Answer
MySQL sorts using in-memory temp tables when possible and switches to disk-based files if data exceeds memory limits.
Quick Answer
MySQL uses in-memory sort buffers (sort_buffer_size) for ORDER BY. If result fits in buffer: in-memory quicksort. If too large: uses temporary files on disk (filesort with external merge sort). EXPLAIN shows "Using filesort" when sorting can't use an index. Temporary tables: created in memory (tmp_table_size, max_heap_table_size limit) or spill to disk. Increase these limits or add indexes to avoid disk operations.
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SugharaIQ Editorial Team
Verified Answer
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Source: SugharaIQ