Added Sherlock, a custom profiling tool for GitLab

Sherlock will be a new GitLab specific tool for measuring the
performance of Rails requests (and SideKiq jobs at some point). Some of
the things that are currently tracked:

* SQL queries along with their timings, backtraces and query plans
  (using "EXPLAIN ANALYZE" for PostgreSQL and regular "EXPLAIN" for
  MySQL)
* Timings of application files (including views) on a per line basis
* Some meta data such as the request method, path, total duration, etc

More tracking (e.g. Rugged or gitlab-shell timings) might be added in
the future.

Sherlock will replace any existing tools we have used so far (e.g.
active_record_query_trace and rack-mini-profiler), hence the
corresponding Gems have been removed from the Gemfile.

Sherlock can be enabled by starting Rails as following:

    ENABLE_SHERLOCK=1 bundle exec rails s

Recorded transactions can be found at `/sherlock/transactions`.

8 files changed, 388 insertions, 0 deletions

diff --git a/lib/gitlab/sherlock/collection.rb b/lib/gitlab/sherlock/collection.rb
new file mode 100644
index 00000000000..accdc6469bc
--- /dev/null
+++ b/lib/gitlab/sherlock/collection.rb
@@ -0,0 +1,42 @@
+module Gitlab
+  module Sherlock
+    class Collection
+      include Enumerable
+
+      def initialize
+        @transactions = []
+        @mutex = Mutex.new
+      end
+
+      def add(transaction)
+        synchronize { @transactions << transaction }
+      end
+
+      alias_method :<<, :add
+
+      def each(&block)
+        synchronize { @transactions.each(&block) }
+      end
+
+      def clear
+        synchronize { @transactions.clear }
+      end
+
+      def empty?
+        synchronize { @transactions.empty? }
+      end
+
+      def find_transaction(id)
+        find { |trans| trans.id == id }
+      end
+
+      def newest_first
+        sort { |a, b| b.finished_at <=> a.finished_at }
+      end
+
+      def synchronize(&block)
+        @mutex.synchronize(&block)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/file_sample.rb b/lib/gitlab/sherlock/file_sample.rb
new file mode 100644
index 00000000000..7a220de9abc
--- /dev/null
+++ b/lib/gitlab/sherlock/file_sample.rb
@@ -0,0 +1,27 @@
+module Gitlab
+  module Sherlock
+    class FileSample
+      attr_reader :id, :file, :line_samples, :events, :duration
+
+      def initialize(file, line_samples, duration, events)
+        @id = SecureRandom.uuid
+        @file = file
+        @line_samples = line_samples
+        @duration = duration
+        @events = events
+      end
+
+      def relative_path
+        @relative_path ||= @file.gsub(/^#{Rails.root.to_s}\/?/, '')
+      end
+
+      def to_param
+        @id
+      end
+
+      def source
+        @source ||= File.read(@file)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/line_profiler.rb b/lib/gitlab/sherlock/line_profiler.rb
new file mode 100644
index 00000000000..a191b1e646d
--- /dev/null
+++ b/lib/gitlab/sherlock/line_profiler.rb
@@ -0,0 +1,60 @@
+module Gitlab
+  module Sherlock
+    class LineProfiler
+      # The minimum amount of time that has to be spent in a file for it to be
+      # included in a list of samples.
+      MINIMUM_DURATION = 10.0
+
+      def profile(&block)
+        if RUBY_ENGINE == 'ruby'
+          profile_mri(&block)
+        else
+          raise NotImplementedError,
+            'Line profiling is not supported on this platform'
+        end
+      end
+
+      def profile_mri
+        retval  = nil
+        samples = lineprof(/^#{Rails.root.to_s}/) { retval = yield }
+
+        file_samples = aggregate_rblineprof(samples)
+
+        [retval, file_samples]
+      end
+
+      # Returns an Array of file samples based on the output of rblineprof.
+      def aggregate_rblineprof(lineprof_stats)
+        samples = []
+
+        lineprof_stats.each do |(file, stats)|
+          source_lines = File.read(file).each_line.to_a
+          line_samples = []
+
