mirror of
https://github.com/MariaDB/server.git
synced 2025-07-29 05:21:33 +03:00
Implement new type-of-operation-aware metadata locks.
Add a wait-for graph based deadlock detector to the MDL subsystem. Fixes bug #46272 "MySQL 5.4.4, new MDL: unnecessary deadlock" and bug #37346 "innodb does not detect deadlock between update and alter table". The first bug manifested itself as an unwarranted abort of a transaction with ER_LOCK_DEADLOCK error by a concurrent ALTER statement, when this transaction tried to repeat use of a table, which it has already used in a similar fashion before ALTER started. The second bug showed up as a deadlock between table-level locks and InnoDB row locks, which was "detected" only after innodb_lock_wait_timeout timeout. A transaction would start using the table and modify a few rows. Then ALTER TABLE would come in, and start copying rows into a temporary table. Eventually it would stumble on the modified records and get blocked on a row lock. The first transaction would try to do more updates, and get blocked on thr_lock.c lock. This situation of circular wait would only get resolved by a timeout. Both these bugs stemmed from inadequate solutions to the problem of deadlocks occurring between different locking subsystems. In the first case we tried to avoid deadlocks between metadata locking and table-level locking subsystems, when upgrading shared metadata lock to exclusive one. Transactions holding the shared lock on the table and waiting for some table-level lock used to be aborted too aggressively. We also allowed ALTER TABLE to start in presence of transactions that modify the subject table. ALTER TABLE acquires TL_WRITE_ALLOW_READ lock at start, and that block all writes against the table (naturally, we don't want any writes to be lost when switching the old and the new table). TL_WRITE_ALLOW_READ lock, in turn, would block the started transaction on thr_lock.c lock, should they do more updates. This, again, lead to the need to abort such transactions. The second bug occurred simply because we didn't have any mechanism to detect deadlocks between the table-level locks in thr_lock.c and row-level locks in InnoDB, other than innodb_lock_wait_timeout. This patch solves both these problems by moving lock conflicts which are causing these deadlocks into the metadata locking subsystem, thus making it possible to avoid or detect such deadlocks inside MDL. To do this we introduce new type-of-operation-aware metadata locks, which allow MDL subsystem to know not only the fact that transaction has used or is going to use some object but also what kind of operation it has carried out or going to carry out on the object. This, along with the addition of a special kind of upgradable metadata lock, allows ALTER TABLE to wait until all transactions which has updated the table to go away. This solves the second issue. Another special type of upgradable metadata lock is acquired by LOCK TABLE WRITE. This second lock type allows to solve the first issue, since abortion of table-level locks in event of DDL under LOCK TABLES becomes also unnecessary. Below follows the list of incompatible changes introduced by this patch: - From now on, ALTER TABLE and CREATE/DROP TRIGGER SQL (i.e. those statements that acquire TL_WRITE_ALLOW_READ lock) wait for all transactions which has *updated* the table to complete. - From now on, LOCK TABLES ... WRITE, REPAIR/OPTIMIZE TABLE (i.e. all statements which acquire TL_WRITE table-level lock) wait for all transaction which *updated or read* from the table to complete. As a consequence, innodb_table_locks=0 option no longer applies to LOCK TABLES ... WRITE. - DROP DATABASE, DROP TABLE, RENAME TABLE no longer abort statements or transactions which use tables being dropped or renamed, and instead wait for these transactions to complete. - Since LOCK TABLES WRITE now takes a special metadata lock, not compatible with with reads or writes against the subject table and transaction-wide, thr_lock.c deadlock avoidance algorithm that used to ensure absence of deadlocks between LOCK TABLES WRITE and other statements is no longer sufficient, even for MyISAM. The wait-for graph based deadlock detector of MDL subsystem may sometimes be necessary and is involved. This may lead to ER_LOCK_DEADLOCK error produced for multi-statement transactions even if these only use MyISAM: session 1: session 2: begin; update t1 ... lock table t2 write, t1 write; -- gets a lock on t2, blocks on t1 update t2 ... (ER_LOCK_DEADLOCK) - Finally, support of LOW_PRIORITY option for LOCK TABLES ... WRITE was abandoned. LOCK TABLE ... LOW_PRIORITY WRITE from now on has the same priority as the usual LOCK TABLE ... WRITE. SELECT HIGH PRIORITY no longer trumps LOCK TABLE ... WRITE in the wait queue. - We do not take upgradable metadata locks on implicitly locked tables. So if one has, say, a view v1 that uses table t1, and issues: LOCK TABLE v1 WRITE; FLUSH TABLE t1; -- (or just 'FLUSH TABLES'), an error is produced. In order to be able to perform DDL on a table under LOCK TABLES, the table must be locked explicitly in the LOCK TABLES list.
