Fixed failing main.default on Windows
(to trigger an assert the test needed a debug build without
safemalloc, as 0xa5 happened to have the important bit set "correctly")
(This is the assert that was added in fix for MDEV-26047)
Table elimination may remove an ON expression from an outer join.
However SELECT_LEX::update_used_tables() will still call
item->walk(&Item::eval_not_null_tables)
for eliminated expressions. If the subquery is constant and cheap
Item_cond_and will attempt to evaluate it, which will trigger an
assert.
The fix is not to call update_used_tables() or eval_not_null_tables()
for ON expressions that were eliminated.
- Describe the lifetime of EXPLAIN data structures in
sql_explain.h:ExplainDataStructureLifetime.
- Make Item_field::set_field() call set_refers_to_temp_table()
when it refers to a temp. table.
- Introduce QT_DONT_ACCESS_TMP_TABLES flag for Item::print.
It directs Item_field::print to not try access its the
temp table.
- Introduce Explain_query::notify_tables_are_closed()
and call it right before the query closes its tables.
- Make Explain data stuctures' print_explain_json() methods
accept "no_tmp_tbl" parameter which means pass
QT_DONT_ACCESS_TMP_TABLES when printing items.
- Make Show_explain_request::call_in_target_thread() not call
set_current_thd(). This wasn't needed as the code inside
lex->print_explain() uses output->thd anyway. output->thd
refers to the SHOW command's THD object.
SHOW EXPLAIN/ANALYZE FORMAT=JSON tries to access items that have already been
freed by a call to free_items() during THD::cleanup_after_query().
The solution is to disallow APC calls including SHOW EXPLAIN/ANALYZE
just before the call to free_items().
This reverts commit 5ba77222e9
but keeps the test. A different fix for
MDEV-21028 Server crashes in Query_arena::set_query_arena upon SELECT from view
internal temporary tables should use THD as expr_area
The cause of the bug is overflow of uint16 KEY_PART_INFO::length and/or
uint16 KEY_PART_INFO::store_length. The solution is to increase the size
of those variables to the 'uint' type (which is 32-bit long)
If JOIN::create_postjoin_aggr_table encounters errors during execution
then free_tmp_table() is then called twice for JOIN_TAB::aggr.
The solution is to initialize JOIN_TAB::aggr only on successful completion
of JOIN::create_postjoin_aggr_table
Second execution of a prepared statement for a query containing a constant
subquery with union that can be optimized away, could result in server abnormal
termination for debug build or incorrect result set output for release build.
For example, the following test case crashes a server built with debug on second
run of the statement EXECUTE stmt
CREATE TABLE t1 (a INT);
PREPARE stmt FROM 'EXPLAIN SELECT * FROM t1 HAVING 6 IN ( SELECT 6 UNION SELECT 5 )';
EXECUTE stmt;
EXECUTE stmt;
The reason for incorrect result set output or abnormal server termination
is careless working with the data member fake_select_lex->options inside
the function mysql_explain_union(). Once the flag SELECT_DESCRIBE is set in
the data member fake_select_lex->option before calling the methods
SELECT_LEX_UNIT::prepare/SELECT_LEX_UNIT::execute
the original value of the option is no longer restored.
As a consequence, next time the prepared statement is re-executed we have
the fake_select_lex with the flag SELECT_DESCRIBE set in the data member
fake_select_lex->option, that is incorrect. In result, the method
Item_subselect::assigned()
is not invoked during evaluation of a constant condition (constant subquery
with union) that being performed on OPTIMIZE phase of query handling.
This leads to the fact that records in the temporary table are not deleted
before calling
table->file->ha_enable_indexes(HA_KEY_SWITCH_ALL)
in the method st_select_lex_unit::optimize().
In result table->file->ha_enable_indexes(HA_KEY_SWITCH_ALL) returns error
and DBUG_ASSERT(0) is fired.
Stack trace to the line where the error generated on re-enabling indexes
for next subselect iteration is below:
st_select_lex_unit::optimize (at sql_union.cc:954)
handler::ha_enable_indexes (at handler.cc:4338)
ha_heap::enable_indexes (at ha_heap.cc:519)
heap_enable_indexes (at hp_clear.c:164)
The code snippet to clarify raising the error is also listed:
int heap_enable_indexes(HP_INFO *info)
{
int error= 0;
HP_SHARE *share= info->s;
if (share->data_length || share->index_length)
error= HA_ERR_CRASHED; <<== set error the value HA_ERR_CRASHED
since share->data_length != 0
To fix this issue the original value of unit->fake_select_lex->options
has to be saved before setting the flag SELECT_DESCRIBE and restored
on return from invocation of SELECT_LEX_UNIT::prepare/SELECT_LEX_UNIT::execute
The problem was that "group_min_max optimization" does not work if
some aggregate functions, like COUNT(*), is used.
The function get_best_group_min_max() is using the join->sum_funcs
array to check which aggregate functions are used.
The bug was that aggregates in HAVING where not yet added to
join->sum_funcs at the time get_best_group_min_max() was called.
Fixed by populate join->sum_funcs already in prepare, which means that
all sum functions will be in join->sum_funcs in get_best_group_min_max().
A benefit of this approach is that we can remove several calls to
make_sum_func_list() from the code and simplify the function.
I removed some wrong setting of 'sort_and_group'.
This variable is set when alloc_group_fields() is called, as part
of allocating the cache needed by end_send_group() and does not need
to be set by other functions.
One problematic thing was that Spider is using *join->sum_funcs to detect
at which stage the optimizer is and do internal calculations of aggregate
functions. Updating join->sum_funcs early caused Spider to fail when trying
to find min/max values in opt_sum_query().
Fixed by temporarily resetting sum_funcs during opt_sum_query().
Reviewer: Sergei Petrunia
