Basic variant of the fix: do not consider conditions in form
unique_key NOT IN (c1,c2...)
to be sargable. If there are only a few constants, the condition
is not selective. If there are a lot constants, the overhead of
processing such a huge range list is not worth it.
(Backport to 10.2)
This bug could manifest itself for a query with WHERE condition containing
top level OR formula such that each conjunct contained a single-range
condition supported by the same index. One of these range conditions must
be fully covered by another range condition that is used later in the OR
formula. Additionally at least one of these condition should be ANDed with
a sargable range condition supported by a different index.
There were several attempts to fix related problems for OR conditions after
the backport of range optimizer code from MySQL (commit
0e19f3e36f). Unfortunately the first of these
fixes contained typo remained unnoticed until recently. This typo bug led
to rejection of valid range accesses. This patch fixed this typo bug.
The fix revealed another two bugs: one in a constructor for SEL_ARG,
the other in the function tree_or(). Both are fixed in this patch.
Part#1: Revert the patch that caused it:
commit 291be49474
Author: Igor Babaev <igor@askmonty.org>
Date: Thu Sep 24 22:02:00 2020 -0700
MDEV-23811: With large number of indexes optimizer chooses an inefficient plan
This bug could manifest itself for a query with WHERE condition containing
top level OR formula such that each conjunct contained a single-range
condition supported by the same index. One of these range conditions must
be fully covered by another range condition that is used later in the OR
formula. Additionally at least one of these condition should be ANDed with
a sargable range condition supported by a different index.
There were several attempts to fix related problems for OR conditions after
the backport of range optimizer code from MySQL (commit
0e19f3e36f). Unfortunately the first of these
fixes contained typo remained unnoticed until recently. This typo bug led
to rejection of valid range accesses. This patch fixed this typo bug.
The fix revealed another two bugs: one in a constructor for SEL_ARG,
the other in the function tree_or(). Both are fixed in this patch.
When index_merge_sort_union is turned off only ror scans were considered for range
scans, which is wrong.
To fix the problem ensure both ror scans and non ror scans are considered for range
access
This allows one to run the test suite even if any of the following
options are changed:
- character-set-server
- collation-server
- join-cache-level
- log-basename
- max-allowed-packet
- optimizer-switch
- query-cache-size and query-cache-type
- skip-name-resolve
- table-definition-cache
- table-open-cache
- Some innodb options
etc
Changes:
- Don't print out the value of system variables as one can't depend on
them to being constants.
- Don't set global variables to 'default' as the default may not
be the same as the test was started with if there was an additional
option file. Instead save original value and reset it at end of test.
- Test that depends on the latin1 character set should include
default_charset.inc or set the character set to latin1
- Test that depends on the original optimizer switch, should include
default_optimizer_switch.inc
- Test that depends on the value of a specific system variable should
set it in the test (like optimizer_use_condition_selectivity)
- Split subselect3.test into subselect3.test and subselect3.inc to
make it easier to set and reset system variables.
- Added .opt files for test that required specfic options that could
be changed by external configuration files.
- Fixed result files in rockdsb & tokudb that had not been updated for
a while.
The error message modified.
Then the TABLE_SHARE::error_table_name() implementation taken from 10.3,
to be used as a name of the table in this message.
This patch introduces support for the system variable eq_range_index_dive_limit
that existed in MySQL starting from 5.6. The variable sets a limit for
index dives into equality ranges. Index dives are performed by optimizer
to estimate the number of rows in range scans. Index dives usually provide
good estimate but they are pretty expensive. To estimate the number of rows
in equality ranges statistical data on indexes can be employed. Its usage gives
not so good estimates but it's cheap. So if the number of equality dives
required by an index scan exceeds the set limit no dives for equality
ranges are performed by the optimizer for this index.
As the new system variable is introduced in a stable version the default
value for it is set to a special value meaning there is no limit for the number
of index dives performed by the optimizer.
The patch partially uses the MySQL code for WL 5957
'Statistics-based Range optimization for many ranges'.
Refactor get_datetime_value() not to create Item_cache_temporal(),
but do it always in ::fix_fields() or ::fix_length_and_dec().
Creating items at the execution time doesn't work very well with
virtual columns and check constraints that are fixed and executed
in different THDs.
Fixed handling of default values with cached temporal functions so that the
CREATE TABLE statement now succeeds.
Fixed virtual column session cleanup.
Fixed the error message.
Added quoting of date/time values in cases when this was omitted.
Added a test case in default.test.
Updated test result files.
