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MDEV-39440: replay context throwed a warning for a query after altering an index #5064

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MDEV-39440: replay context throwed a warning for a query after altering an index #5064

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23 changes: 23 additions & 0 deletions mysql-test/main/opt_context_replay_basic.result
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Original file line number Diff line number Diff line change
Expand Up @@ -272,5 +272,28 @@ set optimizer_replay_context='opt_context';
EXPLAIN SELECT MAX(a) FROM t1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL Select tables optimized away
set optimizer_replay_context='';
drop table t1;
#
# MDEV-39440: replay context doesn't work after altering the index
#
create table t1 (btn char(10) not null, key using HASH (btn)) engine=heap;
insert into t1 values ("a"),("b"),("c"),("d");
alter table t1 add column new_col char(1) not null, add key using HASH (btn,new_col), drop key btn;
update t1 set new_col=left(btn,1);
set optimizer_record_context=1;
explain select * from t1 where btn="a";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL btn NULL NULL NULL 4 Using where
select context into dumpfile "../../tmp/dump1.sql"
from information_schema.optimizer_context;
set optimizer_record_context=0;
drop table t1;
set optimizer_replay_context='opt_context';
# Same query as above, must have same explain:
explain select * from t1 where btn="a";
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL btn NULL NULL NULL 4 Using where
set optimizer_replay_context='';
drop table t1;
drop database db1;
28 changes: 28 additions & 0 deletions mysql-test/main/opt_context_replay_basic.test
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Original file line number Diff line number Diff line change
Expand Up @@ -116,6 +116,34 @@ set optimizer_replay_context='opt_context';
--echo # Same query as above, must have same explain:
EXPLAIN SELECT MAX(a) FROM t1;

set optimizer_replay_context='';
--remove_file "$MYSQLTEST_VARDIR/tmp/dump1.sql"
drop table t1;

--echo #
--echo # MDEV-39440: replay context doesn't work after altering the index
--echo #
create table t1 (btn char(10) not null, key using HASH (btn)) engine=heap;
insert into t1 values ("a"),("b"),("c"),("d");
alter table t1 add column new_col char(1) not null, add key using HASH (btn,new_col), drop key btn;
update t1 set new_col=left(btn,1);

set optimizer_record_context=1;
explain select * from t1 where btn="a";
select context into dumpfile "../../tmp/dump1.sql"
from information_schema.optimizer_context;
set optimizer_record_context=0;
drop table t1;
--disable_query_log
--disable_result_log
--source "$MYSQLTEST_VARDIR/tmp/dump1.sql"
--enable_query_log
--enable_result_log
set optimizer_replay_context='opt_context';
--echo # Same query as above, must have same explain:
explain select * from t1 where btn="a";

set optimizer_replay_context='';
--remove_file "$MYSQLTEST_VARDIR/tmp/dump1.sql"
drop table t1;

Expand Down
25 changes: 15 additions & 10 deletions sql/opt_range.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -12471,6 +12471,13 @@ ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
ha_rows replay_ctx_max_index_blocks;
ha_rows replay_ctx_max_row_blocks;
bool replay_ctx_rc;
Optimizer_context_recorder *rec;
TABLE::OPT_RANGE *range= param->table->opt_range + keynr;
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@gemini-code-assist gemini-code-assist Bot May 11, 2026

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high

The range->max_index_blocks and range->max_row_blocks fields are only assigned values when rows != HA_POS_ERROR (lines 12557-12561 in the original code). Since the recording logic has been moved outside of this conditional block (lines 12591-12597), these fields will contain uninitialized values when rows == HA_POS_ERROR, which are then passed to rec->record_multi_range_read_info_const. These should be initialized to a safe default value (e.g., 0) to avoid recording garbage data and potential undefined behavior.

  TABLE::OPT_RANGE *range= param->table->opt_range + keynr;
  range->max_index_blocks= range->max_row_blocks= 0;

if (range)
{
range->max_index_blocks= 0;
range->max_row_blocks= 0;
}
DBUG_ENTER("check_quick_select");

/* Range not calculated yet */
Expand Down Expand Up @@ -12534,7 +12541,6 @@ ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
param->quick_rows[keynr]= rows;
if (rows != HA_POS_ERROR)
{
TABLE::OPT_RANGE *range= param->table->opt_range + keynr;
ha_rows table_records= param->table->stat_records();
if (rows > table_records)
{
Expand All @@ -12560,15 +12566,6 @@ ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
range->max_row_blocks=
MY_MIN(file->row_blocks(), rows * file->stats.block_size / IO_SIZE);

if (Optimizer_context_recorder *rec= param->thd->opt_ctx_recorder)
{
Range_print_enumerator_impl range_iter(param, idx, tree);
rec->record_multi_range_read_info_const(param->table->pos_in_table_list,
keynr, &range_iter, rows, cost,
range->max_index_blocks,
range->max_row_blocks);
}

if (update_tbl_stats)
{
param->table->opt_range_keys.set_bit(keynr);
Expand Down Expand Up @@ -12597,6 +12594,14 @@ ha_rows check_quick_select(PARAM *param, uint idx, ha_rows limit,
}
}

if (range && (rec= param->thd->opt_ctx_recorder))
{
Range_print_enumerator_impl range_iter(param, idx, tree);
rec->record_multi_range_read_info_const(
param->table->pos_in_table_list, keynr, &range_iter, rows, cost,
range->max_index_blocks, range->max_row_blocks);
}

/* Figure out if the key scan is ROR (returns rows in ROWID order) or not */
enum ha_key_alg key_alg= param->table->key_info[seq.real_keyno].algorithm;
if ((key_alg != HA_KEY_ALG_BTREE) && (key_alg!= HA_KEY_ALG_UNDEF))
Expand Down
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