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MDEV-21932 A fast plan with ROR index-merge is ignored when

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'index_merge_sort_union=off'

When index_merge_sort_union is set to 'off' and  index_merge_union is set
to 'on' then any evaluated index merge scan must consist only of ROR scans.
The cheapest out of such index merges must be chosen. This index merge
might not be the cheapest index merge.
This commit is contained in:
Igor Babaev
2020-03-12 23:50:20 -07:00
parent 3ab33c6c92
commit 5af12e4635
4 changed files with 108 additions and 1 deletions
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7
sql/opt_range.cc
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@ -6802,6 +6802,13 @@ static TRP_RANGE *get_key_scans_params(PARAM *param, SEL_TREE *tree,
update_tbl_stats, &mrr_flags,
&buf_size, &cost);
if (!param->is_ror_scan &&
!optimizer_flag(param->thd, OPTIMIZER_SWITCH_INDEX_MERGE_SORT_UNION))
{
/* The scan is not a ROR-scan, just skip it */
continue;
}
if (found_records != HA_POS_ERROR && tree->index_scans &&
(index_scan= (INDEX_SCAN_INFO *)alloc_root(param->mem_root,
sizeof(INDEX_SCAN_INFO))))