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MDEV-20371: Invalid reads at plan refinement stage: join->positions...

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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 commit is contained in:
Sergei Petrunia
2019-09-10 23:51:42 +03:00
parent 863a951731
commit c8dc866fde
4 changed files with 52 additions and 28 deletions
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8
sql/sql_select.h
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@@ -792,6 +792,7 @@ public:
friend void best_access_path(JOIN *join,
JOIN_TAB *s,
table_map remaining_tables,
const struct st_position *join_positions,
uint idx,
bool disable_jbuf,
double record_count,
@@ -1960,6 +1961,11 @@ protected:
}
};
void best_access_path(JOIN *join, JOIN_TAB *s,
table_map remaining_tables,
const POSITION *join_positions, uint idx,
bool disable_jbuf, double record_count,
POSITION *pos, POSITION *loose_scan_pos);
bool cp_buffer_from_ref(THD *thd, TABLE *table, TABLE_REF *ref);
bool error_if_full_join(JOIN *join);
int report_error(TABLE *table, int error);
@@ -2277,7 +2283,7 @@ bool instantiate_tmp_table(TABLE *table, KEY *keyinfo,
ulonglong options);
bool open_tmp_table(TABLE *table);
void setup_tmp_table_column_bitmaps(TABLE *table, uchar *bitmaps);
double prev_record_reads(POSITION *positions, uint idx, table_map found_ref);
double prev_record_reads(const POSITION *positions, uint idx, table_map found_ref);
void fix_list_after_tbl_changes(SELECT_LEX *new_parent, List<TABLE_LIST> *tlist);
struct st_cond_statistic