docs: add example for consumed units logging in query service

Author: polRk

examples/query-service/consumed-units.ts

@@ -0,0 +1,37 @@
+process.env.YDB_SDK_PRETTY_LOGS = '1';
+
+import { Driver, getCredentialsFromEnv, Logger } from 'ydb-sdk';
+import { main } from '../utils';
+
+async function run(logger: Logger, endpoint: string, database: string) {
+    const authService = getCredentialsFromEnv();
+    logger.info('Driver initializing...');
+    const driver = new Driver({ endpoint, database, authService });
+    const timeout = 10000;
+    if (!await driver.ready(timeout)) {
+        logger.fatal(`Driver has not become ready in ${timeout}ms!`);
+        process.exit(1);
+    }
+
+    await driver.queryClient.do({
+        fn: async (session) => {
+            const res = await session.execute({ text: `SELECT 1;`, });
+
+            // Always drain the result to avoid session stuck
+            for await (const resultSet of res.resultSets) {
+                for await (const row of resultSet.rows) {
+                }
+            }
+        },
+        onTrailer: (trailer) => {
+            let consumedUnits = trailer.get('x-ydb-consumed-units')
+            if (consumedUnits) {
+                console.info(`Consumed units: ${consumedUnits}`);
+            }
+        }
+    });
+
+    await driver.destroy();
+}
+
+main(run);