Java Deadlock Prevention Example: Understanding and Resolving Hanging Transactions

In distributed systems, transactions are an essential mechanism for ensuring data consistency and integrity. However, these transactions can sometimes lead to a situation known as deadlock, where multiple transactions wait indefinitely for each other to release resources. This article will explore the concept of deadlocks in Ignite, a popular in-memory computing platform, and discuss ways to prevent and resolve hanging transactions.

Identifying Deadlock

In Ignite, a deadlock occurs when two or more transactions lock keys within different orders. For instance, Transaction A locks key1 and then attempts to lock key2, while Transaction B locks key2 and then tries to lock key1. This can lead to a situation where both transactions are stuck waiting for each other to release the locked resources.

Web Console Features

To help developers identify and resolve deadlocks, Ignite provides several features in its Web Console. First, the console should allow users to rollback any transaction via the user interface (UI). Additionally, log records should contain information about near nodes, transaction IDs, cache names, and keys involved in the deadlock.

Ongoing Transactions List

The Web Console should also provide a screen that lists all ongoing transactions in the cluster. This list should include information such as the node on which the transaction is running, its ID, and the caches it is accessing. If a deadlock is detected, Ignite should report this to the logs.

Configuring Default Behavior

Developers should have the ability to configure the default behavior for handling deadlocks. The options could include REPORT_ONLY, ROLLBACK, or manual rollback of selected transactions through the Web Console or Visor.

Detection and Solution

To prevent deadlocks, each NEAR node in the cluster should periodically scan its list of local transactions and initiate a deadlock detection procedure when it finds a potential deadlock. This procedure should be similar to the one used for timed-out transactions.

Possible Deadlocks in Ignite

Ignite can detect deadlocked transactions, but only those with explicit timeouts or default timeouts set to a value greater than zero. There are several types of possible deadlocks that can occur in Ignite, including:

* Deadlocks involving multiple keys and transactions

* Deadlocks between optimistic serializable transactions

Each deadlock type should be accompanied by suggestions on how to resolve the issue with minimal impact on the running cluster.

In conclusion, understanding and preventing deadlocks is crucial for ensuring data consistency and integrity in distributed systems. Ignite's features and configuration options provide a robust solution for detecting and resolving hanging transactions, allowing developers to build reliable and scalable applications. By configuring default behavior and using the Web Console, developers can identify and resolve deadlocks effectively, minimizing downtime and data loss.

Java deadlock prevention example