backend: pack next record LSN into the encoded message

This field only needs to be read after the batch is decoded,
so we can move into the body to get more efficient encoding.

Author: VladLazar

postgres-protocol/src/message/backend.rs

@@ -375,15 +375,10 @@ impl ReplicationMessage<Bytes> {
             INTERPRETED_WAL_RECORD_TAG => {
                 let streaming_lsn = buf.read_u64::<BigEndian>()?;
                 let commit_lsn = buf.read_u64::<BigEndian>()?;
-                let next_record_lsn = match buf.read_u64::<BigEndian>()? {
-                    0 => None,
-                    lsn => Some(lsn),
-                };
 
                 ReplicationMessage::RawInterpretedWalRecords(RawInterpretedWalRecordsBody {
                     streaming_lsn,
                     commit_lsn,
-                    next_record_lsn,
                     data: buf.read_all(),
                 })
             }
@@ -971,7 +966,6 @@ impl<D> XLogDataBody<D> {
 pub struct RawInterpretedWalRecordsBody<D> {
     streaming_lsn: u64,
     commit_lsn: u64,
-    next_record_lsn: Option<u64>,
     data: D,
 }
 
@@ -986,11 +980,6 @@ impl<D> RawInterpretedWalRecordsBody<D> {
         self.commit_lsn
     }
 
-    #[inline]
-    pub fn next_record_lsn(&self) -> Option<u64> {
-        self.next_record_lsn
-    }
-
     #[inline]
     pub fn data(&self) -> &D {
         &self.data