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Remove "fuzzy comparison" logic in qsort comparison function for

choose_bitmap_and(). It was way too fuzzy --- per comment, it was meant to be1% relative difference, but was actually coded as 0.01 absolute difference,thus causing selectivities of say 0.001 and 0.000000000001 to be treated asequal. I believe this thinko explains Maxim Boguk's recent complaint. Whilewe could change it to a relative test coded like compare_fuzzy_path_costs(),there's a bigger problem here, which is that any fuzziness at all renders thecomparison function non-transitive, which could confuse qsort() to the pointof delivering completely wrong results. So forget the whole thing and justdo an exact comparison.

1 parentca9d503 commitae0c8d0Copy full SHA for ae0c8d0

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-8

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src/backend/optimizer/path
- indxpath.c

1 file changed

-8

lines changed

`‎src/backend/optimizer/path/indxpath.c`

Lines changed: 6 additions & 8 deletions

Original file line number	Diff line number	Diff line change
`@@ -9,7 +9,7 @@`
`9`	`9`	`*`
`10`	`10`	`*`
`11`	`11`	`* IDENTIFICATION`
`12`		`- * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.207 2006/06/06 17:59:57 tgl Exp $`
	`12`	`+ * $PostgreSQL: pgsql/src/backend/optimizer/path/indxpath.c,v 1.208 2006/06/07 17:08:07 tgl Exp $`
`13`	`13`	`*`
`14`	`14`	`*-------------------------------------------------------------------------`
`15`	`15`	`*/`
`@@ -674,20 +674,18 @@ bitmap_path_comparator(const void a, const void b)`
`674`	`674`	`Costbcost;`
`675`	`675`	`Selectivityaselec;`
`676`	`676`	`Selectivitybselec;`
`677`		`-Selectivitydiff;`
`678`	`677`
`679`	`678`	`cost_bitmap_tree_node(pa,&acost,&aselec);`
`680`	`679`	`cost_bitmap_tree_node(pb,&bcost,&bselec);`
`681`	`680`
`682`	`681`	`/*`
`683`		`- *Since selectivities areoften pretty crude, don't put blind faith`
`684`		`- *in them; if the selectivities are within 1% of being the same, treat`
`685`		`- *them as equal and sort by cost instead.`
	`682`	`+ *If selectivities arethe same, sort by cost. (Note: there used to be`
	`683`	`+ *logic here to do "fuzzy comparison", but that's a bad idea because it`
	`684`	`+ *fails to be transitive, which will confuse qsort terribly.)`
`686`	`685`	`*/`
`687`		`-diff=aselec-bselec;`
`688`		`-if (diff<-0.01)`
	`686`	`+if (aselec<bselec)`
`689`	`687`	`return-1;`
`690`		`-if (diff>0.01)`
	`688`	`+if (aselec>bselec)`
`691`	`689`	`return1;`
`692`	`690`
`693`	`691`	`if (acost<bcost)`

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`‎src/backend/optimizer/path/indxpath.c`

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