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MDEV-30806: ANALYZE FORMAT=JSON: better support for BNL and BNL-H joins

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In block-nl-join, add:

- r_loops - this shows how many incoming record combinations this
  query plan node had.

- r_effective_rows - this shows the average number of matching rows
  that this table had for each incoming record combination. This is
  comparable with r_rows in non-blocked access methods.
  For BNL-joins, it is always equal to
   $.table.r_rows * $.table.r_filtered
  For BNL-H joins the value cannot be computed from other values

Reviewed by: Monty <monty@mariadb.org>
This commit is contained in:
Sergei Petrunia
2023-03-07 19:49:57 +03:00
parent 169def14f6
commit dc1d6213f9
14 changed files with 279 additions and 30 deletions
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19
sql/sql_explain.cc
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@@ -1891,12 +1891,29 @@ void Explain_table_access::print_explain_json(Explain_query *query,
if (is_analyze)
{
//writer->add_member("r_loops").add_ll(jbuf_tracker.get_loops());
writer->add_member("r_loops").add_ll(jbuf_loops_tracker.get_loops());
writer->add_member("r_filtered");
if (jbuf_tracker.has_scans())
writer->add_double(jbuf_tracker.get_filtered_after_where()*100.0);
else
writer->add_null();
/*
effective_rows is average number of matches we got for an incoming
row. The row is stored in the join buffer and then is read
from there, possibly multiple times. We can't count this number
directly. Infer it as:
total_number_of_row_combinations_considered / r_loops.
*/
writer->add_member("r_effective_rows");
if (jbuf_loops_tracker.has_scans())
{
double loops= (double)jbuf_loops_tracker.get_loops();
double row_combinations= (double)jbuf_tracker.r_rows;
writer->add_double(row_combinations / loops);
}
else
writer->add_null();
}
}