The best way to avoid deadlock in SQL Server is to enlist the help of a SQL deadlocks monitoring tool. You could also set the number of retries allowed to a set number, reducing the chances of an infinite loop. Application error handling: Using TRY.CATCH logic, you could trap for the deadlock number.Deadlock priority: By specifying a transaction’s priority to High, Normal (Default), or Low, you can enable current sessions to continue processing if there’s SQL Server deadlock.Avoid this by using COMMITTED SNAPSHOT or SNAPSHOT, in which a reader doesn’t take locks on objects and instead uses row versions for isolations. Transaction isolation levels: The default transaction isolation level on SQL Server, READ COMMITTED, can promote deadlocks between writers and readers of data.To avoid these deadlocks otherwise, make transactions as short as possible and keep access objects in the same logical order. Object order access: To create deadlocks for testing purposes, access database objects in a different order.Without a foreign key index, cascading actions will take longer and increase the chances of a deadlock. Foreign key indexes: Reduce SQL Server deadlock stemming from cascading referential integrity by creating indexes that match your foreign key columns.Covering indexes: By removing bookmark lookups entirely, a covering index can reduce your chances of deadlock caused by bookmark lookups.Here are some common ways to resolve SQL Server deadlock: As noted above, as soon as a deadlock is detected, SQL Server automatically chooses the “victim” and rolls back that transaction-then it’s up to you and your IT administrative team to resolve deadlocks in SQL Server. SQL Server is capable of automatic detection through a lock monitor. There are several ways to resolve SQL Server deadlock depending on the situation. Eventually, deadlocks could result in a complete halt to processing inside your database engine. Whenever a SQL Server lock on a table occurs, operations are delayed or even stopped entirely.
Poor database design, a lack of indexing, inappropriate isolation levels, and poorly written queries are some common causes of deadlock. When you get a SQL Server deadlock notification, you’ll find one transaction called the “victim” and one called the “survivor.” The victim is the session that gets rolled back, and it’s automatically selected by SQL Server based on deadlock priority and rollback cost. A SQL deadlock query cannot be completed until the lock is released, and neither can its fellow deadlocked SQL query. This happens when the transactions hold locks on resources the other transactions also need, resulting in a SQL Server lock on a table. Deadlocks in SQL Server occur when two or more transactions, or collections of SQL queries, block each other through a cyclical dependency.
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