This commit is contained in:
Dmitry Lenev
@ -732,7 +732,31 @@ connection default;
|
||||
--disable_warnings
|
||||
drop table if exists t1;
|
||||
--enable_warnings
|
||||
create table t1 (a int, key a (a));
|
||||
--echo # First test case which is supposed trigger the execution
|
||||
--echo # path on which problem was discovered.
|
||||
create table t1 (a int);
|
||||
insert into t1 values (1);
|
||||
handler t1 open;
|
||||
connection con1;
|
||||
lock table t1 write;
|
||||
send alter table t1 engine=memory;
|
||||
connection con2;
|
||||
let $wait_condition=
|
||||
select count(*) = 1 from information_schema.processlist
|
||||
where state = "Waiting for table" and info = "alter table t1 engine=memory";
|
||||
--source include/wait_condition.inc
|
||||
connection default;
|
||||
--error ER_ILLEGAL_HA
|
||||
handler t1 read a next;
|
||||
handler t1 close;
|
||||
connection con1;
|
||||
--reap
|
||||
unlock tables;
|
||||
drop table t1;
|
||||
--echo # Now test case which was reported originally but which no longer
|
||||
--echo # triggers execution path which has caused the problem.
|
||||
connection default;
|
||||
create table t1 (a int, key(a));
|
||||
insert into t1 values (1);
|
||||
handler t1 open;
|
||||
connection con1;
|
||||
@ -743,10 +767,13 @@ let $wait_condition=
|
||||
where state = "Waiting for table" and info = "alter table t1 engine=memory";
|
||||
--source include/wait_condition.inc
|
||||
connection default;
|
||||
--echo # Since S metadata lock was already acquired at HANDLER OPEN time
|
||||
--echo # and TL_READ lock requested by HANDLER READ is compatible with
|
||||
--echo # ALTER's TL_WRITE_ALLOW_READ the below statement should succeed
|
||||
--echo # without waiting. The old version of table should be used in it.
|
||||
handler t1 read a next;
|
||||
handler t1 close;
|
||||
connection con1;
|
||||
--reap
|
||||
drop table t1;
|
||||
disconnect con1;
|
||||
--source include/wait_until_disconnected.inc
|
||||
@ -1228,15 +1255,27 @@ create table t2 like t1;
|
||||
handler t1 open;
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
lock table t2 read;
|
||||
lock table t1 write, t2 write;
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
send drop table t2;
|
||||
--echo # --> connection con2
|
||||
connection con2;
|
||||
--echo # Waiting for 'drop table t2' to get blocked...
|
||||
let $wait_condition=select count(*)=1 from information_schema.processlist where state='Waiting for table' and info='drop table t2';
|
||||
--source include/wait_condition.inc
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
--error ER_LOCK_DEADLOCK
|
||||
drop table t2;
|
||||
--error ER_LOCK_DEADLOCK
|
||||
rename table t2 to t3;
|
||||
drop table t1;
|
||||
unlock tables;
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
reap;
|
||||
|
||||
--echo # Demonstrate that there is no deadlock with FLUSH TABLE,
|
||||
--echo # even though it is waiting for the other table to go away
|
||||
create table t2 like t1;
|
||||
--echo # Sending:
|
||||
--send flush table t2
|
||||
--echo # --> connection con2
|
||||
@ -1256,6 +1295,7 @@ drop table t2;
|
||||
--echo # lead to deadlocks
|
||||
--echo #
|
||||
create table t1 (a int, key a(a));
|
||||
insert into t1 values (1), (2);
|
||||
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
@ -1265,7 +1305,31 @@ handler t1 open;
|
||||
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
lock tables t1 write;
|
||||
--echo # Sending:
|
||||
--send lock tables t1 write
|
||||
|
||||
--echo # --> connection con2
|
||||
connection con2;
|
||||
--echo # Check that 'lock tables t1 write' waits until transaction which
|
||||
--echo # has read from the table commits.
|
||||
let $wait_condition=
|
||||
select count(*) = 1 from information_schema.processlist
|
||||
where state = "Waiting for table" and info = "lock tables t1 write";
|
||||
--source include/wait_condition.inc
|
||||
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
--echo # The below 'handler t1 read ...' should not be blocked as
|
||||
--echo # 'lock tables t1 write' has not succeeded yet.
|
||||
handler t1 read a next;
|
||||
|
||||
--echo # Unblock 'lock tables t1 write'.
|
||||
commit;
|
||||
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
--echo # Reap 'lock tables t1 write'.
|
||||
--reap
|
||||
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
@ -1279,29 +1343,18 @@ let $wait_condition=
|
||||
select count(*) = 1 from information_schema.processlist
|
||||
where state = "Table lock" and info = "handler t1 read a next";
|
||||
--source include/wait_condition.inc
|
||||
--echo # Sending:
|
||||
--send drop table t1
|
||||
|
||||
--echo # --> connection con2
|
||||
connection con2;
|
||||
--echo # Waiting for 'drop table t1' to get blocked...
