![[wl_client_clientwrite.png|256]] - **Description**: The backend process is waiting for the operating system to accept data being sent back to the client. This typically happens when the client is slow to consume results, causing the OS TCP send buffer to fill up, which ultimately blocks the backend's `send()` system call until the client ACKs the packets. - **Operations**: - [[CustomScanForeignScan]] - **Resources**: [[Network]], [[CPU]]