Glossary
Every term the courses use, defined in one line and then in a paragraph. Written to be read out of order.
Showing 5 of 5 matching “Index”
Work triggered by the clock.
A scheduled job: nightly cleanup, hourly reindex, the weekly digest. Named after a Unix utility from the 1970s. Fails silently by default, because nobody is waiting for it.
See also Scheduled job, Background job, UTC
Reading every row to answer one question.
What the database resorts to when no index supports your query. Instant with ten rows, catastrophic with ten million, which is why this problem never appears during development.
A lookup structure that makes one kind of query fast.
Like the index at the back of a book. Makes lookups on the indexed column fast, does nothing for other columns, costs storage, and slows down writes. Chosen per query pattern, not sprinkled everywhere.
See also Query, N+1, Full table scan
Answering a question that spans two tables.
Matching rows across tables using a key: orders with their customer names attached. Ordinary and fast when the columns involved are indexed, and very slow when they are not.
See also Foreign key, Index, Normalisation
A question asked of the database.
A request for data. Cheap when an index supports it, ruinous when it forces a scan of every row. Which questions you ask should be a design decision, not an accident.
See also Index, N+1, Full table scan