caused a bug in GitHub's YAML loading
where if you used multi-line ERB the YAML was invalid. That led us to
reverting some changes in #33748.

After trying to resolve this a bunch of ways `@tenderlove` came up with
replacing the ERB values so that we don't need to load the environment
but we also can load the YAML.

This change adds a DummyCompiler for ERB that will replace all the
values so we can load the database yaml and create the rake tasks.
Nothing else uses this method so it's "safe".

DO NOT use this method in your application.

Fixes #35468

Since #23461, all adapters supports prepared statements, so that clears
the prepared statements cache is no longer database specific.

Actually, I struggled to identify the cause of random CI failure in
#23461, that was missing `@statements.clear` in `clear_cache!`.

This extracts `clear_cache!` to ensure the common concerns in the
abstract adapter.

Adds a method to ActiveRecord allowing records to be inserted in bulk without instantiating ActiveRecord models. This method supports options for handling uniqueness violations by skipping duplicate records or overwriting them in an UPSERT operation.

ActiveRecord already supports bulk-update and bulk-destroy actions that execute SQL UPDATE and DELETE commands directly. It also supports bulk-read actions through `pluck`. It makes sense for it also to support bulk-creation.

* Add `ActiveRecord::Base.connection.truncate` for SQLite3 adapter.

SQLite doesn't support `TRUNCATE TABLE`, but SQLite3 adapter can support
`ActiveRecord::Base.connection.truncate` by using `DELETE FROM`.

`DELETE` without `WHERE` uses "The Truncate Optimization",
see https://www.sqlite.org/lang_delete.html.

* Add `rails db:seed:replant` that truncates database tables and loads the seeds

Closes #34765

In MySQL, the default collation is case insensitive. Since the
uniqueness validator enforces case sensitive comparison by default, it
frequently causes mismatched collation issues (performance, weird
behavior, etc) to MySQL users.

https://grosser.it/2009/12/11/validates_uniqness_of-mysql-slow/
https://github.com/rails/rails/issues/1399
https://github.com/rails/rails/pull/13465
https://github.com/gitlabhq/gitlabhq/commit/c1dddf8c7d947691729f6d64a8ea768b5c915855
https://github.com/huginn/huginn/pull/1330#discussion_r55152573

I'd like to deprecate the implicit default enforcing since I frequently
experienced the problems in code reviews.

Note that this change has no effect to sqlite3, postgresql, and
oracle-enhanced adapters which are implemented as case sensitive by
default, only affect to mysql2 adapter (I can take a work if sqlserver
adapter will support Rails 6.0).