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Consider index-only scans even when there is no matching qual or ORDER BY.

By popular demand.

1 parenta018546 commit600d320Copy full SHA for 600d320

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+12

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lines changed

src/backend/optimizer/path
- indxpath.c

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+12

-13

lines changed

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

Lines changed: 12 additions & 13 deletions

Original file line number	Diff line number	Diff line change
`@@ -317,8 +317,7 @@ find_usable_indexes(PlannerInfo root, RelOptInfo rel,`
`317`	`317`	`booluseful_predicate;`
`318`	`318`	`boolfound_clause;`
`319`	`319`	`boolindex_is_ordered;`
`320`		`-boolindex_only_scan= false;`
`321`		`-boolchecked_index_only= false;`
	`320`	`+boolindex_only_scan;`
`322`	`321`
`323`	`322`	`/*`
`324`	`323`	`* Check that index supports the desired scan type(s)`
`@@ -436,17 +435,20 @@ find_usable_indexes(PlannerInfo root, RelOptInfo rel,`
`436`	`435`	`}`
`437`	`436`
`438`	`437`	`/*`
`439`		`- * 3. Generate an indexscan path if there are relevant restriction`
	`438`	`+ * 3. Check if an index-only scan is possible.`
	`439`	`+ */`
	`440`	`+index_only_scan=check_index_only(rel,index);`
	`441`	`+`
	`442`	`+/*`
	`443`	`+ * 4. Generate an indexscan path if there are relevant restriction`
`440`	`444`	`* clauses in the current clauses, OR the index ordering is`
`441`	`445`	`* potentially useful for later merging or final output ordering, OR`
`442`		`- * the index has a predicate that was proven by the current clauses.`
	`446`	`+ * the index has a predicate that was proven by the current clauses,`
	`447`	`+ * OR an index-only scan is possible.`
`443`	`448`	`*/`
`444`		`-if (found_clause\|\|useful_pathkeys!=NIL\|\|useful_predicate)`
	`449`	`+if (found_clause\|\|useful_pathkeys!=NIL\|\|useful_predicate\|\|`
	`450`	`+index_only_scan)`
`445`	`451`	`{`
`446`		`-/* First, detect whether index-only scan is possible */`
`447`		`-index_only_scan=check_index_only(rel,index);`
`448`		`-checked_index_only= true;`
`449`		`-`
`450`	`452`	`ipath=create_index_path(root,index,`
`451`	`453`	`restrictclauses,`
`452`	`454`	`orderbyclauses,`
`@@ -460,7 +462,7 @@ find_usable_indexes(PlannerInfo root, RelOptInfo rel,`
`460`	`462`	`}`
`461`	`463`
`462`	`464`	`/*`
`463`		`- *4. If the index is ordered, a backwards scan might be interesting.`
	`465`	`+ *5. If the index is ordered, a backwards scan might be interesting.`
`464`	`466`	`* Again, this is only interesting at top level.`
`465`	`467`	`*/`
`466`	`468`	`if (index_is_ordered&&possibly_useful_pathkeys&&`
`@@ -472,9 +474,6 @@ find_usable_indexes(PlannerInfo root, RelOptInfo rel,`
`472`	`474`	`index_pathkeys);`
`473`	`475`	`if (useful_pathkeys!=NIL)`
`474`	`476`	`{`
`475`		`-if (!checked_index_only)`
`476`		`-index_only_scan=check_index_only(rel,index);`
`477`		`-`
`478`	`477`	`ipath=create_index_path(root,index,`
`479`	`478`	`restrictclauses,`
`480`	`479`	`NIL,`

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Commit600d320

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

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