Data engineering·Cost, layout and query performance
the sort did not fit in memory, started writing to local disk, and the query went from forty seconds to nineteen minutes.
Spill to disk
Also calledspilling, out-of-memory spill, disk spill
An operator writing intermediate data to disk or to remote storage because it exceeded available memory. It is not an error, which is why it hides: the query still succeeds, just enormously slower. It is one of the first things to look for in a query that got dramatically worse without the SQL changing, and the usual causes are a data volume increase, a skewed key or a join order the planner got wrong.