UNION ALL queries are a subject of optimization introduced in MDEV-334
when creation of a temporary table is skipped.
While there is a check for this optimization in Explain_union::print_explain()
there was no such in Explain_union::print_explain_json(). This resulted in
printing irrelevant data like:
"union_result": {
"table_name": "<union2,3>",
"access_type": "ALL",
"r_loops": 0,
"r_rows": null
in case when creation of the temporary table was actually optimized out.
This commits adds a check whether the temporary table was actually created
during the UNION ALL processing and eliminates printing of the irrelevant data.
Count the "gap" time between table accesses and display it as
r_other_time_ms in the "table" element.
* The advantage of this approach is that it doesn't add any new
my_timer_cycles() calls.
* The disadvantage is that the definition of what is done during
"other time" is not that clear: it includes checking the WHERE
(for this table), constructing index lookup tuple (for the next table)
writing to GROUP BY temporary table (as we dont account for that time
separately [yet], etc)
The MDEV-20265 commit e746f451d5
introduces DBUG_ASSERT(right_op == r_tbl) in
st_select_lex::add_cross_joined_table(), and that assertion would
fail in several tests that exercise joins. That commit was skipped
in this merge, and a separate fix of MDEV-20265 will be necessary in 10.4.
This task involves the implementation for the optimizer trace.
This feature produces a trace for any SELECT/UPDATE/DELETE/,
which contains information about decisions taken by the optimizer during
the optimization phase (choice of table access method, various costs,
transformations, etc). This feature would help to tell why some decisions were
taken by the optimizer and why some were rejected.
Trace is session-local, controlled by the @@optimizer_trace variable.
To enable optimizer trace we need to write:
set @@optimizer_trace variable= 'enabled=on';
To display the trace one can run:
SELECT trace FROM INFORMATION_SCHEMA.OPTIMIZER_TRACE;
This task also involves:
MDEV-18489: Limit the memory used by the optimizer trace
introduces a switch optimizer_trace_max_mem_size which limits
the memory used by the optimizer trace. This was implemented by
Sergei Petrunia.
MDEV-17631 select_handler for a full query pushdown
Interfaces + Proof of Concept for federatedx with test cases.
The interfaces have been developed for integration of ColumnStore engine.
ANALYZE and ANALYZE FORMAT=JSON structures are changed in the way that they
show additional information when rowid filter is used:
- r_selectivity_pct - the observed filter selectivity
- r_buffer_size - the size of the rowid filter container buffer
- r_filling_time_ms - how long it took to fill rowid filter container
New class Rowid_filter_tracker was added. This class is needed to collect data
about how rowid filter is executed.
This patch contains a full implementation of the optimization
that allows to use in-memory rowid / primary filters built for range
conditions over indexes. In many cases usage of such filters reduce
the number of disk seeks spent for fetching table rows.
In this implementation the choice of what possible filter to be applied
(if any) is made purely on cost-based considerations.
This implementation re-achitectured the partial implementation of
the feature pushed by Galina Shalygina in the commit
8d5a11122c.
Besides this patch contains a better implementation of the generic
handler function handler::multi_range_read_info_const() that
takes into account gaps between ranges when calculating the cost of
range index scans. It also contains some corrections of the
implementation of the handler function records_in_range() for MyISAM.
This patch supports the feature for InnoDB and MyISAM.
subquery when ORDER BY is present
Currently for setting r_limit we divide with the number of iterations we invoke the dependent subquery.
This is not needed for the case of limit. For varying limits we produce the output that the limit varies with
execution.
Also there is a type for filtered , we forgot to multiply by 100 as it is represented as a percent.
Handle string length as size_t, consistently (almost always:))
Change function prototypes to accept size_t, where in the past
ulong or uint were used. change local/member variables to size_t
when appropriate.
This fix excludes rocksdb, spider,spider, sphinx and connect for now.
Most "new" failures fixed in the following files:
- sql_select.cc
- item.cc
- item_func.cc
- opt_subselect.cc
Other things:
- Allocate udf_handler strings in mem_root
- Required changes in sql_string.h
- Add mem_root as argument to some new [] calls
- Mark udf_handler strings as thread specific
- Removed some comment blocks with code
- Added sql/mariadb.h file that should be included first by files in sql
directory, if sql_plugin.h is not used (sql_plugin.h adds SHOW variables
that must be done before my_global.h is included)
- Removed a lot of include my_global.h from include files
- Removed include's of some files that my_global.h automatically includes
- Removed duplicated include's of my_sys.h
- Replaced include my_config.h with my_global.h
