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Clamp adjusted ndistinct to positive integer in estimate_hash_bucketsize().

This avoids a possible divide-by-zero in the following calculation,and rounding the number to an integer seems like saner behavior anyway.Assuming IEEE math, the division would yield +Infinity which would getreplaced by 1.0 at the bottom of the function, so nothing reallyinteresting would ensue; but avoiding divide-by-zero seems like agood idea on general principles.Per report from Piotr Stefaniak. No back-patch since this seemsmostly cosmetic.

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src/backend/utils/adt
- selfuncs.c

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`‎src/backend/utils/adt/selfuncs.c`

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Original file line number	Diff line number	Diff line change
`@@ -3541,7 +3541,10 @@ estimate_hash_bucketsize(PlannerInfo root, Node hashkey, double nbuckets)`
`3541`	`3541`	`* selectivity of rel's restriction clauses that mention the target Var.`
`3542`	`3542`	`*/`
`3543`	`3543`	`if (vardata.rel)`
	`3544`	`+{`
`3544`	`3545`	`ndistinct *=vardata.rel->rows /vardata.rel->tuples;`
	`3546`	`+ndistinct=clamp_row_est(ndistinct);`
	`3547`	`+}`
`3545`	`3548`
`3546`	`3549`	`/*`
`3547`	`3550`	`* Initial estimate of bucketsize fraction is 1/nbuckets as long as the`

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Commitfa09f89

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`‎src/backend/utils/adt/selfuncs.c`

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