Optimize clusters platforms batch queries

What does this MR do?

Optimizes the clusters_platforms counter queries for batch counting in usage data

Part of issue #208923 (closed)

Query

SELECT COUNT(“clusters”.“id”) FROM “clusters” INNER JOIN “cluster_providers_aws” ON “cluster_providers_aws”.“cluster_id” = “clusters”.“id” WHERE “clusters”.“provider_type” = 1 AND (“cluster_providers_aws”.“status” IN (3)) AND “clusters”.“enabled” = true AND “clusters”.“id” BETWEEN 0 AND 99999

Optimization

CREATE INDEX index_clusters_on_enabled_and_provider_type_and_id ON public.clusters USING btree (enabled, provider_type, id);
-- The query has been executed. Duration: 56.000 ms

Before: Bad! https://explain.depesz.com/s/eY1g

After: Good! https://explain.depesz.com/s/DnmU

Timing

After the index for batch counting takes 1 second pessimistic

• 33k clusters,
• with 10_000 batch sizes
• 33k/10_000 = 4 loops
• Time: < 1s ( cold cache with no time constraint )

Migration output

VERBOSE=true bundle exec rake db:migrate:up VERSION=20200310123229
== 20200310123229 AddIndexOnEnabledAndProviderTypeAndIdToClusters: migrating ==
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:clusters, [:enabled, :provider_type, :id], {:algorithm=>:concurrently})
   -> 0.0029s
-- execute("SET statement_timeout TO 0")
   -> 0.0007s
-- add_index(:clusters, [:enabled, :provider_type, :id], {:algorithm=>:concurrently})
   -> 0.0060s
-- execute("RESET ALL")
   -> 0.0006s
== 20200310123229 AddIndexOnEnabledAndProviderTypeAndIdToClusters: migrated (0.0103s) 

VERBOSE=true bundle exec rake db:migrate:down VERSION=20200310123229
== 20200310123229 AddIndexOnEnabledAndProviderTypeAndIdToClusters: reverting ==
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:clusters, [:enabled, :provider_type, :id], {:algorithm=>:concurrently})
   -> 0.0027s
-- execute("SET statement_timeout TO 0")
   -> 0.0004s
-- remove_index(:clusters, {:algorithm=>:concurrently, :column=>[:enabled, :provider_type, :id]})
   -> 0.0042s
-- execute("RESET ALL")
   -> 0.0004s
== 20200310123229 AddIndexOnEnabledAndProviderTypeAndIdToClusters: reverted (0.0079s)