A beginner’s guide to flush strategies in JPA and Hibernate
Introduction In my previous post I introduced the entity state transitions Object-relational mapping paradigm. All managed entity state transitions are translated to associated database statements when the current Persistence Context gets flushed. Hibernate’s flush behavior is not always as obvious as one might think. Write-behind Hibernate tries to defer the Persistence Context flushing up until the last possible moment. This strategy has been traditionally known as transactional write-behind. The write-behind is more related to Hibernate flushing rather than any logical or physical transaction. During a transaction, the flush may occur multiple times…. Read More
A beginner’s guide to entity state transitions with JPA and Hibernate
Introduction Hibernate shifts the developer mindset from SQL statements to entity state transitions. Once an entity is actively managed by Hibernate, all changes are going to be automatically propagated to the database. Manipulating domain model entities (along with their associations) is much easier than writing and maintaining SQL statements. Without an ORM tool, adding a new column requires modifying all associated INSERT ir UPDATE statements. But Hibernate is no silver bullet either. Hibernate doesn’t free us from ever worrying about the actual executed SQL statements. Controlling Hibernate is not as straightforward as… Read More
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) DB2 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… 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.