+          total_duration = microsec_to_millisec(stats[0][0])
+          total_events   = stats[0][2]
+
+          next if total_duration <= MINIMUM_DURATION
+
+          stats[1..-1].each_with_index do |data, index|
+            next unless source_lines[index]
+
+            duration = microsec_to_millisec(data[0])
+            events   = data[2]
+
+            line_samples << LineSample.new(duration, events)
+          end
+
+          samples << FileSample.
+            new(file, line_samples, total_duration, total_events)
+        end
+
+        samples
+      end
+
+      def microsec_to_millisec(microsec)
+        microsec / 1000.0
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/line_sample.rb b/lib/gitlab/sherlock/line_sample.rb
new file mode 100644
index 00000000000..38df7a88e4e
--- /dev/null
+++ b/lib/gitlab/sherlock/line_sample.rb
@@ -0,0 +1,20 @@
+module Gitlab
+  module Sherlock
+    class LineSample
+      attr_reader :duration, :events
+
+      def initialize(duration, events)
+        @duration = duration
+        @events = events
+      end
+
+      def percentage_of(total_duration)
+        (duration.to_f / total_duration) * 100.0
+      end
+
+      def majority_of?(total_duration)
+        percentage_of(total_duration) >= 30
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/location.rb b/lib/gitlab/sherlock/location.rb
new file mode 100644
index 00000000000..8c0b77dce1a
--- /dev/null
+++ b/lib/gitlab/sherlock/location.rb
@@ -0,0 +1,22 @@
+module Gitlab
+  module Sherlock
+    class Location
+      attr_reader :path, :line
+
+      SHERLOCK_DIR = File.dirname(__FILE__)
+
+      def self.from_ruby_location(location)
+        new(location.path, location.lineno)
+      end
+
+      def initialize(path, line)
+        @path = path
+        @line = line
+      end
+
+      def application?
+        @path.start_with?(Rails.root.to_s) && !path.start_with?(SHERLOCK_DIR)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/middleware.rb b/lib/gitlab/sherlock/middleware.rb
new file mode 100644
index 00000000000..fca7be858eb
--- /dev/null
+++ b/lib/gitlab/sherlock/middleware.rb
@@ -0,0 +1,36 @@
+module Gitlab
+  module Sherlock
+    # Rack middleware used for tracking request metrics.
+    class Middleware
+      CONTENT_TYPES = /text\/html|application\/json/i
+
+      IGNORE_PATHS = %r{^/sherlock}
+
+      def initialize(app)
+        @app = app
+      end
+
+      def call(env)
+        if instrument?(env)
+          call_with_instrumentation(env)
+        else
+          @app.call(env)
+        end
+      end
+
+      def call_with_instrumentation(env)
+        trans = Transaction.new(env['REQUEST_METHOD'], env['REQUEST_URI'])
+        retval = trans.run { @app.call(env) }
+
+        Sherlock.collection.add(trans)
+
+        retval
+      end
+
+      def instrument?(env)
+        !!(env['HTTP_ACCEPT'] =~ CONTENT_TYPES &&
+           env['REQUEST_URI'] !~ IGNORE_PATHS)
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/query.rb b/lib/gitlab/sherlock/query.rb
new file mode 100644
index 00000000000..af76e6fd2bf
--- /dev/null
+++ b/lib/gitlab/sherlock/query.rb
@@ -0,0 +1,96 @@
+module Gitlab
+  module Sherlock
+    class Query
+      attr_reader :id, :query, :started_at, :finished_at, :backtrace
+
+      PREFIX_NEWLINE = /
+        \s+(FROM
+          |(LEFT|RIGHT)?INNER\s+JOIN
+          |(LEFT|RIGHT)?OUTER\s+JOIN
+          |WHERE
+          |AND
+          |GROUP\s+BY
+          |ORDER\s+BY
+          |LIMIT
+          |OFFSET)\s+
+      /ix
+
+      def self.new_with_bindings(query, bindings, started_at, finished_at)
+        bindings.each_with_index do |(column, value), index|
+          quoted_value = ActiveRecord::Base.connection.quote(value)
+
+          query = query.gsub("$#{index + 1}", quoted_value)
+        end
+
+        new(query, started_at, finished_at)
+      end
+
+      def initialize(query, started_at, finished_at)
+        @id = SecureRandom.uuid
+        @query = query
