fix: clarify connection pool document (#2877)

Author: GaoleMeng

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/JsonStreamWriter.java

@@ -312,8 +312,21 @@ public Builder setReconnectAfter10M(boolean reconnectAfter10M) {
  }
 
  /**
- * Enable multiplexing for this writer. In multiplexing mode tables will share the same
- * connection if possible until the connection is overwhelmed.
+ * Enables a static shared bidi-streaming connection pool that would dynamically scale up
+ * connections based on backlog within each individual connection. A single table's traffic
+ * might be splitted into multiple connections if needed. Different tables' traffic can also be
+ * multiplexed within the same connection.
+ *
+ * <pre>
+ * Each connection pool would have a upper limit (default to 20) and lower limit (default to
+ * 2) for the number of active connections. This parameter can be tuned via a static method
+ * exposed on {@link ConnectionWorkerPool}.
+ *
+ * Example:
+ * ConnectionWorkerPool.setOptions(
+ * Settings.builder().setMinConnectionsPerRegion(4).setMaxConnectionsPerRegion(10).build());
+ *
+ * </pre>
  *
  * @param enableConnectionPool
  * @return Builder

google-cloud-bigquerystorage/src/main/java/com/google/cloud/bigquery/storage/v1/StreamWriter.java

@@ -729,8 +729,21 @@ public Builder setEndpoint(String endpoint) {
  }
 
  /**
- * Enable multiplexing for this writer. In multiplexing mode tables will share the same
- * connection if possible until the connection is overwhelmed.
+ * Enables a static shared bidi-streaming connection pool that would dynamically scale up
+ * connections based on backlog within each individual connection. A single table's traffic
+ * might be splitted into multiple connections if needed. Different tables' traffic can also be
+ * multiplexed within the same connection.
+ *
+ * <pre>
+ * Each connection pool would have a upper limit (default to 20) and lower limit (default to
+ * 2) for the number of active connections. This parameter can be tuned via a static method
+ * exposed on {@link ConnectionWorkerPool}.
+ *
+ * Example:
+ * ConnectionWorkerPool.setOptions(
+ * Settings.builder().setMinConnectionsPerRegion(4).setMaxConnectionsPerRegion(10).build());
+ *
+ * </pre>
  *
  * @param enableConnectionPool
  * @return Builder