How can you identify and resolve database deadlocks?

1 What causes database deadlocks?

Database deadlocks are usually caused by one of the following factors: concurrency, isolation, locking, and transaction design. Concurrency refers to the number of transactions that are executed simultaneously on the database. The higher the concurrency, the higher the chance of conflicts and deadlocks. Isolation refers to the level of visibility and consistency that each transaction has over the data. The higher the isolation, the more locks are acquired and held by each transaction, which can also increase the risk of deadlocks. Locking refers to the mechanism that the database uses to ensure that only one transaction can modify a resource at a time. Locking can be done at different levels, such as table, page, row, or key. The lower the level, the more granular and efficient the locking, but also the more complex and prone to deadlocks. Transaction design refers to the way that the application code interacts with the database. Poor transaction design can lead to unnecessary or excessive locking, long-running transactions, or inconsistent locking order, which can all contribute to deadlocks.

2 How to detect database deadlocks?

Database deadlocks can be detected by using various methods, such as monitoring, logging, tracing, or profiling. Monitoring refers to observing the performance and health of the database system using tools such as dashboards, alerts, or reports. Monitoring can help you identify potential or existing deadlocks by looking at metrics such as lock waits, lock timeouts, lock escalations, or deadlock victims. Logging refers to recording the events and errors that occur on the database system using tools such as error logs, event logs, or audit logs. Logging can help you capture the details and context of each deadlock occurrence, such as the time, duration, session, query, error code, or message. Tracing refers to capturing the execution path and behavior of each transaction using tools such as trace flags, extended events, or performance schema. Tracing can help you analyze the root cause and sequence of each deadlock scenario, such as the resources, locks, owners, waiters, or cycles involved. Profiling refers to measuring the performance and resource consumption of each transaction using tools such as query plans, execution statistics, or performance monitors. Profiling can help you optimize and tune each transaction to reduce the likelihood and impact of deadlocks.

4 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?