X-Git-Url: https://git.arvados.org/arvados.git/blobdiff_plain/1d5b46697b5d7c68b0bb159fc570ed63c1e3acc3..35c2572761bb060aa1c12f417f97aa9e1ccbe7eb:/apps/workbench/app/controllers/keep_disks_controller.rb

diff --git a/apps/workbench/app/controllers/keep_disks_controller.rb b/apps/workbench/app/controllers/keep_disks_controller.rb
index 345d17f251..bbf18e591b 100644
--- a/apps/workbench/app/controllers/keep_disks_controller.rb
+++ b/apps/workbench/app/controllers/keep_disks_controller.rb
@@ -6,24 +6,45 @@ class KeepDisksController < ApplicationController
   end
 
   def index
-    # Retrieve cache age histogram info
+    # Retrieve cache age histogram info from logs.
+
+    # In the logs we expect to find it in an ordered list with entries
+    # of the form (mtime, disk proportion free).
+
+    # An entry of the form (1388747781, 0.52) means that if we deleted
+    # the oldest non-presisted blocks until we had 52% of the disk
+    # free, then all blocks with an mtime greater than 1388747781
+    # would be preserved.
+
+    # The chart we want to produce, will tell us how much of the disk
+    # will be free if we use a cache age of x days. Therefore we will
+    # produce output specifying the age, cache and persisted. age is
+    # specified in milliseconds. cache is the size of the cache if we
+    # delete all blocks older than age. persistent is the size of the
+    # persisted blocks. It is constant regardless of age, but it lets
+    # us show a stacked graph.
+
+    # Finally each entry in cache_age_histogram is a dictionary,
+    # because that's what our charting package wats.
+
     @cache_age_histogram = []
-    @histogram_date = 0
+    @histogram_pretty_date = nil
     histogram_log = Log.
       filter([[:event_type, '=', 'block-age-free-space-histogram']]).
       order(:created_at => :desc).
+      with_count('none').
       limit(1)
     histogram_log.each do |log_entry|
       # We expect this block to only execute at most once since we
       # specified limit(1)
       @cache_age_histogram = log_entry['properties'][:histogram]
       # Javascript wants dates in milliseconds.
-      @histogram_date = log_entry['event_at'].to_i * 1000
+      histogram_date_ms = log_entry['event_at'].to_i * 1000
       @histogram_pretty_date = log_entry['event_at'].strftime('%b %-d, %Y')
 
       total_free_cache = @cache_age_histogram[-1][1]
       persisted_storage = 1 - total_free_cache
-      @cache_age_histogram.map! { |x| {:age => @histogram_date - x[0]*1000,
+      @cache_age_histogram.map! { |x| {:age => histogram_date_ms - x[0]*1000,
           :cache => total_free_cache - x[1],
           :persisted => persisted_storage} }
     end