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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
`@@ -1207,13 +1207,13 @@ acquire_sample_rows(Relation onerel, int elevel,`
`1207`	`1207`	`* The first targrows sample rows are simply copied into the`
`1208`	`1208`	`* reservoir. Then we start replacing tuples in the sample`
`1209`	`1209`	`* until we reach the end of the relation. This algorithm is`
`1210`		`- * from Jeff Vitter's paper (see full citationbelow). It`
`1211`		`- * works by repeatedly computing the number of tuples to skip`
`1212`		`- *before selecting a tuple, which replaces a randomly chosen`
`1213`		`- *element of the reservoir (current set oftuples). At all`
`1214`		`- *times the reservoir is a true random sample ofthetuples`
`1215`		`- * we've passed over so far, so when we fall off the end of`
`1216`		`- * the relation we're done.`
	`1210`	`+ * from Jeff Vitter's paper (see full citationin`
	`1211`	`+ *utils/misc/sampling.c). Itworks by repeatedly computing`
	`1212`	`+ *the number of tuples to skip before selecting a tuple,`
	`1213`	`+ *which replaces a randomly chosen element ofthe reservoir`
	`1214`	`+ *(current set of tuples). At all timesthereservoir is a`
	`1215`	`+ *true random sample of the tupleswe've passed over so far,`
	`1216`	`+ *so when we fall off the end ofthe relation we're done.`
`1217`	`1217`	`*/`
`1218`	`1218`	`if (numrows<targrows)`
`1219`	`1219`	`rows[numrows++]=heap_copytuple(&targtuple);`

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