hibernate-demo/locking

locking

Companion module for the ankurm.com article on optimistic vs pessimistic locking in Hibernate 7. Two threads, one in-memory H2 database, plain Hibernate (no Spring). Each test writes what it observed to output/.

Versions

Component	Version	Notes
Hibernate ORM	7.4.14.Final	latest 7.x GA on Maven Central on 2026-10-25 (8.0.0.Beta3 is also listed; it is not GA)
Jakarta Persistence	3.2.0
H2	2.4.240	in memory, OPTIMIZE_REUSE_RESULTS=0 (see Db.java)
JUnit Jupiter / AssertJ	6.0.3 / 3.27.7
Java	25 (Temurin 25.0.5+8)

This module has its own pom.xml and does not use the Spring Boot parent of the main hibernate-demo project. All locking behaviour here is H2's. SKIP LOCKED, NOWAIT and deadlock handling differ between databases, so check your own.

Run

./scripts/run-all.sh

Output

File	What it shows
01-lost-update.txt	two transactions read 100, both deposit, one deposit is lost (no @Version)
02-version-stops-it.txt	the same race with @Version: the second commit fails with OptimisticLockException
03-retry-loop.txt	six threads, thirty increments, retry on OptimisticLockException; the final balance is exact
04-pessimistic-write.txt	PESSIMISTIC_WRITE makes the second transaction wait; SQL uses for update
05-no-wait.txt	Timeouts.NO_WAIT fails at once (for update nowait)
06-skip-locked.txt	two workers claim different tickets (for update skip locked)
07-deadlock.txt	opposite lock order deadlocks; the same order for everyone does not