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Memory-mapped IO used for temp files even though memory-mapped I/O is not used
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Chronological Hierarchical 
Hi,

Investigating this further, a potential fix is for the temp DBs to follow the main DB's MMap setting like so:
```
    i64 max = db->szMmap;
```

Similar to how the cache size for temp DBs follows the main DB's cache size in `sqlite3VdbeSorterInit`:
```
    mxCache = db->aDb[0].pSchema->cache_size;
```

This limits the total temp DB memory usage to a multiple of the setting for the main DB, as the settings apply to _every_ temp DB and we may need multiple ones for a query.