new doc section on slow queries and SQL comments
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@ -653,20 +653,16 @@ It might return a single `Book`.
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[source,java]
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----
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interface Queries {
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@HQL("from Book where isbn = :isbn")
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Book findBookByIsbn(String isbn);
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}
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----
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It might even return `TypedQuery` or `SelectionQuery`:
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[source,java]
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----
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interface Queries {
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@HQL("from Book where title like :title")
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SelectionQuery<Book> findBooksByTitle(String title);
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}
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----
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This is extremely useful at times, since it allows the client to further manipulate the query:
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@ -675,9 +671,12 @@ This is extremely useful at times, since it allows the client to further manipul
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----
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List<Book> books =
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Queries_.findBooksByTitle(entityManager, titlePattern)
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.ascending(Book_.title) // order the results
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.setMaxResults(RESULTS_PER_PAGE) // return at most 20 results
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.setFirstResult(page*RESULTS_PER_PAGE) // start from the given page of results
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.setOrder(Order.asc(Book_.title)) // order the results
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.setPage(Page.page(RESULTS_PER_PAGE, page)) // return the given page of results
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.setFlushMode(FlushModeType.COMMIT) // don't flush session before query execution
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.setReadOnly(true) // load the entities in read-only mode
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.setCacheStoreMode(CacheStoreMode.BYPASS) // don't cache the results
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.setComment("Hello world!") // add a comment to the generated SQL
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.getResultList();
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----
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@ -980,6 +980,28 @@ long publisherCacheMissCount =
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Hibernate's statistics enable observability.
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Both {micrometer}[Micrometer] and {smallrye-metrics}[SmallRye Metrics] are capable of exposing these metrics.
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[[slow-queries]]
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=== Tracking down slow queries
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When a poorly-performing SQL query is discovered in production, it can sometimes be hard to track down exactly where in the Java code the query originates.
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Hibernate offers two configuration properties that can make it easier to identify a slow query and find its source.
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.Settings for tracking slow queries
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[%breakable,cols="25,~,~"]
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|===
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| Configuration property name | Purpose | Property value
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| `hibernate.log_slow_query` | Log slow queries at the `INFO` level | The minimum execution time, in milliseconds, which characterizes a "slow" query
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| `hibernate.use_sql_comments` | Prepend comments to the executed SQL | `true` or `false`
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|===
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When `hibernate.use_sql_comments` is enabled, the text of the HQL query is prepended as a comment to the generated SQL, which usually makes it easy to find the HQL in the Java code.
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The comment text may be customized:
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- by calling `Query.setComment(comment)` or `Query.setHint(AvailableHints.HINT_COMMENT,comment)`, or
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- via the `@NamedQuery` annotation.
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[[hibernate-reactive]]
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=== Reactive programming with Hibernate
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