Improve performance to call Mysql2::Result#each and Mysql2::Result#fields

[Watson1978]

This PR will reduce the time to call Mysql2::Result#each and Mysql2::Result#fields.

If table records are small enough, the performance will improve as following.

Mysql2::Result#each : 901.633k -> 1.550M (1.71x faster)
Mysql2::Result#fields : 3.779M -> 6.233M (1.65x faster)

1. Use rb_ivar_get/rb_ivar_set to improve performance

• By convert C-string to Ruby string ID each time, it will take a slightly time to call method each time.
  This patch will catch the Ruby string ID to cut off the time.

2. Check only whether block was given

• rb_scan_args(argc, argv, "01&", ...) will generate Proc object from block. However, the object has used to only check whether block was given. To remove redundant object generating, this patch will use rb_block_given_p() to check whether block was given.

Environment

• CPU : Intel(R) Core(TM) i5-3210M CPU @ 2.50GHz
• OS : Ubuntu 18.10
• Compiler : gcc version 8.3.0

Before changing

Warming up --------------------------------------
               query   886.000  i/100ms
                each    67.339k i/100ms
              fields   195.612k i/100ms
Calculating -------------------------------------
               query      9.385k (± 4.5%) i/s -     46.958k in   5.016539s
                each    901.633k (± 0.2%) i/s -      4.512M in   5.003951s
              fields      3.779M (± 0.2%) i/s -     18.974M in   5.021533s

After changing

Warming up --------------------------------------
               query   864.000  i/100ms
                each   106.916k i/100ms
              fields   251.255k i/100ms
Calculating -------------------------------------
               query      9.457k (± 3.8%) i/s -     47.520k in   5.032949s
                each      1.550M (± 0.3%) i/s -      7.805M in   5.037029s
              fields      6.233M (± 0.1%) i/s -     31.407M in   5.039049s

Benchmarks

require 'benchmark/ips'
require 'mysql2'

def setup_database(client)
  # client.query('create database benchmark')
  sql = <<SQL
create table benchmark.users (
  id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
  name text,
  email text,
  created_at datetime,
  updated_at datetime
)
SQL
  client.query(sql)

  5.times do |i|
    client.query("insert into benchmark.users (name, email, created_at, updated_at) values ('foo', '[email protected]', '#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}', '#{Time.now.strftime("%Y-%m-%d %H:%M:%S")}')")
  end
end


client = Mysql2::Client.new(
  :host     => "127.0.0.1",
  :username => "root",
  :password => "",
  :database => "benchmark"
)

# setup_database(client)

Benchmark.ips do |x|
  query = 'select * from users'.freeze
  x.report "query" do
    client.query(query)
  end

  results = client.query(query)
  x.report "each" do
    results.each {}
  end

  x.report "fields" do
    results.fields
  end
end

[sodabrew]

Great explanation that actually capturing the block will generate a Proc object that is never called!

To really clarify this code, I suggest a deeper change:

1. Add a comment above rb_scan_args that says something like "A block can be passed to this method, but since we don't call the block directly from C, we don't need to capture it into a variable here with the "&" scan arg"

2. Remove the block variable entirely.

3. Replace args.block_given = block; on line 890 with args.block_given = rb_block_given_p()

(Adjust the data type of args.block_given to match the return value of rb_block_given_p() if needed)

[Watson1978]

@sodabrew Thank you for your review!! I fixed a patch with your idea at a734989

[sodabrew]

This is great work, thank you! One comment in the review.