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hibernate-demo/docs/03-inserting-objects.md

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03 — Inserting objects efficiently

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Backs ankurm.com: Inserting objects efficiently.

Sources: InsertIdentityRunner / InsertSequenceRunner, entities WidgetIdentity / WidgetSequence. Run both with ./scripts/run.sh insert-identity and ./scripts/run.sh insert-sequence. Transcripts: docs/output/insert-identity.txt, docs/output/insert-sequence.txt.

The one-line difference that matters

Both entities persist 30 rows in a single transaction with identical settings:

hibernate.jdbc.batch_size: 25
hibernate.order_inserts: true

WidgetIdentity uses @GeneratedValue(strategy = GenerationType.IDENTITY). WidgetSequence uses @GeneratedValue(strategy = GenerationType.SEQUENCE) with a matching allocationSize = 25. That's the entire diff between the two entity classes.

What Hibernate's own statistics say happened

entityInsertCount prepareStatementCount
WidgetIdentity (IDENTITY) 30 30
WidgetSequence (SEQUENCE) 30 4

hibernate.jdbc.batch_size=25 did nothing at all for the IDENTITY run — every one of the 30 inserts is its own round trip to the database (prepareStatementCount equals entityInsertCount). With SEQUENCE, Hibernate knows the id before the row is written, so it can queue inserts and batch them: 30 rows at a batch size of 25 means two insert batches (25 + 5), plus two calls to pull the next block of ids from widget_seq (the sequence's allocationSize is also 25, so the first 25 ids come from one call and the remaining 5 force a second) — four prepared statements total, for the same 30 rows.

What surprised me building this

The number that surprised me was not "IDENTITY doesn't batch" — that's documented, if you know to look for it. It was seeing prepareStatementCount for SEQUENCE land at exactly 4, not 2. It's obvious in hindsight — allocationSize governs how often the sequence itself gets hit, independently of batch_size governing how the inserts get grouped — but "obvious in hindsight" and "what I would have guessed beforehand" are different things, and the gap between them is exactly what running this instead of describing it catches. If allocationSize had been left at JPA's default of 50 instead of matching batch_size at 25, the sequence would only need one call for all 30 ids, and prepareStatementCount would drop to 3 — a change to a number that has nothing to do with batching, moving a number that looks like it's entirely about batching.

The practical version of this: if a switch to SEQUENCE doesn't produce the batching win the Hibernate docs promise, checking hibernate.generate_statistics=true and reading prepareStatementCount directly answers "is it actually batching" in a way that reading the hibernate.jdbc.batch_size value in a config file cannot — the config says what was requested, not what happened.

Long-tail edge cases not covered above

  • save() vs persist() — save() is Hibernate's own pre-JPA API and still works, but returns the generated id immediately rather than void, and can be called outside a transaction (where it will fail later, confusingly, at flush time). persist() is the JPA-portable choice; there's no scenario for this in this repo because the observable difference is in the method signature and portability, not in captured runtime behaviour.
  • Bulk inserts via StatelessSession — bypasses the persistence context and lifecycle callbacks entirely; worth a dedicated repository of its own rather than a profile bolted onto this one, since the interesting failure modes (cascades silently not firing, no dirty checking) need a scenario built around triggering them specifically.
  • Native SQL batch inserts via createNativeQuery + addBatch — sidesteps Hibernate's own batching machinery altogether; the batching behaviour at that point is entirely the JDBC driver's, not Hibernate's, which is a different post.

