distributed-database – Tarik Billa

What is semi-join in database?

April 9, 2023 by Tarik

Simple example. Let’s select students with grades using left outer join: SELECT DISTINCT s.id FROM students s LEFT JOIN grades g ON g.student_id = s.id WHERE g.student_id IS NOT NULL Now the same with left semi-join: SELECT s.id FROM students s WHERE EXISTS (SELECT 1 FROM grades g WHERE g.student_id = s.id) The latter is … Read more

What scalability problems have you encountered using a NoSQL data store? [closed]

October 19, 2022 by Tarik

My current project actually. Storing 18,000 objects in a normalised structure: 90,000 rows across 8 different tables. Took 1 minute to retrieve and map them to our Java object model, that’s with everything correctly indexed etc. Storing them as key/value pairs using a lightweight text representation: 1 table, 18,000 rows, 3 seconds to retrieve them … Read more