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MDEV-24224 Gap lock on delete in 10.5 using READ COMMITTED

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When MDEV-19544 (commit 1a6f470464)
simplified the initialization of the local variable
set_also_gap_locks, an inadvertent change was included.
Essentially, all code branches that are executed when
set_also_gap_locks hold must also ensure that
trx->isolation_level > TRX_ISO_READ_COMMITTED holds.
This was being violated in a few code paths.

It turns out that there is an even simpler fix: Remove the test
of thd_is_select() completely. In that way, the first part of
UPDATE or DELETE should work exactly like SELECT...FOR UPDATE.

thd_is_select(): Remove.
This commit is contained in:
Marko Mäkelä 2020-11-18 10:27:18 +02:00
parent fabdad6857
commit 33d41167c5
5 changed files with 78 additions and 27 deletions
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35
mysql-test/suite/innodb/r/gap_locks.result Normal file
View file

@ -0,0 +1,35 @@
CREATE TABLE t1(a INT PRIMARY KEY, b VARCHAR(40), c INT, INDEX(b,c))
ENGINE=InnoDB;
INSERT INTO t1 VALUES (1,'1',1),(2,'2',1);
SET @save_locks= @@GLOBAL.innodb_status_output_locks;
SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = 'ON';
SET TRANSACTION ISOLATION LEVEL SERIALIZABLE;
BEGIN;
DELETE FROM t1 WHERE b='2' AND c=2;
SHOW ENGINE INNODB STATUS;
Type Name Status
InnoDB 2 lock struct(s), 1 row lock(s)
ROLLBACK;
SET TRANSACTION ISOLATION LEVEL REPEATABLE READ;
BEGIN;
DELETE FROM t1 WHERE b='2' AND c=2;
SHOW ENGINE INNODB STATUS;
Type Name Status
InnoDB 2 lock struct(s), 1 row lock(s)
ROLLBACK;
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
BEGIN;
DELETE FROM t1 WHERE b='2' AND c=2;
SHOW ENGINE INNODB STATUS;
Type Name Status
InnoDB 1 lock struct(s), 0 row lock(s)
ROLLBACK;
SET TRANSACTION ISOLATION LEVEL READ UNCOMMITTED;
BEGIN;
DELETE FROM t1 WHERE b='2' AND c=2;
SHOW ENGINE INNODB STATUS;
Type Name Status
InnoDB 1 lock struct(s), 0 row lock(s)
ROLLBACK;
SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = @save_locks;
DROP TABLE t1;

29
mysql-test/suite/innodb/t/gap_locks.test Normal file
View file

@ -0,0 +1,29 @@
--source include/have_innodb.inc
CREATE TABLE t1(a INT PRIMARY KEY, b VARCHAR(40), c INT, INDEX(b,c))
ENGINE=InnoDB;
INSERT INTO t1 VALUES (1,'1',1),(2,'2',1);
SET @save_locks= @@GLOBAL.innodb_status_output_locks;
SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = 'ON';
let $isolation= 4;
while ($isolation) {
let $tx_isolation= `SELECT CASE $isolation
WHEN 1 THEN 'READ UNCOMMITTED'
WHEN 2 THEN 'READ COMMITTED'
WHEN 3 THEN 'REPEATABLE READ'
ELSE 'SERIALIZABLE' END`;
eval SET TRANSACTION ISOLATION LEVEL $tx_isolation;
BEGIN;
DELETE FROM t1 WHERE b='2' AND c=2;
--replace_regex /.*(\d+ lock struct...), heap size \d+(, \d+ row lock...).*/\1\2/
SHOW ENGINE INNODB STATUS;
ROLLBACK;
dec $isolation;
}
SET GLOBAL INNODB_STATUS_OUTPUT_LOCKS = @save_locks;
DROP TABLE t1;

13
storage/innobase/handler/ha_innodb.cc
View file

@ -1495,7 +1495,7 @@ thd_trx_is_auto_commit(
&& !thd_test_options(
thd,
OPTION_NOT_AUTOCOMMIT | OPTION_BEGIN)
&& thd_is_select(thd));
&& thd_sql_command(thd) == SQLCOM_SELECT);
}
/******************************************************************//**
@ -1531,17 +1531,6 @@ thd_query_start_micro(
return thd_start_utime(thd);
}
/******************************************************************//**
Returns true if the thread is executing a SELECT statement.
@return true if thd is executing SELECT */
ibool
thd_is_select(
/*==========*/
const THD* thd) /*!< in: thread handle */
{
return(thd_sql_command(thd) == SQLCOM_SELECT);
}
/******************************************************************//**
Returns the lock wait timeout for the current connection.
@return the lock wait timeout, in seconds */

8
storage/innobase/include/ha_prototypes.h
View file

@ -190,14 +190,6 @@ const char*
innobase_basename(
const char* path_name);
/******************************************************************//**
Returns true if the thread is executing a SELECT statement.
@return true if thd is executing SELECT */
ibool
thd_is_select(
/*==========*/
const THD* thd); /*!< in: thread handle */
/******************************************************************//**
Converts an identifier to a table name. */
void

20
storage/innobase/row/row0sel.cc
View file

@ -4542,12 +4542,11 @@ aborted:
|| prebuilt->table->no_rollback()
|| srv_read_only_mode);
/* Do not lock gaps for plain SELECT
at READ UNCOMMITTED or READ COMMITTED isolation level */
/* Do not lock gaps at READ UNCOMMITTED or READ COMMITTED
isolation level */
const bool set_also_gap_locks =
prebuilt->select_lock_type != LOCK_NONE
&& (trx->isolation_level > TRX_ISO_READ_COMMITTED
|| !thd_is_select(trx->mysql_thd))
&& trx->isolation_level > TRX_ISO_READ_COMMITTED
#ifdef WITH_WSREP
&& !wsrep_thd_skip_locking(trx->mysql_thd)
#endif /* WITH_WSREP */
@ -4755,7 +4754,6 @@ rec_loop:
if (page_rec_is_supremum(rec)) {
if (set_also_gap_locks
&& trx->isolation_level > TRX_ISO_READ_COMMITTED
&& !dict_index_is_spatial(index)) {
/* Try to place a lock on the index record */
@ -5020,8 +5018,16 @@ wrong_offs:
goto no_gap_lock;
}
if (!set_also_gap_locks
|| (unique_search && !rec_get_deleted_flag(rec, comp))
#ifdef WITH_WSREP
if (UNIV_UNLIKELY(!set_also_gap_locks)) {
ut_ad(wsrep_thd_skip_locking(trx->mysql_thd));
goto no_gap_lock;
}
#else /* WITH_WSREP */
ut_ad(set_also_gap_locks);
#endif /* WITH_WSREP */
if ((unique_search && !rec_get_deleted_flag(rec, comp))
|| dict_index_is_spatial(index)) {
goto no_gap_lock;