don't count ignored redis errors in stats

refs CNVS-15570

test plan: trigger an ignored redis error, such as running
`Canvas.redis.renamenx('no-such-key', 'new-key')` in console, and verify
that rails doesn't log a 'Failure handling redis' message, or send
anything to statsd.

Change-Id: Ie4480fcf053d626ba8dbdf26672b18815267fa86
Reviewed-on: https://gerrit.instructure.com/41805
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>
QA-Review: Brian Palmer <brianp@instructure.com>

lib/canvas/redis.rb

@@ -49,10 +49,6 @@ module Canvas::Redis
     raise reply if reply.is_a?(Exception)
     reply
   rescue ::Redis::BaseConnectionError, SystemCallError, ::Redis::CommandError => e
-    CanvasStatsd::Statsd.increment("redis.errors.all")
-    CanvasStatsd::Statsd.increment("redis.errors.#{CanvasStatsd::Statsd.escape(redis_name)}")
-    Rails.logger.error "Failure handling redis command on #{redis_name}: #{e.inspect}"
-
     # We want to rescue errors such as "max number of clients reached", but not
     # actual logic errors such as trying to evalsha a script that doesn't
     # exist.
@@ -62,6 +58,10 @@ module Canvas::Redis
       raise
     end
 
+    CanvasStatsd::Statsd.increment("redis.errors.all")
+    CanvasStatsd::Statsd.increment("redis.errors.#{CanvasStatsd::Statsd.escape(redis_name)}")
+    Rails.logger.error "Failure handling redis command on #{redis_name}: #{e.inspect}"
+
     if self.ignore_redis_failures?
       ErrorReport.log_exception(:redis, e)
       last_redis_failure[redis_name] = Time.now

spec/lib/canvas/redis_spec.rb

@@ -66,6 +66,8 @@ describe "Canvas::Redis" do
     end
 
     it "should pass through other command errors" do
+      CanvasStatsd::Statsd.expects(:increment).never
+
       Redis::Client.any_instance.expects(:write).raises(Redis::CommandError.new("NOSCRIPT No matching script. Please use EVAL.")).once
       expect { Canvas.redis.evalsha('xxx') }.to raise_error(Redis::CommandError)