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Update reference to sampling algorithm in analyze.c

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Commit 83e176ec1 moved row sampling functions from analyze.c to
utils/misc/sampling.c, but failed to update comment referring to
the sampling algorithm from Jeff Vitter's paper. Correct the
comment by pointing to utils/misc/sampling.c.

Author: Etsuro Fujita
Discussion: https://postgr.es/m/CAPmGK154gp%2BQd%3DcorQOv%2BPmbyVyZBjp_%2Bhb766UJeD1e_ie6XQ%40mail.gmail.com
This commit is contained in:
Tomas Vondra 2019-06-27 18:14:25 +02:00
parent 5329606693
commit 30e1b395c9
1 changed files with 7 additions and 7 deletions
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14
src/backend/commands/analyze.c
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@ -1152,13 +1152,13 @@ acquire_sample_rows(Relation onerel, int elevel,
* The first targrows sample rows are simply copied into the * The first targrows sample rows are simply copied into the
* reservoir. Then we start replacing tuples in the sample * reservoir. Then we start replacing tuples in the sample
* until we reach the end of the relation. This algorithm is * until we reach the end of the relation. This algorithm is
* from Jeff Vitter's paper (see full citation below). It * from Jeff Vitter's paper (see full citation in
* works by repeatedly computing the number of tuples to skip * utils/misc/sampling.c). It works by repeatedly computing
* before selecting a tuple, which replaces a randomly chosen * the number of tuples to skip before selecting a tuple,
* element of the reservoir (current set of tuples). At all * which replaces a randomly chosen element of the reservoir
* times the reservoir is a true random sample of the tuples * (current set of tuples). At all times the reservoir is a
* we've passed over so far, so when we fall off the end of * true random sample of the tuples we've passed over so far,
* the relation we're done. * so when we fall off the end of the relation we're done.
*/ */
if (numrows < targrows) if (numrows < targrows)
rows[numrows++] = heap_copytuple(&targtuple); rows[numrows++] = heap_copytuple(&targtuple);