I have this SP to retrieve PK values from a table that has a row for each user table:

BEGIN TRANSACTION
-- Note the HOLDLOCK!
SELECT @cNext = NextId
  FROM IdTable (HOLDLOCK)
  WHERE Table = @tcTablename
IF (@@rowcount = 1)
  BEGIN
    -- get the next Pk
    UPDATE IdTable
      SET NextId = NextId + 1
      WHERE Table = @tcTablename
    COMMIT TRANSACTION
  END
ELSE
    SET @cNext = NULL
    ROLLBACK TRANSACTION
END

Intermittantly, no PK value is being assigned. I am wondering if this could be a problem with the HOLDLOCK? If another query runs this SP while the first one is in a transaction will the second one block or will it fall into the ELSE clause? Will an UPDATE lock fix it?

TIA