NotificationsYou must be signed in to change notification settings
Fork6
Star31

Commit29cf61a

committed

Consider fillfactor when estimating relation size

When table_block_relation_estimate_size() estimated the number of tuplesin a relation without statistics (e.g. right after load), it did notconsider fillfactor when calculating density. With non-defaultfillfactor values, this may result in significant overestimate of thenumber of tuples - up to 10x with the minimum 10% fillfactor. This mayhave unexpected consequences, e.g. when creating hash indexes.This considers the current fillfactor value in the "no statistics" codepath. If the fillfactor changes after loading data into the table, theestimate may be off. But that seems much less likely than changing thefillfactor before the data load.Reviewed-by: Corey Huinker, Peter EisentrautDiscussion:https://postgr.es/m/cf154ef9-6bac-d268-b735-67a3443debba@enterprisedb.com

1 parent087a933 commit29cf61aCopy full SHA for 29cf61a

File tree

1 file changed

-1

lines changed

src/backend/access/table
- tableam.c

1 file changed

-1

lines changed

`‎src/backend/access/table/tableam.c`

Lines changed: 9 additions & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -737,11 +737,19 @@ table_block_relation_estimate_size(Relation rel, int32 *attr_widths,`
`737`	`737`	`* and (c) different table AMs might use different padding schemes.`
`738`	`738`	`*/`
`739`	`739`	`int32tuple_width;`
	`740`	`+intfillfactor;`
	`741`	`+`
	`742`	`+/*`
	`743`	`+ * Without reltuples/relpages, we also need to consider fillfactor.`
	`744`	`+ * The other branch considers it implicitly by calculating density`
	`745`	`+ * from actual relpages/reltuples statistics.`
	`746`	`+ */`
	`747`	`+fillfactor=RelationGetFillFactor(rel,HEAP_DEFAULT_FILLFACTOR);`
`740`	`748`
`741`	`749`	`tuple_width=get_rel_data_width(rel,attr_widths);`
`742`	`750`	`tuple_width+=overhead_bytes_per_tuple;`
`743`	`751`	`/* note: integer division is intentional here */`
`744`		`-density=usable_bytes_per_page /tuple_width;`
	`752`	`+density=(usable_bytes_per_page*fillfactor /100) /tuple_width;`
`745`	`753`	`}`
`746`	`754`	`tuples=rint(density (double)curpages);`
`747`	`755`

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!

Commit29cf61a

File tree

1 file changed

1 file changed

`‎src/backend/access/table/tableam.c`

0 commit comments