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Update reference to sampling algorithm in analyze.c

Commit83e176e moved row sampling functions from analyze.c toutils/misc/sampling.c, but failed to update comment referring tothe sampling algorithm from Jeff Vitter's paper. Correct thecomment by pointing to utils/misc/sampling.c.Author: Etsuro FujitaDiscussion:https://postgr.es/m/CAPmGK154gp%2BQd%3DcorQOv%2BPmbyVyZBjp_%2Bhb766UJeD1e_ie6XQ%40mail.gmail.com

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Original file line number	Diff line number	Diff line change
`@@ -1048,13 +1048,13 @@ acquire_sample_rows(Relation onerel, int elevel,`
`1048`	`1048`	`* The first targrows sample rows are simply copied into the`
`1049`	`1049`	`* reservoir. Then we start replacing tuples in the sample until`
`1050`	`1050`	`* we reach the end of the relation. This algorithm is from Jeff`
`1051`		`- * Vitter's paper (see full citationbelow). It works by`
`1052`		`- * repeatedly computing the number of tuples to skip before`
`1053`		`- * selecting a tuple, which replaces a randomly chosen element of`
`1054`		`- * the reservoir (current set of tuples). At all times the`
`1055`		`- * reservoir is a true random sample of the tuples we've passed`
`1056`		`- * over so far, so when we fall off the end of the relation we're`
`1057`		`- * done.`
	`1051`	`+ * Vitter's paper (see full citationin utils/misc/sampling.c). It`
	`1052`	`+ *works byrepeatedly computing the number of tuples to skip`
	`1053`	`+ *beforeselecting a tuple, which replaces a randomly chosen`
	`1054`	`+ *element ofthe reservoir (current set of tuples). At all times`
	`1055`	`+ *thereservoir is a true random sample of the tuples we've`
	`1056`	`+ *passedover so far, so when we fall off the end of the relation`
	`1057`	`+ *we'redone.`
`1058`	`1058`	`*/`
`1059`	`1059`	`if (numrows<targrows)`
`1060`	`1060`	`rows[numrows++]=ExecCopySlotHeapTuple(slot);`

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