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some more documentation about lock modes 

Signed-off-by: Gavin King <gavin@hibernate.org>
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Gavin King 2024-05-14 13:59:43 +02:00
parent 8c3b68cd78
commit 43a8851d51
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documentation/src/main/asciidoc/introduction/Tuning.adoc
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@ -943,8 +943,20 @@ an entity is written to the database using
| `PESSIMISTIC_WRITE` | A pessimistic `for update` lock
| `PESSIMISTIC_FORCE_INCREMENT` | A pessimistic lock enforced using an immediate
`update` to increment the version
| `NONE` | No lock; assigned when an entity is read from the second-level cache
|===
Note that an `OPTIMISTIC` lock is always verified at the end of the transaction, even when the entity has not been modified.
This is slightly different to what most people mean when they talk about an "optimistic lock".
It's never necessary to request an `OPTIMISTIC` lock on a modified entity, since the version number is always verified when a SQL `update` is executed.
[CAUTION]
====
JPA has its own `LockModeType`, which enumerates most of the same modes.
However, JPA's `LockModeType.READ` is a synonym for `OPTIMISTIC` -- it's not the same as Hibernate's `LockMode.READ`.
Similarly, `LockModeType.WRITE` is a synonym for `OPTIMISTIC_FORCE_INCREMENT` and is not the same as `LockMode.WRITE`.
====
[[statistics]]
=== Collecting statistics