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Fix ancient thinko in default table rowcount estimation.

The code used sizeof(ItemPointerData) where sizeof(ItemIdData) is correct,since we're trying to account for a tuple's line pointer. Spotted byTomonari Katsumata (bug #12584).Although this mistake is of very long standing, no back-patch, since it'sa relatively harmless error and changing it would risk changing defaultplanner behavior in stable branches. (I don't see any change in regressiontest outputs here, but the buildfarm may think differently.)

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src/backend/optimizer/util
- plancat.c

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`‎src/backend/optimizer/util/plancat.c`

Lines changed: 1 addition & 1 deletion

Original file line number	Diff line number	Diff line change
`@@ -509,7 +509,7 @@ estimate_rel_size(Relation rel, int32 *attr_widths,`
`509`	`509`
`510`	`510`	`tuple_width=get_rel_data_width(rel,attr_widths);`
`511`	`511`	`tuple_width+=sizeof(HeapTupleHeaderData);`
`512`		`-tuple_width+=sizeof(ItemPointerData);`
	`512`	`+tuple_width+=sizeof(ItemIdData);`
`513`	`513`	`/* note: integer division is intentional here */`
`514`	`514`	`density= (BLCKSZ-SizeOfPageHeaderData) /tuple_width;`
`515`	`515`	`}`

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Commit75df6dc

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`‎src/backend/optimizer/util/plancat.c`

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