Function flush_region 

pub(crate) async fn flush_region(
    mailbox: &MailboxRef,
    server_addr: &str,
    region_ids: &[RegionId],
    datanode: &Peer,
    timeout: Duration,
    error_strategy: ErrorStrategy,
) -> Result<()>

Flushes the regions on the datanode.

Retry Or Ignore:

• PusherNotFound, The datanode is unreachable.
• Failed to flush region on the Datanode.

Abort:

• MailboxTimeout, Timeout.
• UnexpectedInstructionReply.
• ExceededDeadline
• Invalid JSON.