NotificationsYou must be signed in to change notification settings
Fork6
Star31

Commitae0c8d0

committed

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

File tree

1 file changed

-8

lines changed

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)`

0 commit comments

Comments

(0)

Movatterモバイル変換

Navigation Menu

Search code, repositories, users, issues, pull requests...

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Commitae0c8d0

File tree

1 file changed

1 file changed

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

0 commit comments