docs(spanner): Update client side metrics and permission issues in README (#13491)

sakthivelmanii · gemini-code-assist[bot] · web-flow · commit ab56892e7bc1 · 2025-12-17T14:51:51.000+05:30
Co-authored-by: gemini-code-assist[bot] &lt;176961590+gemini-code-assist[bot]@users.noreply.github.com&gt;
diff --git a/spanner/README.md b/spanner/README.md
@@ -113,4 +113,27 @@ defer client.Close()
 // Example Log message for when transaction is recycled
 // session <session-info> checked out of pool at <session-checkout-time> is long running and will be removed due to possible session leak for goroutine 
 // <Stack Trace of transaction>
-```
+```
+
+## Metrics
+
+Cloud Spanner client supports [client-side metrics](https://cloud.google.com/spanner/docs/view-manage-client-side-metrics) that you can use along with server-side metrics to optimize performance and troubleshoot performance issues if they occur.
+
+Client-side metrics are measured from the time a request leaves your application to the time your application receives the response.
+In contrast, server-side metrics are measured from the time Spanner receives a request until the last byte of data is sent to the client.
+
+These metrics are enabled by default. You can opt out of using client-side metrics with the following code:
+
+```go
+client, err := spanner.NewClientWithConfig(
+	ctx, database, spanner.ClientConfig{DisableNativeMetrics: true},
+)
+if err != nil {
+log.Fatal(err)
+}
+defer client.Close()
+```
+
+You can also disable these metrics by setting `SPANNER_DISABLE_BUILTIN_METRICS` to `true`.
+
+> Note: Exporting client-side metrics requires the `monitoring.timeSeries.create` IAM permission. To grant this, ask your administrator to assign the [Monitoring Metric Writer](https://cloud.google.com/iam/docs/roles-permissions/monitoring#monitoring.metricWriter) (`roles/monitoring.metricWriter`) IAM role to your application's service account.
