Batch Inserts Via EntityManager (MySQL)

Description: This application is a sample of batching inserts via EntityManager in MySQL. This way you can easily control the flush() and clear() cycles of the Persistence Context (1st Level Cache) inside the current transaction. This is not possible via Spring Boot, saveAll(Iterable<S> entities), since this method executes a single flush per transaction. Another advantage is that you can call persist() instead of merge() - this is used behind the scene by the SpringBoot saveAll(Iterable<S> entities) and save(S entity).

If you want to execute a batch per transaction (recommended) then check this example.

Key points:

• in application.properties set spring.jpa.properties.hibernate.jdbc.batch_size
• in application.properties set spring.jpa.properties.hibernate.generate_statistics (just to check that batching is working)
• in application.properties set JDBC URL with rewriteBatchedStatements=true (optimization for MySQL)
• in application.properties set JDBC URL with cachePrepStmts=true (enable caching and is useful if you decide to set prepStmtCacheSize, prepStmtCacheSqlLimit, etc as well; without this setting the cache is disabled)
• in application.properties set JDBC URL with useServerPrepStmts=true (this way you switch to server-side prepared statements (may lead to signnificant performance boost))
• in case of using a parent-child relationship with cascade persist (e.g. one-to-many, many-to-many) then consider to set up spring.jpa.properties.hibernate.order_inserts=true to optimize the batching by ordering inserts
• in entity, use the assigned generator since MySQL IDENTITY will cause insert batching to be disabled
• in your DAO layer, flush and clear the Persistence Context from time to time (e.g. for each batch); this way you avoid to "overwhelm" the Persistence Context
• if is not needed, then ensure that Second Level Cache is disabled via spring.jpa.properties.hibernate.cache.use_second_level_cache=false

Output example:

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