Indexing

Your query is slow. You add an index. It gets faster. Magic, right? Not quite. Indexes are powerful but misunderstood. Used well, they turn seconds into milliseconds. Used poorly, they slow down writes, waste storage, and sometimes make queries slower. Let’s demystify them. What Is an Index? An index is a separate data structure that helps the database find rows without scanning the entire table. Think of it like a book’s index—instead of reading every page to find “PostgreSQL,” you look it up in the index and jump directly to page 247. ...

Every junior developer learns that indexes make queries fast. What they don’t learn is that indexes also make writes slow, consume disk space, and can actively hurt performance when misused. Let’s fix that. What Indexes Actually Do An index is a separate data structure that maintains a sorted copy of specific columns, with pointers back to the full rows. Think of it like the index in a book — instead of reading every page to find “PostgreSQL,” you flip to the index, find the entry, and jump directly to page 247. ...