XIDTAG ???

Why both
   int           pid;   TransactionId xid;

are used in XIDTAG?

lock.c:*                                      normal lock     user lock**      lockmethod                      1
      2*      tag.relId                       rel oid         0
^^^^^^^^^^^^^^^^^
Due to this, user-lock LOCKTAG is always different from
normal-lock tag and so XIDTAG.lock is different also.
*      tag.ItemPointerData.ip_blkid    block id        lock id2*      tag.ItemPointerData.ip_posid    tuple offset
lockid1*      xid.pid                         0               backend pid*      xid.xid                         xid or
0       0
 

Why not get rid of XIDTAG.xid and use XIDTAG.pid equal
to backend pid for both lock methods?

Comments?

Vadim