Remove unused Prometheus recording rules from `synapse-v2.rules` and add...

Remove unused Prometheus recording rules from `synapse-v2.rules` and add comments describing where the rest are used. (#13756)

changelog.d/13756.misc

+Remove unused Prometheus recording rules from `synapse-v2.rules` and add comments describing where the rest are used.
\ No newline at end of file

contrib/prometheus/synapse-v2.rules

 groups:
 - name: synapse
   rules:
-  - record: "synapse_federation_transaction_queue_pendingEdus:total"
-    expr: "sum(synapse_federation_transaction_queue_pendingEdus or absent(synapse_federation_transaction_queue_pendingEdus)*0)"
-  - record: "synapse_federation_transaction_queue_pendingPdus:total"
-    expr:   "sum(synapse_federation_transaction_queue_pendingPdus or absent(synapse_federation_transaction_queue_pendingPdus)*0)"
-  - record: 'synapse_http_server_request_count:method'
-    labels:
-      servlet: ""
-    expr: "sum(synapse_http_server_request_count) by (method)"
-  - record: 'synapse_http_server_request_count:servlet'
-    labels:
-      method: ""
-    expr: 'sum(synapse_http_server_request_count) by (servlet)'
-
-  - record: 'synapse_http_server_request_count:total'
-    labels:
-      servlet: ""
-    expr: 'sum(synapse_http_server_request_count:by_method) by (servlet)'
-
-  - record: 'synapse_cache:hit_ratio_5m'
-    expr: 'rate(synapse_util_caches_cache_hits[5m]) / rate(synapse_util_caches_cache[5m])'
-  - record: 'synapse_cache:hit_ratio_30s'
-    expr: 'rate(synapse_util_caches_cache_hits[30s]) / rate(synapse_util_caches_cache[30s])'
-
+  # These 3 rules are used in the included Prometheus console
   - record: 'synapse_federation_client_sent'
     labels:
       type: "EDU"
@@ -37,6 +15,7 @@ groups:
       type: "Query"
     expr: 'sum(synapse_federation_client_sent_queries) by (job)'
 
+  # These 3 rules are used in the included Prometheus console
   - record: 'synapse_federation_server_received'
     labels:
       type: "EDU"
@@ -50,6 +29,7 @@ groups:
       type: "Query"
     expr: 'sum(synapse_federation_server_received_queries) by (job)'
 
+  # These 2 rules are used in the included Prometheus console
   - record: 'synapse_federation_transaction_queue_pending'
     labels:
       type: "EDU"
@@ -59,6 +39,7 @@ groups:
       type: "PDU"
     expr: 'synapse_federation_transaction_queue_pending_pdus + 0'
 
+  # These 3 rules are used in the included Grafana dashboard
   - record: synapse_storage_events_persisted_by_source_type
     expr: sum without(type, origin_type, origin_entity) (synapse_storage_events_persisted_events_sep_total{origin_type="remote"})
     labels:
@@ -71,8 +52,12 @@ groups:
     expr: sum without(type, origin_type, origin_entity) (synapse_storage_events_persisted_events_sep_total{origin_entity!="*client*",origin_type="local"})
     labels:
       type: bridges
+
+  # This rule is used in the included Grafana dashboard
   - record: synapse_storage_events_persisted_by_event_type
     expr: sum without(origin_entity, origin_type) (synapse_storage_events_persisted_events_sep_total)
+
+  # This rule is used in the included Grafana dashboard
   - record: synapse_storage_events_persisted_by_origin
     expr: sum without(type) (synapse_storage_events_persisted_events_sep_total)