Databases & Data Storage
Cursor
Definition
A database cursor is a control structure that enables traversal over the records in a database. Cursors facilitate subsequent processing in conjunction with the traversal, such as retrieval, addition and removal of database records.
Why It Matters
Cursors allow an application to process a large result set one row at a time, instead of loading the entire result into memory at once. This is essential for working with datasets that are too large to fit in RAM.
Contextual Example
A program needs to process a table with a billion rows. Instead of trying to load all billion rows into memory (which would crash the program), it opens a cursor on the query. It then fetches and processes the rows in small batches of 1000 at a time.
Common Misunderstandings
- While powerful, cursors can be inefficient and hold locks for a long time if not used carefully.
- In many modern programming languages, the database driver handles cursor creation implicitly when you iterate over a result set.