+        @started_at = started_at
+        @finished_at = finished_at
+        @backtrace = caller_locations.map do |loc|
+          Location.from_ruby_location(loc)
+        end
+
+        unless @query.end_with?(';')
+          @query += ';'
+        end
+      end
+
+      def duration
+        @duration ||= (@finished_at - @started_at) * 1000.0
+      end
+
+      def to_param
+        @id
+      end
+
+      def formatted_query
+        @formatted_query ||= format_sql(@query)
+      end
+
+      def last_application_frame
+        @last_application_frame ||= @backtrace.find(&:application?)
+      end
+
+      def application_backtrace
+        @application_backtrace ||= @backtrace.select(&:application?)
+      end
+
+      def explain
+        unless @explain
+          ActiveRecord::Base.connection.transaction do
+            @explain = raw_explain(@query).values.flatten.join("\n")
+
+            # Roll back any queries that mutate data so we don't mess up
+            # anything when running explain on an INSERT, UPDATE, DELETE, etc.
+            raise ActiveRecord::Rollback
+          end
+        end
+
+        @explain
+      end
+
+      private
+
+      def raw_explain(query)
+        if Gitlab::Database.postgresql?
+          explain = "EXPLAIN ANALYZE #{query};"
+        else
+          explain = "EXPLAIN #{query};"
+        end
+
+        ActiveRecord::Base.connection.execute(explain)
+      end
+
+      def format_sql(query)
+        query.each_line.
+          map { |line| line.strip }.
+          join("\n").
+          gsub(PREFIX_NEWLINE) { "\n#{$1} " }
+      end
+    end
+  end
+end
diff --git a/lib/gitlab/sherlock/transaction.rb b/lib/gitlab/sherlock/transaction.rb
new file mode 100644
index 00000000000..5cb3e86aa4e
--- /dev/null
+++ b/lib/gitlab/sherlock/transaction.rb
@@ -0,0 +1,85 @@
+module Gitlab
+  module Sherlock
+    class Transaction
+      attr_reader :id, :type, :path, :queries, :file_samples, :started_at,
+        :finished_at
+
+      def initialize(type, path)
+        @id = SecureRandom.uuid
+        @type = type
+        @path = path
+        @duration = 0
+        @queries = []
+        @file_samples = []
+        @started_at = nil
+        @finished_at = nil
+        @thread = Thread.current
+      end
+
+      def run
+        @started_at = Time.now
+
+        subscriber = subscribe_to_active_record
+
+        retval = profile_lines { yield }
+
+        @finished_at = Time.now
+
+        ActiveSupport::Notifications.unsubscribe(subscriber)
+
+        retval
+      end
+
+      def duration
+        @started_at && @finished_at ? @finished_at - @started_at : 0
+      end
+
+      def to_param
+        @id
+      end
+
+      def sorted_queries
+        @queries.sort { |a, b| b.duration <=> a.duration }
+      end
+
+      def sorted_file_samples
+        @file_samples.sort { |a, b| b.duration <=> a.duration }
+      end
+
+      def find_query(id)
+        @queries.find { |query| query.id == id }
+      end
+
+      def find_file_sample(id)
+        @file_samples.find { |sample| sample.id == id }
+      end
+
+      def track_query(query, bindings, start, finish)
+        @queries << Query.new_with_bindings(query, bindings, start, finish)
+      end
+
+      def profile_lines
+        retval = nil
+
+        if Sherlock.enable_line_profiler?
+          retval, @file_samples = LineProfiler.new.profile { yield }
+        else
+          retval = yield
+        end
+
+        retval
+      end
+
+      def subscribe_to_active_record
+        ActiveSupport::Notifications.subscribe('sql.active_record') do |_, start, finish, _, data|
+          # In case somebody uses a multi-threaded server locally (e.g. Puma) we
+          # _only_ want to track queries that originate from the transaction
+          # thread.
+          next unless Thread.current == @thread
+
+          track_query(data[:sql].strip, data[:binds], start, finish)
+        end
+      end
+    end
+  end
+end