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Correct obsolete UNION hash aggs comment. 

Oversight in commit 1f39bce0, which added disk-based hash aggregation.

Backpatch: 13-, where disk-based hash aggregation was introduced.
This commit is contained in:
Peter Geoghegan 2020-07-28 17:14:07 -07:00
parent f36e82072c
commit b1d79127ed
1 changed files with 4 additions and 5 deletions
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9
src/backend/optimizer/prep/prepunion.c
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@ -944,11 +944,10 @@ make_union_unique(SetOperationStmt *op, Path *path, List *tlist,
/*
* XXX for the moment, take the number of distinct groups as equal to the
* total input size, ie, the worst case. This is too conservative, but we
* don't want to risk having the hashtable overrun memory; also, it's not
* clear how to get a decent estimate of the true size. One should note
* as well the propensity of novices to write UNION rather than UNION ALL
* even when they don't expect any duplicates...
* total input size, ie, the worst case. This is too conservative, but
* it's not clear how to get a decent estimate of the true size. One
* should note as well the propensity of novices to write UNION rather
* than UNION ALL even when they don't expect any duplicates...
*/
dNumGroups = path->rows;