Every article tagged Indexes, in one place.
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Indexes are the single biggest lever for query performance. The right one turns a full table scan into a lookup of a few pages; the wrong ones slow down every write for nothing. B-tree: the default CREATE INDEX orders_customer_idx ON orders (customer_id); Work...
Most slow MySQL queries are missing an index or can't use the one that exists. EXPLAIN shows you which. Find slow queries SET GLOBAL slow_query_log = 'ON'; SET GLOBAL long_query_time = 0.5; -- seconds Or query performance_schema.events_statements_summary_by_di...
Without an index, MongoDB scans every document in a collection ( COLLSCAN ). Indexes make queries fast, and compound index order matters as much as in SQL. Creating indexes await orders.createIndex({ customerId: 1 }); await orders.createIndex({ status: 1, crea...
Short answer: an index is a separate, sorted data structure (usually a B-tree) that maps column values to row locations, so the database can find matching rows without scanning the whole table, much like a book's index. CREATE INDEX idx_orders_customer ON orde...
