This patch is the result of running
run-clang-tidy -fix -header-filter=.* -checks='-*,modernize-use-equals-default' .
Code style changes have been done on top. The result of this change
leads to the following improvements:
1. Binary size reduction.
* For a -DBUILD_CONFIG=mysql_release build, the binary size is reduced by
~400kb.
* A raw -DCMAKE_BUILD_TYPE=Release reduces the binary size by ~1.4kb.
2. Compiler can better understand the intent of the code, thus it leads
to more optimization possibilities. Additionally it enabled detecting
unused variables that had an empty default constructor but not marked
so explicitly.
Particular change required following this patch in sql/opt_range.cc
result_keys, an unused template class Bitmap now correctly issues
unused variable warnings.
Setting Bitmap template class constructor to default allows the compiler
to identify that there are no side-effects when instantiating the class.
Previously the compiler could not issue the warning as it assumed Bitmap
class (being a template) would not be performing a NO-OP for its default
constructor. This prevented the "unused variable warning".
When a range rowid filter was used with an index ref access the cost of
accessing the index entries for the records rejected by the filter was not
taken into account. For a ref access by an index with big average number
of records per key this led to poor execution plans if selectivity of the
used filter was high.
The patch resolves this problem. It also introduces a minor optimization
that skips look-ups into a filter that turns out to be empty.
With this patch the output of ANALYZE stmt reports the number of look-ups
into used rowid filters.
The patch also back-ports from 10.5 the code that properly sets the field
TABLE::file::table for opened temporary tables.
The test cases that were supposed to use rowid filters have been adjusted
in order to use similar execution plans after this fix.
Approved by Oleksandr Byelkin <sanja@mariadb.com>
- 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.
Due to inconsistent usage of different cost models to calculate
the cost of ref accesses we have to make the calculation of the
gain promising by usage a range filter more complex.
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.
