Fix elapsed time calculations

I've found a few places in Rails code base where I think it makes sense
to calculate elapsed time more precisely by using
`Concurrent.monotonic_time`:

- Fix calculation of elapsed time in `ActiveSupport::Cache::MemoryStore#prune`
- Fix calculation of elapsed time in
  `ActiveRecord::ConnectionAdapters::ConnectionPool::Queue#wait_poll`
- Fix calculation of elapsed time in
  `ActiveRecord::ConnectionAdapters::ConnectionPool#attempt_to_checkout_all_existing_connections`
- Fix calculation of elapsed time in `ActiveRecord::ConnectionAdapters::Mysql2Adapter#explain`

See
https://docs.ruby-lang.org/en/2.5.0/Process.html#method-c-clock_gettime
https://blog.dnsimple.com/2018/03/elapsed-time-with-ruby-the-right-way

Related to 7c4542146f0dde962205e5a90839349631ae60fb

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
index 7b69a63f6e..569c146f92 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb
@@ -166,9 +166,9 @@ module ActiveRecord
 
       def explain(arel, binds = [])
         sql     = "EXPLAIN #{to_sql(arel, binds)}"
-        start   = Time.now
+        start   = Concurrent.monotonic_time
         result  = exec_query(sql, "EXPLAIN", binds)
-        elapsed = Time.now - start
+        elapsed = Concurrent.monotonic_time - start
 
         MySQL::ExplainPrettyPrinter.new.pp(result, elapsed)
       end