After the commit b76b69cd5f
loose index scan for queries with DISTINCT stopped working.
That is why that commit has to be reverted.
Additionally this patch fixes the problem of MDEV-10880.
The issue was that r_loops, r_rows and r_filtered in ANALYZE FORMAT= JSON were not
calculated for the table on which we were performing the MRR scan in the BKA join
Fixed this by adding respective counter in the JOIN_TAB_SCAN_MRR::open and JOIN_TAB_SCAN_MRR::next
(Based on original patch by Sanja Byelkin)
Make the code that produces JSON output handle LooseScan quick select.
The output we produce is compatible with MySQL 5.6.
- Single_line_formatting_helper should not accidentally exit the
DISABLED state. No JSON construct should be able to move the
Single_line_formatting_helper from DISABLED state.
Switch EXPLAIN JSON from using subselect_engine::get_identifier()
to the number from Item_subselect::unit.
Remove subselect_union_engine::get_identifier() because it was added
only for EXPLAIN JSON code.
- Switch Explain data structure from "flat" representation of
SJ-Materialization into nested one.
- Update functions that print tabular output to operate on the
nested structure.
- Add function to generate JSON output.
- Basic support for JOIN buffering
- The output is not polished but catches the main point:
tab->select_cond and tab->cache_select->cond are printed separately.
- Hash join support is poor still.
- Also fixed identation in JOIN_TAB::save_explain_data
Writing JSON:
- Fix a bug in Single_line_formatting_helper
- Add Json_writer_nesting_guard - safety class
EXPLAIN JSON support
- Add basic subquery support
- Add tests for UNION/UNION ALL.
- Drop all tables in explain_json.test
- Tabular form should print ref='' when type='fulltext' (another peculiarity
of the traditional EXPLAIN format)
- String_list::append_str should allocate memory for \0, too
- Some temporary code for EXPLAIN JSON and join buffering.
