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bug-114885/115353 Setting index_merge_union=off can result in an inc… #569

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bug-114885/115353 Setting index_merge_union=off can result in an inc… #569

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6 changes: 5 additions & 1 deletion sql/range_optimizer/range_optimizer.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -1028,6 +1028,7 @@ static AccessPath *get_best_disjunct_quick(
bool all_scans_rors = true;
bool imerge_too_expensive = false;
AccessPath **cur_child = range_scans;
uint cannot_be_used_for_imerge_count = 0;
for (auto tree_it = imerge->trees.begin(); tree_it != imerge->trees.end();
++tree_it, cur_child++) {
DBUG_EXECUTE("info",
Expand Down Expand Up @@ -1056,6 +1057,7 @@ static AccessPath *get_best_disjunct_quick(
if (!child_param.can_be_used_for_imerge) {
trace_idx.add("chosen", false)
.add_alnum("cause", "index has DESC key part");
cannot_be_used_for_imerge_count++;
continue;
}

Expand All @@ -1082,7 +1084,9 @@ static AccessPath *get_best_disjunct_quick(
((non_cpk_scan_records + cpk_scan_records >=
table->file->stats.records) &&
read_cost != DBL_MAX)) &&
!force_index_merge)) {
!force_index_merge) ||
(!index_merge_union_allowed &&
cannot_be_used_for_imerge_count == imerge->trees.size())) {
/*
Bail out if it is obvious that both index_merge and ROR-union will be
more expensive
Expand Down