shopify / activerecord-pedantmysql2-adapter Goto Github PK

While setting up cod-app for cloud, I realized that rails dbconsole would fail with unknown command-line client for #{database_name}.

I dug through the dbconsole source and attached a few puts to the dbconsole in cluster and observed the following output:

The regex match on the case predicate in dbconsole.rb will always fail since when /^(jdbc)?mysql/ begins with pedant, not mysql.

Not sure if this is worthy of a fix since I don't know how often rails dbconsole gets used, but a simple solution seems to be simply renaming the adapter to mysql_pedant.

cc @casperisfine, @goldenson

Currently EXPLAIN queries fail with this adapter installed because on recent versions of MySQL, the server generates a warning with level = "Note" and code = 1003 because the EXPLAIN query is optimized away. This makes sense because an EXPLAIN query doesn't actually execute the query it is explaining.

Example output when calling EXPLAIN SELECT 1:

[1] pry(main)> ActiveRecord::Base.connection.exec_query("EXPLAIN SELECT 1;")
  SQL (1.1ms)  EXPLAIN SELECT 1;
{:severity=>:warn, :messages=>["/* select#1 */ select 1 AS `1`"], :query=>"EXPLAIN SELECT 1;"}
MysqlWarning: /* select#1 */ select 1 AS `1`
from /Users/ryanseys/repo/pedant_mysql2.rb:14:in `block in <main>'

[2] pry(main)> ActiveRecord::Base.connection.exec_query("SHOW WARNINGS")
  SQL (15.9ms)  SHOW WARNINGS
#<ActiveRecord::Result:0x000000010d8becb0 @columns=["Level", "Code", "Message"], @rows=[["Note", 1003, "/* select#1 */ select 1 AS `1`"]], @hash_rows=nil, @column_types={}>

There's currently no great way to ignore these queries because PedantMySQL2.ignore can only ignore based on warning messages, and does not ignore based on warning code or warning level.

Current workaround

The current workaround I found was to exit the on_warning lambda early if the warning meets the conditions of an EXPLAIN query.

PedantMysql2.on_warning = lambda do |warning|
  return if warning.level == "Note" && warning.code == 1003 && warning.query.start_with?("EXPLAIN")

  raise warning
end

There's a few different ways I think we could solve this:

Option 1: Hardcode the ignore of these EXPLAIN queries into the default behavior of this gem

Similar to how drop_table queries are already ignored, we could ignore these warnings by default. Also not backward compatible per-se because perhaps someone wants to catch these warnings?

That said, these warnings are safe to ignore because they are just a warning that the MySQL query optimizer has optimized the query away and did not execute it, which is to be expected for EXPLAIN queries. It also follows a similar behavior to the drop_table behavior where a table cannot be found -- the query optimizer is doing the same thing in this case by not executing the query because the table does not exist.

I've implemented this in #24

Option 2: Introduce PedantMySQL.ignore_if(&block)

Introduce a way to ignore based on the contents of a block. This would be backward compatible as it is a new method, but it would require anyone who wants this functionality to manually implement it, which is annoying and probably means that people are more likely to not implement this correctly, and adds additional overhead to all developers using this gem.

PedantMySQL2.ignore_if do |warning|
  warning.code == 1003 && warning.level == "Note" && warning.query.start_with?("EXPLAIN")
end

Option 3: PedantMySQL.ignore(&block)

Re-use the existing ignore but allow it to take a block. Not backward compatible as it reuses the same method that already exists. Probably the worst of the three options.

PedantMySQL2.ignore do |warning|
  warning.code == 1003 && warning.level == "Note" && warning.query.start_with?("EXPLAIN")
end

I added the gem, bundled and changed the adapter in my datbase.yml. Then, I get this when starting a console:

/gems/activesupport-3.2.21/lib/active_support/dependencies.rb:251:in require': Please install the pedantmysql2 adapter:gem install activerecord-pedantmysql2-adapter` (cannot load such file -- active_record/connection_adapters/pedantmysql2_adapter) (LoadError)

Seems to work fine in a rails 4.1 app though.... is rails 3.x supported?