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Use list_copy_head() instead of list_truncate(list_copy(...), ...)

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Truncating off the end of a freshly copied List is not a very efficient
way of copying the first N elements of a List.

In many of the cases that are updated here, the pattern was only being
used to remove the final element of a List.  That's about the best case
for it, but there were many instances where the truncate trimming the List
down much further.

4cc832f94 added list_copy_head(), so let's use it in cases where it's
useful.

Author: David Rowley
Discussion: https://postgr.es/m/1986787.1657666922%40sss.pgh.pa.us
This commit is contained in:
David Rowley
2022-07-13 15:03:47 +12:00
parent 50e4c280f0
commit c23e3e6beb
7 changed files with 25 additions and 30 deletions
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14
src/backend/optimizer/path/indxpath.c
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@@ -3026,14 +3026,12 @@ expand_indexqual_rowcompare(PlannerInfo *root,
rc->rctype = (RowCompareType) op_strategy;
rc->opnos = new_ops;
rc->opfamilies = list_truncate(list_copy(clause->opfamilies),
matching_cols);
rc->inputcollids = list_truncate(list_copy(clause->inputcollids),
matching_cols);
rc->largs = list_truncate(copyObject(var_args),
matching_cols);
rc->rargs = list_truncate(copyObject(non_var_args),
matching_cols);
rc->opfamilies = list_copy_head(clause->opfamilies,
matching_cols);
rc->inputcollids = list_copy_head(clause->inputcollids,
matching_cols);
rc->largs = list_copy_head(var_args, matching_cols);
rc->rargs = list_copy_head(non_var_args, matching_cols);
iclause->indexquals = list_make1(make_simple_restrictinfo(root,
(Expr *) rc));
}