best_extension_by_limited_search() assumes that tables should be sorted
according to size to be able to quickly disregard bad plans. However the
current usage of swap_variables() will change the table order to a not
sorted one for the next recursive call. This breaks the assumtion and
causes performance issues when using many tables (we have to examine
many more plans).
This patch fixes this by ensuring that the original table order is kept
for the not yet used tables when best_extension_by_limited_search() is
called.
This was done by always calling swap_variables() for each table and
restoring the original table order at exit.
Some test changed:
- In a majority of the test the change was that two "identical tables"
where swapped and the optimzer is now using the first/smaller table
- In few test the table order was changed. The new plan looks identical
or slighly better than the original.
The issue was that best_extension_by_limited_search() had to go through
too many plans with the same cost as there where many EQ_REF tables.
Fixed by shortcutting EQ_REF (AND REF) when the result only contains one
row. This got the optimization time down from hours to sub seconds.
The only known downside with this patch is that in some cases a table
with ref and 1 record may be used before on EQ_REF table. The faster
optimzation phase should compensate for this.
make_join_select() calls const_cond->val_int(). There are edge cases
where const_cond may have a not-yet optimized subquery.
(The subquery will have used_tables() covered by join->const_tables. It
will still have const_item()==false, so other parts of the optimizer
will not try to evaluate it. We should probably mark such subqueries
as constant but that is outside the scope of this MDEV)
In mysql_execute_command(), move optimizer trace initialization to be
after run_set_statement_if_requested() call.
Unfortunately, mysql_execute_command() code uses "goto error" a lot, and
this means optimizer trace code cannot use RAII objects. Work this around
by:
- Make Opt_trace_start a non-RAII object, add init() method.
- Move the code that writes the top-level object and array into
Opt_trace_start::init().
This enables optimizer_trace output for the next SQL command.
Identical as if one would have done:
- Store value of @@optimizer_trace
- Set @optimizer_trace="enabled=on"
- Run query
- SELECT * from OPTIMIZER_TRACE
- Restore value of @@optimizer_trace
This is a great time saver when one wants to quickly check the optimizer
trace for a query in a mtr test.
if a query used no fields from an I_S table, we were creating a temp
table with one, first, field (as a table cannot have zero fields),
with its length truncated to 1.
Now - force also this dummy field to be a normal field, not a BLOB
Make sure to initialize members of TABLE::reginfo when TABLE::init is called. In this case the problem
was that table->reginfo.join_tab was set for the SELECT query and then was reused by the UPDATE query.
This case occurred only when the SELECT query had a degenerate join.
KEY_MULTI_RANGE::range_flag does not have correct flag bits for
per-endpoint flags (NEAR_MIN, NEAR_MAX, NO_MIN_RANGE, NO_MAX_RANGE).
It only has bits for flags that describe both endpoints.
So
- Document this.
- Switch optimizer trace to using {start|end}_key.flag values, instead.
This fixes the bug.
- Switch records_in_column_ranges() to doing that too. (This used to
work, because KEY_MULTI_RANGE::range_flag had correct flag value
for the last key component, and EITS only uses one-component
pseudo-indexes)
sprintf() format of double changed from '%lg' to '%-.11lg'
The change was to make it easier to read optimizer trace output
with tables that has millions of records.
- Print the rowid filters that are available for use with each table.
- Make print_best_access_for_table() print which filter it has picked.
- Make best_access_path() print the filter for considered ref accesses.
- multi_range_read_info_const now uses the new records_in_range interface
- Added handler::avg_io_cost()
- Don't calculate avg_io_cost() in get_sweep_read_cost if avg_io_cost is
not 1.0. In this case we trust the avg_io_cost() from the handler.
- Changed test_quick_select to use TIME_FOR_COMPARE instead of
TIME_FOR_COMPARE_IDX to align this with the rest of the code.
- Fixed bug when using test_if_cheaper_ordering where we didn't use
keyread if index was changed
- Fixed a bug where we didn't use index only read when using order-by-index
- Added keyread_time() to HEAP.
The default keyread_time() was optimized for blocks and not suitable for
HEAP. The effect was the HEAP prefered table scans over ranges for btree
indexes.
- Fixed get_sweep_read_cost() for HEAP tables
- Ensure that range and ref have same cost for simple ranges
Added a small cost (MULTI_RANGE_READ_SETUP_COST) to ranges to ensure
we favior ref for range for simple queries.
- Fixed that matching_candidates_in_table() uses same number of records
as the rest of the optimizer
- Added avg_io_cost() to JT_EQ_REF cost. This helps calculate the cost for
HEAP and temporary tables better. A few tests changed because of this.
- heap::read_time() and heap::keyread_time() adjusted to not add +1.
This was to ensure that handler::keyread_time() doesn't give
higher cost for heap tables than for normal tables. One effect of
this is that heap and derived tables stored in heap will prefer
key access as this is now regarded as cheap.
- Changed cost for index read in sql_select.cc to match
multi_range_read_info_const(). All index cost calculation is now
done trough one function.
- 'ref' will now use quick_cost for keys if it exists. This is done
so that for '=' ranges, 'ref' is prefered over 'range'.
- scan_time() now takes avg_io_costs() into account
- get_delayed_table_estimates() uses block_size and avg_io_cost()
- Removed default argument to test_if_order_by_key(); simplifies code
This was to remove a performance regression between 10.3 and 10.4
In 10.5 we will have a better implementation of records_in_range
that will enable us to get more statistics.
This change was not done in 10.4 because the 10.5 will be part of
a larger change that is not suitable for the GA 10.4 version
Other things:
- Changed default handler block_size to 8192 to fix things statistics
for engines that doesn't set the block size.
- Fixed a bug in spider when using multiple part const ranges
(Patch from Kentoku)
Introduced a print_key_value function to makes sure that the trace prints data in readable format
for readable characters and the rest of the characters are printed as hexadecimal.
Changed the function append_range_all_keyparts to use sel_arg_range_seq_init / sel_arg_range_seq_next to produce ranges.
Also adjusted to print format for the ranges, now the ranges are printed as:
(keypart1_min, keypart2_min,..) OP (keypart1_name,keypart2_name, ..) OP (keypart1_max,keypart2_max, ..)
Also added more tests for range and index merge access for optimizer trace