The patch actually fixes the old defect of the optimizer that
could not extract keys for range access from IN predicates
with row arguments.
This problem was resolved in the mysql-5.7 code. The patch
supersedes what was done there:
- it can build range access when not all components of
the first row argument are refer to the columns of the table
for which the range access is constructed.
- it can use equality predicates to build range access
to the table that is not referred to in this argument.
Fix get_quick_keys(): When building range tree from a condition
in form
keypart1=const AND (keypart2 < 0 OR keypart2>=0)
the SEL_ARG for keypart2 represents an interval (-inf, +inf).
However, the logic that sets UNIQUE_RANGE flag fails to recognize
this, and sets UNIQUE_RANGE flag if (keypart1, keypart2) covered
a unique key.
As a result, range access executor assumes the interval can have
at most one row and only reads the first row from it.
Let range optimizer remove parts of OR-clauses for which range analysis
produced SEL_TREE(IMPOSSIBLE).
There is no need to remove parts of AND-clauses: either they are inside
of OR (and the whole AND-clause will be removed), or the AND-clause is
at the top level, in which case the whole WHERE (or ON) is always FALSE
and this is a degenerate case which receives special treatment.
The removal process takes care not to produce 1-way ORs (in that case
we substitute the OR for its remaining member).
- When range optimizer cannot the lookup value into [VAR]CHAR(n) column,
it should produce:
= "Impossible range" for equality
= "no range" for non-equalities.
Port to mariadb-1.0 the following fix from mysql-5.6:
Revision ID: jorgen.loland@oracle.com-20120314131055-ml54x9deueqfsff4
BUG#13701206: WHERE A>=B DOES NOT GIVE SAME EXECUTION PLAN
AS WHERE B<=A (RANGE OPTIMIZER)
that fix didn't have a public testcase, so I created one.
BNL and BNLH joins pre-filter the records from a joined table via JOIN_TAB::cache_select->cond.
There is no need to re-evaluate the same conditions via JOIN_TAB::select_cond. This patch removes
the duplicated conditions from the top-level conjuncts of each pushed condition.
The added "Using where" in few EXPLAINs is due to taking into account tab->cache_select->cond
in addition to tab->select_cond in JOIN::save_explain_data_intern.
This a an old legacy performance bug.
When a very selective range scan existed for the second table in a join,
and, at the same time, there was another range condition depending on the
fields of the first table, the optimizer chose a plan with
'Range checked for each record'. This plan was extremely inefficient in
comparison with the regular selective range scan.
As a matter of fact the range scan chosen for each record was the same as
that selective range scan.
Changed the test case for bug 24776 to preserve the old output for explain.
- Modify the way Item_cond::fix_fields() and Item_cond::eval_not_null_tables()
calculate bitmap for Item_cond_or::not_null_tables():
if they see a "... OR inexpensive_const_false_item OR ..." then the item can
be ignored.
- Updated test results. There can be more warnings produced since parts of WHERE
are evaluated more times.
from MariaDB 10.0.
The bug in mdev-3948 was an instance of the problem fixed by Sergey's patch
in 10.0 - namely that the range optimizer could change table->[read | write]_set,
and not restore it.
revno: 3471
committer: Sergey Petrunya <psergey@askmonty.org>
branch nick: 10.0-serg-fix-imerge
timestamp: Sat 2012-11-03 12:24:36 +0400
message:
# MDEV-3817: Wrong result with index_merge+index_merge_intersection, InnoDB table, join, AND and OR conditions
Reconcile the fixes from:
#
# guilhem.bichot@oracle.com-20110805143029-ywrzuz15uzgontr0
# Fix for BUG#12698916 - "JOIN QUERY GIVES WRONG RESULT AT 2ND EXEC. OR
# AFTER FLUSH TABLES [-INT VS NULL]"
#
# guilhem.bichot@oracle.com-20111209150650-tzx3ldzxe1yfwji6
# Fix for BUG#12912171 - ASSERTION FAILED: QUICK->HEAD->READ_SET == SAVE_READ_SET
# and
#
and related fixes from: BUG#1006164, MDEV-376:
Now, ROR-merged QUICK_RANGE_SELECT objects make no assumptions about the values
of table->read_set and table->write_set.
Each QUICK_ROR_SELECT has (and had before) its own column bitmap, but now, all
QUICK_ROR_SELECT's functions that care: reset(), init_ror_merged_scan(), and
get_next() will set table->read_set when invoked and restore it back to what
it was before the call before they return.
This allows to avoid the mess when somebody else modifies table->read_set for
some reason.
