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So far the hashtable stored representative tuples in the form of its input slot, with all columns in the hashtable that are not needed (i.e. not grouped upon or functionally dependent) set to NULL. Thats good for saving memory, but it turns out that having tuples full of NULL isn't free. slot_deform_tuple is faster if there's no NULL bitmap even if no NULLs are encountered, and skipping over leading NULLs isn't free. So compute a separate tuple descriptor that only contains the needed columns. As columns have already been moved in/out the slot for the hashtable that does not imply additional per-row overhead. Author: Andres Freund Reviewed-By: Heikki Linnakangas Discussion: https://postgr.es/m/20161103110721.h5i5t5saxfk5eeik@alap3.anarazel.de |
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| .. | ||
| bitmapset.h | ||
| execnodes.h | ||
| extensible.h | ||
| lockoptions.h | ||
| makefuncs.h | ||
| memnodes.h | ||
| nodeFuncs.h | ||
| nodes.h | ||
| params.h | ||
| parsenodes.h | ||
| pg_list.h | ||
| plannodes.h | ||
| primnodes.h | ||
| print.h | ||
| readfuncs.h | ||
| relation.h | ||
| replnodes.h | ||
| tidbitmap.h | ||
| value.h | ||