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expand doc section on pessimistic locking #10180

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21 changes: 19 additions & 2 deletions documentation/src/main/asciidoc/introduction/Tuning.adoc
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Expand Up @@ -998,8 +998,14 @@ Indeed, the usual practice is to avoid having transactions that span user intera
That said, there _is_ also a place for pessimistic locks, which can sometimes reduce the probability of transaction rollbacks.

Therefore, the `find()`, `lock()`, and `refresh()` methods of the session accept an optional link:{doc-javadoc-url}/org/hibernate/LockMode.html[`LockMode`].
We can also specify a `LockMode` for a query.
The lock mode can be used to request a pessimistic lock, or to customize the behavior of optimistic locking:
Here's the simplest way to execute a `select ... for update` in Hibernate:

[source,java]
Book book = session.find(Book.class, isbn, LockMode.PESSIMISTIC_WRITE);

We can also link:{doc-javadoc-url}/org/hibernate/query/SelectionQuery.html#setLockMode(jakarta.persistence.LockModeType)[specify] a `LockMode` for a query.

A lock mode can be used to request a pessimistic lock, or to customize the behavior of optimistic locking:

.Optimistic and pessimistic lock modes
[%breakable,cols="26,~"]
Expand Down Expand Up @@ -1037,6 +1043,17 @@ However, JPA's `LockModeType.READ` is a synonym for `OPTIMISTIC` -- it's not the
Similarly, `LockModeType.WRITE` is a synonym for `OPTIMISTIC_FORCE_INCREMENT` and is not the same as `LockMode.WRITE`.
====

A pessimistic lock request may be combined with an explicit `Timeout`.

[source,java]
session.lock(book, LockMode.PESSIMISTIC_WRITE, Timeout.seconds(2))

The interface link:{doc-javadoc-url}/org/hibernate/Timeouts.html[`Timeouts`] defines some special instances of `Timeout` which may be used to request use of link:{doc-javadoc-url}/org/hibernate/Timeouts.html#NO_WAIT[`for update nowait`] or link:{doc-javadoc-url}/org/hibernate/Timeouts.html#SKIP_LOCKED[`for update skip locked`] on databases which support these options.

[source,java]
session.lock(book, LockMode.PESSIMISTIC_WRITE, Timeouts.NO_WAIT)


[[statistics]]
=== Collecting statistics

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