Hibernate pooled and pooled-lo identifier generators
Introduction In this post, we’ll uncover a sequence identifier generator combining identifier assignment efficiency and interoperability with other external systems (concurrently accessing the underlying database system). Traditionally there have been two sequence identifier strategies to choose from: sequence and seqhilo. The sequence identifier, always hitting the database for every new value assignment. Even with database sequence preallocation, we have a significant database round-trip cost. The seqhilo identifier, using the hilo algorithm. This generator calculates some identifier values in-memory, therefore reducing the database round-trip calls. The problem with this optimization technique is that… Read More
A beginner’s guide to Hibernate enhanced identifier generators
JPA identifier generators JPA defines the following identifier strategies: Strategy Description AUTO The persistence provider picks the most appropriate identifier strategy supported by the underlying database IDENTITY Identifiers are assigned by a database IDENTITY column SEQUENCE The persistence provider uses a database sequence for generating identifiers TABLE The persistence provider uses a separate database table to emulate a sequence object In my previous post I exampled the pros and cons of all these surrogate identifier strategies.
How do Identity, Sequence, and Table (sequence-like) generators work in JPA and Hibernate
Introduction In my previous post I talked about different database identifier strategies. This post will compare the most common surrogate primary key strategies: IDENTITY SEQUENCE TABLE (SEQUENCE) IDENTITY The IDENTITY type (included in the SQL:2003 standard) is supported by: Oracle 12c SQL Server MySQL (AUTO_INCREMENT) HSQLDB The IDENTITY generator allows an integer/bigint column to be auto-incremented on demand. The increment process happens outside of the current running transaction, so a roll-back may end-up discarding already assigned values (value gaps may happen). The increment process is very efficient since it uses a database… Read More
Hibernate and UUID identifiers
Introduction In this article, we are going to see how the UUID entity attributes are persisted when using JPA and Hibernate, for both assigned and auto-generated identifiers. In my previous post I talked about UUID surrogate keys and the use cases when there are more appropriate than the more common auto-incrementing identifiers. A UUID database type There are several ways to represent a 128-bit UUID, and whenever in doubt I like to resort to Stack Exchange for an expert advice. Because table identifiers are usually indexed, the more compact the database type… Read More
The hi/lo algorithm
Introduction In my previous post I talked about various database identifier strategies, you need to be aware of when designing the database model. We concluded that database sequences are very convenient because they are both flexible and efficient for most use cases. But even with cached sequences, the application requires a database round-trip for every new the sequence value. If your applications demand a high number of insert operations per transaction, the sequence allocation may be optimized with a hi/lo algorithm. The hi/lo algorithm The hi/lo algorithms split the sequences domain into… Read More
A beginner’s guide to natural and surrogate database keys
Types of primary keys All database tables must have one primary key column. The primary key uniquely identifies a row within a table therefore it’s bound by the following constraints: UNIQUE NOT NULL IMMUTABLE When choosing a primary key we must take into consideration the following aspects: the primary key may be used for joining other tables through a foreign key relationship the primary key usually has an associated default index, so the more compact the data type the less space the index will take the primary key assignment must ensure uniqueness… Read More
The minimal configuration for testing Hibernate
Introduction In my previous post I announced my intention of creating a personal Hibernate course. The first thing to start with is a minimal testing configuration. You only need Hibernate In a real production environment you won’t use Hibernate alone, as you may integrate it in a Java EE or Spring container. For testing Hibernate features you don’t need a full-blown framework stack, you can simply rely on Hibernate flexible configuration options.
How to detect the Hibernate N+1 query problem during testing
Introduction In this article, you are going to learn how to automatically detect the N+1 query problem when using JPA and Hibernate using the Hypersistence Utils open-source project. With Hibernate, you manage entity state transitions, which are then translated to SQL statements. The number of generated SQL statements is affected by the current fetching strategy, Criteria queries, or Collection mappings, and you might not always get what you expected. Ignoring SQL statements is risky, and it may eventually put a heavy toll on the overall application performance. I’m a strong advocate of… Read More
JPA Criteria API can generate unexpected SQL statements
Introduction In this article, we are going to learn why you should always check the SQL statements generated by JPA Criteria API queries when using Hibernate. Criteria API is very useful for dynamically building queries, but that’s the only use case where I’d use it. Whenever you have a UI with N filters that may arrive in any M combinations, it makes sense to have an API to construct queries dynamically since concatenating strings is always a path I’m running away from. The question is, are you aware of the SQL queries… Read More
