(maint) Optimize the status api using redis pipeline

Before this change looping over many pools would query the redis backend
for each pool, leading in slow response from the backend for configurations
with many pools (60+)
Changed the requests to use redis pipelines https://redis.io/topics/pipelining
This is supported since the beginning, so will not force any redis update for
users. The pipeline method runs the queries in batches and we need to loop
over the result and reduces the number of requests to redis by N=number of
pools in the configuration.

lib/vmpooler/api/helpers.rb

@@ -151,6 +151,53 @@ module Vmpooler
         backend.hvals("vmpooler__#{task}__" + date_str).map(&:to_f)
       end
 
+      # Takes the pools and a key to run scard on
+      # returns an integer for the total count
+      def get_total_across_pools_redis_scard(pools, key, backend)
+        # using pipelined is much faster than querying each of the pools and adding them
+        # as we get the result.
+        res = backend.pipelined do
+          pools.each do |pool|
+            backend.scard(key + pool['name'])
+          end
+        end
+        res.inject(0){ |m, x| m+x }.to_i
+      end
+
+      # Takes the pools and a key to run scard on
+      # returns a hash with each pool name as key and the value being the count as integer
+      def get_list_across_pools_redis_scard(pools, key, backend)
+        # using pipelined is much faster than querying each of the pools and adding them
+        # as we get the result.
+        temp_hash = {}
+        res = backend.pipelined do
+          pools.each do |pool|
+            backend.scard(key + pool['name'])
+          end
+        end
+        pools.each_with_index do |pool, i|
+          temp_hash[pool['name']] = res[i].to_i
+        end
+        temp_hash
+      end
+
+      # Takes the pools and a key to run hget on
+      # returns a hash with each pool name as key and the value as string
+      def get_list_across_pools_redis_hget(pools, key, backend)
+        # using pipelined is much faster than querying each of the pools and adding them
+        # as we get the result.
+        temp_hash = {}
+        res = backend.pipelined do
+          pools.each do |pool|
+            backend.hget(key, pool['name'])
+          end
+        end
+        pools.each_with_index do |pool, i|
+          temp_hash[pool['name']] = res[i].to_s
+        end
+        temp_hash
+      end
+
       def get_capacity_metrics(pools, backend)
         capacity = {
             current: 0,
@@ -159,12 +206,11 @@ module Vmpooler
         }
 
         pools.each do |pool|
-          pool['capacity'] = backend.scard('vmpooler__ready__' + pool['name']).to_i
-
-          capacity[:current] += pool['capacity']
           capacity[:total]   += pool['size'].to_i
         end
 
+        capacity[:current] = get_total_across_pools_redis_scard(pools, 'vmpooler__ready__', backend)
+
         if capacity[:total] > 0
           capacity[:percent] = ((capacity[:current].to_f / capacity[:total].to_f) * 100.0).round(1)
         end
@@ -183,12 +229,10 @@ module Vmpooler
             total:     0
         }
 
-        pools.each do |pool|
-          queue[:pending]   += backend.scard('vmpooler__pending__' + pool['name']).to_i
-          queue[:ready]     += backend.scard('vmpooler__ready__' + pool['name']).to_i
-          queue[:running]   += backend.scard('vmpooler__running__' + pool['name']).to_i
-          queue[:completed] += backend.scard('vmpooler__completed__' + pool['name']).to_i
-        end
+        queue[:pending]   = get_total_across_pools_redis_scard(pools,'vmpooler__pending__', backend)
+        queue[:ready]     = get_total_across_pools_redis_scard(pools, 'vmpooler__ready__', backend)
+        queue[:running]   = get_total_across_pools_redis_scard(pools, 'vmpooler__running__', backend)
+        queue[:completed] = get_total_across_pools_redis_scard(pools, 'vmpooler__completed__', backend)
 
         queue[:cloning] = backend.get('vmpooler__tasks__clone').to_i
         queue[:booting] = queue[:pending].to_i - queue[:cloning].to_i