Add entity type metrics

Signed-off-by: Johan Haals <johan.haals@gmail.com>

plugins/catalog-backend/src/next/DefaultCatalogProcessingEngine.ts

@@ -34,7 +34,7 @@ import {
   EntityProviderConnection,
   EntityProviderMutation,
 } from './types';
-import { Counter, Histogram, Summary } from 'prom-client';
+import { Counter, Summary } from 'prom-client';
 
 class Connection implements EntityProviderConnection {
   readonly validateEntityEnvelope = entityEnvelopeSchemaValidator();

plugins/catalog-backend/src/next/database/DefaultProcessingDatabase.ts

@@ -24,6 +24,7 @@ import type { Logger } from 'winston';
 import { Transaction } from '../../database';
 import { DeferredEntity } from '../processing/types';
 import { RefreshIntervalFunction } from '../refresh';
+import { initDatabaseMetrics } from './metrics';
 import {
   DbRefreshStateReferencesRow,
   DbRefreshStateRow,
@@ -51,7 +52,9 @@ export class DefaultProcessingDatabase implements ProcessingDatabase {
       logger: Logger;
       refreshInterval: RefreshIntervalFunction;
     },
-  ) {}
+  ) {
+    initDatabaseMetrics(options.database);
+  }
 
   async updateProcessedEntity(
     txOpaque: Transaction,

plugins/catalog-backend/src/next/database/metrics.ts

@@ -0,0 +1,68 @@
+/*
+ * Copyright 2021 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { Knex } from 'knex';
+import { Gauge } from 'prom-client';
+import { DbLocationsRow } from '../../database/types';
+import { DbRefreshStateRow, DbRelationsRow } from './tables';
+
+export function initDatabaseMetrics(knex: Knex) {
+  const seen = new Set<string>();
+  return {
+    entities_count: new Gauge({
+      name: 'catalog_entities_count',
+      help: 'Total amount of entities in the catalog',
+      labelNames: ['kind'],
+      async collect() {
+        const result = await knex<DbRefreshStateRow>('refresh_state').select(
+          'entity_ref',
+        );
+        const results = result
+          .map(row => row.entity_ref.split(':')[0])
+          .reduce((acc, e) => acc.set(e, (acc.get(e) || 0) + 1), new Map());
+
+        results.forEach((value, key) => {
+          seen.add(key);
+          this.set({ kind: key }, value);
+        });
+
+        // Set all the entities that were not seen to 0 and delete them from the seen set.
+        seen.forEach(key => {
+          if (!results.has(key)) {
+            this.set({ kind: key }, 0);
+            seen.delete(key);
+          }
+        });
+      },
+    }),
+    registered_locations: new Gauge({
+      name: 'catalog_registered_locations_count',
+      help: 'Total amount of registered locations in the catalog',
+      async collect() {
+        const total = await knex<DbLocationsRow>('locations').count();
+        this.set(total[0]['count(*)'] as number);
+      },
+    }),
+    relations: new Gauge({
+      name: 'catalog_relations_count',
+      help: 'Total amount of relations between entities',
+      async collect() {
+        const total = await knex<DbRelationsRow>('relations').count();
+        this.set(total[0]['count(*)'] as number);
+      },
+    }),
+  };
+}