LOCK: V7 DX "Distributed TX"

Maclean Liu(刘相兵

Lock:           DX "Distributed TX"

How Many:
1 lock per process that tries to do a distributed transaction.

Who Uses:
RECO's & distributed sessions

When & How Used:

X mode:

  Used to ensure that only one process is using a distributed
                  transaction slot at a time.

S mode:

  When querying the underlying X$ table/s

  In particular XA uses:

SELECT k2gtifmt, k2gtitid_ext, k2gtibid

  FROM sys.v$xatrans$;

  for XA_RECOVER operations which will request locks in S

  mode to read the information from the table.

Id1, Id2 Combination:

Slot Number (of distributed transaction table), Always 0

Lock Value Block:
Not Used.
Scope:
Local Enqueue.
Deadlock Sensitive:
Yes.
Operation:
Synchronous.

Parameters:
<Parameter:DISTRIBUTED_TRANSACTIONS>

Related:
<View:X$K2GTE> shows the distributed transaction table

Bug 511309 hashing algorithm for the DX table is

     flawed. No noticable problem.

Acknowledgements:    Thanks to AKOLK.US for main info.