Merge pull request #6197 from blakesmith/connection_adapters_without_explain_support

Don't run explain on slow queries for database adapters that don't support it

2 files changed, 14 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/explain.rb b/activerecord/lib/active_record/explain.rb
index bdccf535ea..236834fd84 100644
--- a/activerecord/lib/active_record/explain.rb
+++ b/activerecord/lib/active_record/explain.rb
@@ -11,11 +11,12 @@ module ActiveRecord
       end
     end
 
-    # If auto explain is enabled, this method triggers EXPLAIN logging for the
-    # queries triggered by the block if it takes more than the threshold as a
-    # whole. That is, the threshold is not checked against each individual
-    # query, but against the duration of the entire block. This approach is
-    # convenient for relations.
+    # If the database adapter supports explain and auto explain is enabled,
+    # this method triggers EXPLAIN logging for the queries triggered by the
+    # block if it takes more than the threshold as a whole. That is, the
+    # threshold is not checked against each individual query, but against the
+    # duration of the entire block. This approach is convenient for relations.
+
     #
     # The available_queries_for_explain thread variable collects the queries
     # to be explained. If the value is nil, it means queries are not being
@@ -26,7 +27,7 @@ module ActiveRecord
 
       threshold = auto_explain_threshold_in_seconds
       current   = Thread.current
-      if threshold && current[:available_queries_for_explain].nil?
+      if connection.supports_explain? && threshold && current[:available_queries_for_explain].nil?
         begin
           queries = current[:available_queries_for_explain] = []
           start = Time.now
diff --git a/activerecord/lib/active_record/railtie.rb b/activerecord/lib/active_record/railtie.rb
index 13b7c6e214..055d27d85c 100644
--- a/activerecord/lib/active_record/railtie.rb
+++ b/activerecord/lib/active_record/railtie.rb
@@ -83,6 +83,13 @@ module ActiveRecord
       end
     end
 
+    initializer "active_record.validate_explain_support" do |app|
+      if app.config.active_record[:auto_explain_threshold_in_seconds] &&
+        !ActiveRecord::Base.connection.supports_explain?
+        warn "auto_explain_threshold_in_seconds is set but will be ignored because your adapter does not support this feature. Please unset the configuration to avoid this warning."
+      end
+    end
+
     # Expose database runtime to controller for logging.
     initializer "active_record.log_runtime" do |app|
       require "active_record/railties/controller_runtime"