Once the  deadlock has occured , it will  remain in a constant deadlock state. The SQL server clean up routine comes along every few seconds and releases one of the victims (the one using the least amount of resources).An error message is returned – error mesaage 1205.
A deadlock is not the same as blocking. Blocking is a normal condition of database applications, although excessive blocking can create service degradation, and it is the aim of the DBA to identify excessive blocking. Blocking is not to be confused with deadlocking.

Lets look at the example below, which illustrates a deadlock scenario.

Assume there are 2 transaction running simultaneously.

Transaction 1 – holds a lock on “order number 1”
Transaction 2 – holds a lock on “vehichle 1”

The deadlock will occur if Transaction1 – requires a lock “vehicle 1 ” and Transaction2 – requires a lock on “order number 1”. In other words a  dependancy.

Analysis of how to resolve the deadlocking should include:

1)Consider the order of the transactions within the stored procedure.
2)You can see from the breakdown below , the potential scenario . i.e beacause this is one long running transaction , if multiple transactions are running , a few millisecond transactions would create a situation where deadlocks (not blocking would occur.)
3)Are so many steps required ?
4)Can BEGIN TRANS …COMMIT TRANS  be placed around more sub steps , to release locks?
5)A way must be found to release the (probably ) exclusive locks created by the UPDATE,DELETES,INSERTS, without upsetting the data integrity.Speak to the developers , and consider the implications of adjusting transaction management.
6)What is going on in usp_SESSORD_Order_WriteCLIENTOrderVehicle? Is this trying to access resources , which have exclusive locks from processes in the main body?
7)Can you control a queue from the app , that would queue this transaction?

BEGIN TRANSACTION 1
if exists CLIENT
UPDATE CLIENT
else
INSERT CLIENT
FROM sessordCLIENT

SELECT @custId = origCustId FROM sessord_CLIENTs WHERE sessionSessionId = @sessionId
UPDATE SESSORD_CLIENTs   SET origCustId = @@IDENTITY   WHERE sessionSessionId = @sessionId

end

IF exits – order sessorder

—booking ref
if exists …..
SELECT @bookedOrderId = o.orderId, @bookingImage = o.bookingImage + 1     FROM ORDERS o
INNER JOIN sessord_orders so ON o.BookingRef = so.BookingRef  WHERE so.sessionSessionId = @sessionId

–orderdetpax
if exists (SELECT…)
DELETE orderDetPax FROM orderDetPax odv  INNER JOIN orderDets od ON od.orderdetId = odv.paxdetorderdetId
LEFT JOIN sessord_orderDetPax sodv ON odv.PaxDetId = sodv.origPaxDetid
WHERE sodv.PaxDetId IS NULL AND od.orderdetOrderId = @bookedOrderId

–orderdetveh
if exists(SELECT)
DELETE orderDetVeh             FROM orderDetVeh odv               INNER JOIN orderDets od      ON od.orderdetId = odv.vehdetorderdetId
LEFT JOIN sessord_orderDetVeh sodv   ON odv.VehDetId = sodv.origOrderDetVehid
WHERE sodv.VehDetId IS NULL  AND od.orderdetOrderId = @bookedOrderId

–order det journey
DELETE …….

—order added value

DELETE …….
–ordersupred

DELETE  ……..

–orderDets

DELETE ……….

–orderpayments

DELETE ………..

–notetext
DELETE …………
–note
DELETE …………..
–OrderDets
UPDATE …………..

ELSE
INSERT ORDER ………..

END

INSERT INTO orderDetVeh from SESSORD_orderDetVeh
INSERT INTO orderDetPax from SESSORD_orderDetPax
INSERT INTO orderDetJourney FROM SESSORD_orderDetJourney
INSERT INTO orderAddedValue FROM SESSORD_orderAddedValue
INSERT INTO orderSupRed (SESSORD_orderSupRed
INSERT INTO dbo.orderPayments FROM [dbo].[sessord_orderpayments] sop
INSERT INTO dbo.Note from [sessord_note]
INSERT INTO Notetext from [SESSORD_NoteText]

if bookingImage > 0

UPDATE orders
UPDATE orderDetVeh

UPDATE orderDetPax
UPDATE OrderDetJourney
UPDATE orderAddedValue
UPDATE orderSupRed
UPDATE orderPayments
UPDATE dbo.note
UPDATE dbo.notetext

EXEC [usp_SESSORD_Order_WriteCLIENTOrderVehicle] @sessionId, @amendedBy

COMMIT TRANSACTION