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JPA and Hibernate Data Layer Intern
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Our email events table holds a few hundred million rows and grows by around two million a day, which makes careless Hibernate mappings extremely visible.
Where you come in
You will join the data layer group and spend six months living between Java and MySQL. Concretely: hunting the N+1 queries our reporting screens trigger, converting EAGER associations to explicit fetch joins and entity graphs, designing composite indexes and then proving with EXPLAIN that they earned their disk space, and building DTO projections so a dashboard stops hydrating full entities just to render one number.
The half of this job that is not code
You will learn to measure before you change anything. Every optimisation you propose arrives with a before number and an after number, taken the same way, and you present both in the fortnightly performance review. That habit is the real deliverable of this internship.
Background we expect
No prior job experience, and we mean that. We do expect you have written SQL by hand, know what a foreign key is for, and have used an ORM enough to have been surprised by one at least once. Final-year students and recent graduates are equally welcome to apply.
Responsibilities
- Profile reporting endpoints and identify the N+1 query patterns sitting behind them
- Replace EAGER associations with explicit fetch joins and entity graphs
- Design composite indexes and validate them with EXPLAIN before and after
- Build DTO projections so dashboards stop hydrating full entities for a single figure
- Add regression tests that fail if a fixed query starts issuing extra selects again
- Present before and after measurements in the fortnightly performance review
Requirements
- Final-year student or recent graduate with no prior industry experience
- Hand-written SQL including joins, grouping and an understanding of foreign keys
- Some ORM exposure in any language, plus curiosity about the SQL it generates
- Java fundamentals strong enough to read someone else's entity classes
Skills
Benefits
- Stipend paid monthly across all six months
- Direct mentorship from the engineer who owns our database schema
- Genuine ownership of performance work with numbers attached to your name
- Remote-first working with travel covered for a quarterly team meetup