Full captured transcripts

insert-identity.txt

Hibernate: create global temporary table HTE_book(rn_ integer not null, id bigint, version bigint, author varchar(255), title varchar(255), primary key (rn_)) transactional
Hibernate: create global temporary table HTE_widget_sequence(rn_ integer not null, id bigint, name varchar(255), primary key (rn_)) transactional
Hibernate: create table book (id bigint not null, author varchar(255), title varchar(255), version bigint not null, primary key (id))
Hibernate: create table widget_identity (id bigint generated by default as identity, name varchar(255), primary key (id))
Hibernate: create table widget_sequence (id bigint not null, name varchar(255), primary key (id))
Hibernate: create sequence book_seq start with 1 increment by 50
Hibernate: create sequence widget_seq start with 1 increment by 25
--- inserting 30 WidgetIdentity rows (GenerationType.IDENTITY) ---
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-1]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-2]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-3]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-4]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-5]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-6]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-7]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-8]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-9]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-10]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-11]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-12]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-13]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-14]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-15]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-16]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-17]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-18]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-19]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-20]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-21]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-22]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-23]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-24]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-25]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-26]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-27]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-28]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-29]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetIdentity */insert into widget_identity (name,id) values (?,default)
binding parameter (1:VARCHAR) <- [identity-30]
entityInsertCount     = 30
prepareStatementCount = 30
(with IDENTITY, expect prepareStatementCount to land close to entityInsertCount -- each insert has to go to the database immediately to hand back the generated key, so there is nothing left for hibernate.jdbc.batch_size to batch)

insert-sequence.txt

Hibernate: create global temporary table HTE_book(rn_ integer not null, id bigint, version bigint, author varchar(255), title varchar(255), primary key (rn_)) transactional
Hibernate: create global temporary table HTE_widget_sequence(rn_ integer not null, id bigint, name varchar(255), primary key (rn_)) transactional
Hibernate: create table book (id bigint not null, author varchar(255), title varchar(255), version bigint not null, primary key (id))
Hibernate: create table widget_identity (id bigint generated by default as identity, name varchar(255), primary key (id))
Hibernate: create table widget_sequence (id bigint not null, name varchar(255), primary key (id))
Hibernate: create sequence book_seq start with 1 increment by 50
Hibernate: create sequence widget_seq start with 1 increment by 25
--- inserting 30 WidgetSequence rows (GenerationType.SEQUENCE, allocationSize=25) ---
Hibernate: select next value for widget_seq
Hibernate: select next value for widget_seq
Hibernate: select next value for widget_seq
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-1]
binding parameter (2:BIGINT) <- [1]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-2]
binding parameter (2:BIGINT) <- [2]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-3]
binding parameter (2:BIGINT) <- [3]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-4]
binding parameter (2:BIGINT) <- [4]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-5]
binding parameter (2:BIGINT) <- [5]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-6]
binding parameter (2:BIGINT) <- [6]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-7]
binding parameter (2:BIGINT) <- [7]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-8]
binding parameter (2:BIGINT) <- [8]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-9]
binding parameter (2:BIGINT) <- [9]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-10]
binding parameter (2:BIGINT) <- [10]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-11]
binding parameter (2:BIGINT) <- [11]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-12]
binding parameter (2:BIGINT) <- [12]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-13]
binding parameter (2:BIGINT) <- [13]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-14]
binding parameter (2:BIGINT) <- [14]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-15]
binding parameter (2:BIGINT) <- [15]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-16]
binding parameter (2:BIGINT) <- [16]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-17]
binding parameter (2:BIGINT) <- [17]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-18]
binding parameter (2:BIGINT) <- [18]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-19]
binding parameter (2:BIGINT) <- [19]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-20]
binding parameter (2:BIGINT) <- [20]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-21]
binding parameter (2:BIGINT) <- [21]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-22]
binding parameter (2:BIGINT) <- [22]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-23]
binding parameter (2:BIGINT) <- [23]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-24]
binding parameter (2:BIGINT) <- [24]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-25]
binding parameter (2:BIGINT) <- [25]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-26]
binding parameter (2:BIGINT) <- [26]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-27]
binding parameter (2:BIGINT) <- [27]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-28]
binding parameter (2:BIGINT) <- [28]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-29]
binding parameter (2:BIGINT) <- [29]
Hibernate: /* insert for com.ankurm.hibernatedemo.model.WidgetSequence */insert into widget_sequence (name,id) values (?,?)
binding parameter (1:VARCHAR) <- [sequence-30]
binding parameter (2:BIGINT) <- [30]
entityInsertCount     = 30
prepareStatementCount = 4
(with SEQUENCE, the id is known before the row is written, so Hibernate can defer and batch the inserts -- expect prepareStatementCount well below entityInsertCount)

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