From 33d09dbb3b256fb824831a229abdb3189f168135 Mon Sep 17 00:00:00 2001
From: Nick LaMuro <nicklamuro@gmail.com>
Date: Mon, 11 Feb 2019 13:14:18 -0600
Subject: [PATCH] [Service#power_state] Avoid update if values match

As part of the getter for `Service#power_state`, avoid calling an
`update_attributes` if the value is already what we are going to update
it to.

This avoids not only some SQL queries, but some YAML serialization that
slows down API requests and reports that use this `virtual_attribute`.

Benchmarks:
-----------

These benchmarks are done against the API doing the following request:

```
url: /api/services
attributes:
  expand: resources
  attributes:
    -picture
    - picture.image_href
    - chargeback_report
    - evm_owner.userid
    - v_total_vms
    - power_state
    - all_service_children
    - tags
  filter[]:      ancestry=null
  sort_by:       created_at
  sort_options:  nil
  sort_order:    desc
  limit:         20
  offset:        0
```

And about half of the attributes need to trigger an update.  Because of
the way the code is configured and that the metrics were taken against a
database that is detached from the provider (the `power_states_match?`
call is consistent every time as a result), this happens consistently
across runs.

**Before**

|   ms | queries | query (ms) | rows |
| ---: |    ---: |       ---: | ---: |
| 2060 |     322 |        152 | 1627 |
|  799 |     321 |      132.5 |  196 |
|  839 |     321 |      134.2 |  196 |

**After**

|   ms | queries | query (ms) | rows |
| ---: |    ---: |       ---: | ---: |
| 1976 |     290 |        164 | 1625 |
|  675 |     289 |      128.4 |  194 |
|  686 |     289 |      128.4 |  194 |
---
 app/models/service.rb | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/app/models/service.rb b/app/models/service.rb
index 807262235a2..f8fb100f364 100644
--- a/app/models/service.rb
+++ b/app/models/service.rb
@@ -262,7 +262,9 @@ def map_power_states(action)
   end
 
   def update_power_status(action)
-    options[:power_status] = "#{action}_complete"
+    expected_status = "#{action}_complete"
+    return true if options[:power_status] == expected_status
+    options[:power_status] = expected_status
     update_attributes(:options => options)
   end