maria-developers team mailing list archive

[Sergey Petrunia <sergey@xxxxxxxxxxx>]

Hello Igor,

I have pushed into 10.4-mdev16188 tree a patch that adds EXPLAIN FORMAT=JSON
support. There is no ANALYZE support, yet.

main.rowid_filter has an example of EXPLAIN FORMAT=JSON at the bottom. The
filter is described like so:

+      "rowid_filter": {
+        "range": {
+          "key": "i_l_shipdate",
+          "used_key_parts": ["l_shipDATE"]
+        },
+        "rows": 8,
+        "selectivity_pct": 0.1332
+      },

Here "rows" is how many rows we will get from the quick select that is used to
build the filter.

selectivity_pct is the selectivity of the filter.

You will also notice this change from (1%) to (0%):

-1      SIMPLE  lineitem        range|filter    PRIMARY,i_l_shipdate,i_l_receiptdate,i_l_orderkey,i_l_orderkey_quantity i_l_receiptdate|i_l_shipdate    4|4     NULL      6 (1%)  Using index condition; Using where; Using filter
+1      SIMPLE  lineitem        range|filter    PRIMARY,i_l_shipdate,i_l_receiptdate,i_l_orderkey,i_l_orderkey_quantity i_l_receiptdate|i_l_shipdate    4|4     NULL      6 (0%)  Using index condition; Using where; Using filter

This is because the original code had a piece of logic in
JOIN_TAB::save_filter_explain_data: print "1%" if it was "0%".

I'm wondering, is there any reason we cannot print the number with greater
precision in this case?


BR
 Sergei
-- 
Sergei Petrunia, Software Developer
MariaDB Corporation | Skype: sergefp | Blog: http://s.petrunia.net/blog