Resolving deadlock when multiple stored procedures are reading and updating the same table in SQL Server 2014 database

Question

I have two stored procedures. First SP runs when records are received from server to save it in relationship table. Second SP runs after every fixed interval of time through a scheduler from .NET server.

First Stored Procedure Code:

BEGIN TRY
INSERT INTO RELATIONSHIP SELECT DATA FROM ANOTHER TABLE
SELECT INTO TEMPTABLE FROM RELATIONSHIP
UPDATE RELATIONSHIP SET...
END TRY

Second Stored Procedure Code:

BEGIN TRY
BEGIN TRANSACTION
SELECT INTO TEMPTABLE FROM RELATIONSHIP
UPDATE RELATIONSHIP SET ISPROCESSED = 1 WHERE ...
COMMIT TRANSACTION
END TRY

When the second stored procedure runs, it runs into a deadlock. Also, The first stored procedure is not written within a transaction.

What would be the best practice here to resolve the deadlock considering the code logic and flow cannot be changed? I have written code related to relationship table only and skipped code related to other table, as deadlock is occurring on this table. Let me know if you need more information, I can post the deadlock logs too from health monitor.

    <deadlock>
 <victim-list>
  <victimProcess id="process207c2cd3c28" />
 </victim-list>
 <process-list>
  <process id="process207c2cd3c28" taskpriority="0" logused="0" waitresource="PAGE: 5:1:53898 " waittime="774" ownerId="10078305" transactionname="UPDATE" lasttranstarted="2021-07-27T15:43:22.120" XDES="0x20d350857d0" lockMode="U" schedulerid="10" kpid="9288" status="suspended" spid="74" sbid="0" ecid="16" priority="0" trancount="0" lastbatchstarted="2021-07-27T15:43:21.030" lastbatchcompleted="2021-07-27T15:43:21.030" lastattention="1900-01-01T00:00:00.030" clientapp=".Net SqlClient Data Provider" hostname="" hostpid="6900" isolationlevel="read committed (2)" xactid="10078305" currentdb="5" currentdbname="" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056">
   <executionStack>
    <frame procname="ProcessMessage" line="153" stmtstart="11462" stmtend="11928" sqlhandle="0x03000500abb08931c097be0072ad000001000000000000000000000000000000000000000000000000000000">
UPDATE lar
        SET 
            -- some code
        FROM Relationship lar INNER JOIN --few joins   </frame>
    <frame procname="" line="133" stmtstart="10056" stmtend="10112" sqlhandle="0x03000500caf178474f6b59006ead000001000000000000000000000000000000000000000000000000000000">
    </frame>
   </executionStack>
   <inputbuf>
Proc [Database Id = 5 Object Id = 1199108554]   </inputbuf>
  </process>
  <process id="process20958d27848" taskpriority="0" logused="2060" waitresource="PAGE: 5:1:53794 " waittime="523" ownerId="9400887" transactionname="ProcessDiscrepancies" lasttranstarted="2021-07-27T13:24:45.573" XDES="0x20d2cb80420" lockMode="IU" schedulerid="2" kpid="7576" status="suspended" spid="94" sbid="0" ecid="0" priority="0" trancount="2" lastbatchstarted="2021-07-27T13:24:45.570" lastbatchcompleted="2021-07-27T13:24:45.573" lastattention="1900-01-01T00:00:00.573" clientapp=".Net SqlClient Data Provider" hostname="" hostpid="6900" loginname="" isolationlevel="read committed (2)" xactid="9400887" currentdb="5" currentdbname="" lockTimeout="4294967295" clientoption1="673185824" clientoption2="128056">
   <executionStack>
    <frame procname="ProcessDiscrepancies" line="140" stmtstart="10254" stmtend="11002" sqlhandle="0x030005003968a12f1d68be0072ad000001000000000000000000000000000000000000000000000000000000">
UPDATE lar

            SET 

                IsProcessed = 1,

            FROM Relationship lar   

            INNER JOIN --few joins  </frame>
    <frame procname="adhoc" line="1" stmtend="60" sqlhandle="0x010005007715562a80688d2c0d02000000000000000000000000000000000000000000000000000000000000">
EXEC ProcessDiscrepancie    </frame>
   </executionStack>
   <inputbuf>
EXEC ProcessDiscrepancies   </inputbuf>
  </process>
 </process-list>
 <resource-list>
  <pagelock fileid="1" pageid="53898" dbid="5" subresource="FULL" objectname="Relationship" id="lock1ffa075f280" mode="IU" associatedObjectId="72057597189357568">
   <owner-list>
    <owner id="process20958d27848" mode="IU" />
   </owner-list>
   <waiter-list>
    <waiter id="process207c2cd3c28" mode="U" requestType="wait" />
   </waiter-list>
  </pagelock>
  <pagelock fileid="1" pageid="53794" dbid="5" subresource="FULL" objectname="Relationship" id="lock204c8f59680" mode="U" associatedObjectId="72057597189357568">
   <owner-list>
    <owner id="process207c2cd3c28" mode="U" />
   </owner-list>
   <waiter-list>
    <waiter id="process20958d27848" mode="IU" requestType="wait" />
   </waiter-list>
  </pagelock>
 </resource-list>
</deadlock>

Answer 1

Few suggestions for fixing the deadlock scenario. You have to try and see, if they help in fixing the issues.

1. Always handle the transactions in similar way. Have a pattern to follow for transactions. Below is the template, I am following. Reference SO Post

CREATE PROCEDURE [Name]
AS
SET XACT_ABORT, NOCOUNT ON

DECLARE @starttrancount int

BEGIN TRY
    SELECT @starttrancount = @@TRANCOUNT

    IF @starttrancount = 0
        BEGIN TRANSACTION

       [...Perform work, call nested procedures...]

    IF @starttrancount = 0 
        COMMIT TRANSACTION
END TRY
BEGIN CATCH
    IF XACT_STATE() <> 0 AND @starttrancount = 0 
        ROLLBACK TRANSACTION;
    THROW;
    --before SQL Server 2012 use 
    --RAISERROR [rethrow caught error using @ErrorNumber, @ErrorMessage, etc]
END CATCH
GO

2. Make transactions as small as possible. Why are you loading the temptable inside the transaction. Try to load it outside the transaction to make the transaction smaller.

3. Define proper indexes to make the queries to run faster, it will make the transactions smaller

4. Why are you INSERT and UPDATE Relationship table one by one. Why can't you to take care of your UPDATE as part of your INSERT. It will totally avoid the UPDATE statement.