Merge branch 'smaller-prom-redis-keys' into 'master'

Reduce redis key size by half for Prometheus::ProxyService

See merge request gitlab-org/gitlab!20006

app/services/prometheus/proxy_service.rb

@@ -5,9 +5,17 @@ module Prometheus
     include ReactiveCaching
     include Gitlab::Utils::StrongMemoize
 
-    self.reactive_cache_key = ->(service) { service.cache_key }
+    self.reactive_cache_key = ->(service) { [] }
     self.reactive_cache_lease_timeout = 30.seconds
-    self.reactive_cache_refresh_interval = 30.seconds
+
+    # reactive_cache_refresh_interval should be set to a value higher than
+    # reactive_cache_lifetime.  If the refresh_interval is less than lifetime
+    # then the ReactiveCachingWorker will re-query prometheus for this
+    # PromQL query even though it's (probably) already been picked up by
+    # the frontend
+    # refresh_interval should be set less than lifetime only if this data
+    # is expected to change *and* be fetched again by the frontend
+    self.reactive_cache_refresh_interval = 90.seconds
     self.reactive_cache_lifetime = 1.minute
     self.reactive_cache_worker_finder = ->(_id, *args) { from_cache(*args) }
 

changelogs/unreleased/smaller-prom-redis-keys.yml

+---
+title: Reduce redis key size for the Prometheus proxy and the amount of queries by half
+merge_request: 20006
+author:
+type: performance

spec/services/prometheus/proxy_service_spec.rb

@@ -8,6 +8,12 @@ describe Prometheus::ProxyService do
   set(:project) { create(:project) }
   set(:environment) { create(:environment, project: project) }
 
+  describe 'configuration' do
+    it 'ReactiveCaching refresh is not needed' do
+      expect(described_class.reactive_cache_refresh_interval).to be > described_class.reactive_cache_lifetime
+    end
+  end
+
   describe '#initialize' do
     let(:params) { ActionController::Parameters.new(query: '1').permit! }