client: Reimplement persistent transaction code using TRANS3_COMMIT
Implementing persistent trasnaction code from Samba.
Persistent transaction code was reimplemented in Samba using g_lock.tdb
to hold transaction locks and using TRANS3_COMMIT control.
Implementation details:
1. When starting a transaction, create a record with "transaction-<dbid>"
as key and store current server_id in the structure.
2. If a record already exists, some other client has already started a
transaction. Verify that the process corresponding to server_id stored
in the record really exists or it's a stale record and overwrite it.
3. All modifications to the actual persistent database are stored in a
marshal buffer.
4. When transaction is committed, read the sequence number of the
persistent database and increment it. Sequence number record is also
stored in the marshal buffer.
5. Send the changed records (marshal buffer) in TRANS3_COMMIT control
to all the active nodes.
6. If all controls succeed, verify that the sequence number has been
incremented. Commit is successful. If any of the controls fail,
abort the transaction.
7. In case sequence number has not yet been incremented, then database
recovery has been triggered. So repeat from step 5.
Signed-off-by: Amitay Isaacs <amitay@gmail.com>