> [!NOTE] Sort > <table> > <tr> > <td width="25%"><img src="assets/ex_sort.png"></td> > <td>A resource-intensive operation that orders the result set. If the dataset exceeds <code>work_mem</code>, the engine will spill the sort to disk (external merge sort), which is significantly slower due to I/O overhead. Often used as a precursor to Merge Joins or Unique operations.</td> > </tr> > </table> > > ```sql > -- Sorting the animals table by a non-indexed column > EXPLAIN (ANALYZE, COSTS, BUFFERS, VERBOSE) > SELECT * FROM animals ORDER BY created_at; > ``` > > ```text > Sort (cost=1776.77..1826.77 rows=20000 width=27) (actual time=2.721..3.401 rows=20000 loops=1) > Output: id, name, species_id, created_at > Sort Key: animals.created_at > Sort Method: quicksort Memory: 1862kB > Buffers: shared hit=151 > -> Seq Scan on public.animals (...) > ``` > > <table> > <tr> > <td rowspan="5" width="25%"><img src="assets/ex_sort.svg"></td> > <td><b>Performance</b></td><td>CPU and memory intensive; may spill to disk (external sort) if the dataset exceeds <code>work_mem</code>.</td> > </tr> > <tr><td><b>Factors</b></td><td>Dataset size, available <code>work_mem</code>, and the complexity of the sort key.</td></tr> > <tr><td><b>Cost</b></td><td><code>sorting cost * number of rows</code></td></tr> > <tr><td><b>Operates on</b></td><td><a href="Structures/Result Set">Result Set</a></td></tr> > <tr><td><b>Workloads</b></td><td><a href="Workloads/IO/BufFile/BufFileRead">IO: BufFileRead</a>, <a href="Workloads/IO/BufFile/BufFileWrite">IO: BufFileWrite</a>, <a href="Workloads/LWLock/Buffers/BufferContent">LWLock: BufferContent</a></td></tr> > <tr><td colspan="3"><b>Description</b>: Sorts rows.</td></tr> > </table>