Add new index to techinsights

This improved query for latest facts from several seconds to milliseconds on our instance

Signed-off-by: Tomasz Szuba <tszuba@box.com>

.changeset/grumpy-bikes-begin.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-tech-insights-backend': patch
+---
+
+Add DB index to improve latency of latest fact query

plugins/tech-insights-backend/knexfile.js

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2023 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.
+ */
+
+// This file makes it possible to run "yarn knex migrate:make some_file_name"
+// to assist in making new migrations
+module.exports = {
+  client: 'better-sqlite3',
+  connection: ':memory:',
+  useNullAsDefault: true,
+  migrations: {
+    directory: './migrations',
+  },
+};

plugins/tech-insights-backend/migrations/20230213170839_latest-facts-index.js

@@ -0,0 +1,36 @@
+/*
+ * Copyright 2023 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.
+ */
+
+const indexName = 'fact_id_entity_timestamp_idx';
+/**
+ * @param { import("knex").Knex } knex
+ * @returns { Promise<void> }
+ */
+exports.up = async knex => {
+  await knex.schema.alterTable('facts', table => {
+    table.index(['id', 'entity', 'timestamp'], indexName);
+  });
+};
+
+/**
+ * @param { import("knex").Knex } knex
+ * @returns { Promise<void> }
+ */
+exports.down = async knex => {
+  await knex.schema.alterTable('facts', table => {
+    table.dropIndex(indexName);
+  });
+};