The issue here is when records are read from the temporary file
(filesort result in this case) via a cache(rr_from_cache).
The cache is initialized with init_rr_cache.
For correlated subquery the cache allocation is happening at each execution
of the subquery but the deallocation happens only once and that was
when the query execution was done.
So generally for subqueries we do two types of cleanup
1) Full cleanup: we should free all resources of the query(like temp tables).
This is done generally when the query execution is complete or the subquery
re-execution is not needed (case with uncorrelated subquery)
2) Partial cleanup: Minor cleanup that is required if
the subquery needs recalculation. This is done for all the structures that
need to be allocated for each execution (example SORT_INFO for filesort
is allocated for each execution of the correlated subquery).
The fix here would be free the cache used by rr_from_cache in the partial
cleanup phase.
For the case when the SJM scan table is the first table in the join order,
then if we want to do the sorting on the SJM scan table, then we need to
make sure that we unpack the values to base table fields in two cases:
1) Reading the SJM table and writing the sort-keys inside the sort-buffer
2) Reading the sorted data from the sort file
A temporary table is needed for window function computation but if only a NAMED WINDOW SPEC
is used and there is no window function, then there is no need to create a temporary
table as there is no stage to compute WINDOW FUNCTION
The issue here is for degenerate joins we should execute the window
function but it is not getting executed in all the cases.
To get the window function values window function needs to be executed
always. This currently does not happen in few cases
where the join would return 0 or 1 row like
1) IMPOSSIBLE WHERE
2) MIN/MAX optimization
3) EMPTY CONST TABLE
The fix is to make sure that window functions get executed
and the temporary table is setup for the execution of window functions
because internally setup_wild() adjusts select_lex->with_wild directly
anyway, so there is no reason to pretend that the number of '*' may be
anything else but select_lex->with_wild
And don't update select_lex->item_list, because fields can come
from anywhere and don't necessarily have to be copied into select_lex.
best_access_path() is called from two optimization phases:
1. Plan choice phase, in choose_plan(). Here, the join prefix being
considered is in join->positions[]
2. Plan refinement stage, in fix_semijoin_strategies_for_picked_join_order
Here, the join prefix is in join->best_positions[]
It used to access join->positions[] from stage #2. This didnt cause any
valgrind or asan failures (as join->positions[] has been written-to before)
but the effect was similar to that of reading the random data:
The join prefix we've picked (in join->best_positions) could have
nothing in common with the join prefix that was last to be considered
(in join->positions).
This patch introduces the optimization that allows range optimizer to
consider index range scans that are built employing NOT NULL predicates
inferred from WHERE conditions and ON expressions.
The patch adds a new optimizer switch not_null_range_scan.
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 bug is caused by pushdown from HAVING into WHERE.
It appears because condition that is pushed wasn't fixed.
It is also discovered that condition pushdown from HAVING into
WHERE is done wrong. There is no need to build clones for some
conditions that can be pushed. They can be simply moved from HAVING
into WHERE without cloning.
build_pushable_cond_for_having_pushdown(),
remove_pushed_top_conjuncts_for_having() methods are changed.
It is found that there is no transformation made for fields of
pushed condition.
field_transformer_for_having_pushdown transformer is added.
New tests are added. Some comments are changed.
The MDEV-17262 commit 26432e49d3
was skipped. In Galera 4, the implementation would seem to require
changes to the streaming replication.
In the tests archive.rnd_pos main.profiling, disable_ps_protocol
for SHOW STATUS and SHOW PROFILE commands until MDEV-18974
has been fixed.