|
||||
let $wait_condition=
|
||||
select count(*) = 1 from information_schema.processlist
|
||||
where state = "Waiting for table" and info = "drop table t1";
|
||||
--source include/wait_condition.inc
|
||||
--echo # The below 'drop table t1' should be able to proceed without
|
||||
--echo # waiting as it will force HANDLER to be closed.
|
||||
drop table t1;
|
||||
unlock tables;
|
||||
|
||||
--echo # --> connection default
|
||||
connection default;
|
||||
--echo # Reaping 'handler t1 read a next'...
|
||||
--error ER_LOCK_DEADLOCK
|
||||
--error ER_NO_SUCH_TABLE
|
||||
--reap
|
||||
handler t1 close;
|
||||
commit;
|
||||
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
--echo # Reaping 'drop table t1'...
|
||||
--reap
|
||||
|
||||
--echo # --> connection con1
|
||||
connection con1;
|
||||
@ -1357,3 +1410,84 @@ rename table t4 to t5, t3 to t4, t5 to t3;
|
||||
handler t1 read first;
|
||||
handler t2 read first;
|
||||
drop table t1, t2, t3, t4;
|
||||
|
||||
--echo #
|
||||
--echo # A test for FLUSH TABLES WITH READ LOCK and HANDLER statements.
|
||||
--echo #
|
||||
set autocommit=0;
|
||||
create table t1 (a int, b int, key a (a));
|
||||
insert into t1 (a, b) values (1, 1), (2, 1), (3, 2), (4, 2), (5, 5);
|
||||
create table t2 like t1;
|
||||
insert into t2 (a, b) select a, b from t1;
|
||||
create table t3 like t1;
|
||||
insert into t3 (a, b) select a, b from t1;
|
||||
commit;
|
||||
flush tables with read lock;
|
||||
handler t1 open;
|
||||
lock table t1 read;
|
||||
--error ER_LOCK_OR_ACTIVE_TRANSACTION
|
||||
handler t1 read next;
|
||||
--echo # This implicitly leaves LOCK TABLES but doesn't drop the GLR
|
||||
--error ER_NO_SUCH_TABLE
|
||||
lock table not_exists_write read;
|
||||
--echo # We still have the read lock.
|
||||
--error ER_CANT_UPDATE_WITH_READLOCK
|
||||
drop table t1;
|
||||
handler t1 open;
|
||||
select a from t2;
|
||||
handler t1 read next;
|
||||
flush tables with read lock;
|
||||
handler t2 open;
|
||||
flush tables with read lock;
|
||||
handler t1 read next;
|
||||
select a from t3;
|
||||
handler t2 read next;
|
||||
handler t1 close;
|
||||
rollback;
|
||||
handler t2 close;
|
||||
--error ER_CANT_UPDATE_WITH_READLOCK
|
||||
drop table t1;
|
||||
commit;
|
||||
flush tables;
|
||||
--error ER_CANT_UPDATE_WITH_READLOCK
|
||||
drop table t1;
|
||||
unlock tables;
|
||||
drop table t1;
|
||||
set autocommit=default;
|
||||
drop table t2, t3;
|
||||
|
||||
--echo #
|
||||
--echo # HANDLER statement and operation-type aware metadata locks.
|
||||
--echo # Check that when we clone a ticket for HANDLER we downrade
|
||||
--echo # the lock.
|
||||
--echo #
|
||||
--echo # Establish an auxiliary connection con1.
|
||||
connect (con1,localhost,root,,);
|
||||
--echo # -> connection default
|
||||
connection default;
|
||||
create table t1 (a int, b int, key a (a));
|
||||
insert into t1 (a, b) values (1, 1), (2, 1), (3, 2), (4, 2), (5, 5);
|
||||
begin;
|
||||
insert into t1 (a, b) values (6, 6);
|
||||
handler t1 open;
|
||||
handler t1 read a last;
|
||||
insert into t1 (a, b) values (7, 7);
|
||||
handler t1 read a last;
|
||||
commit;
|
||||
--echo # -> connection con1
|
||||
connection con1;
|
||||
--echo # Demonstrate that the HANDLER doesn't hold MDL_SHARED_WRITE.
|
||||
lock table t1 write;
|
||||
unlock tables;
|
||||
--echo # -> connection default
|
||||
connection default;
|
||||
handler t1 read a prev;
|
||||
handler t1 close;
|
||||
--echo # Cleanup.
|
||||
drop table t1;
|
||||
--echo # -> connection con1
|
||||
connection con1;
|
||||
disconnect con1;
|
||||
--source include/wait_until_disconnected.inc
|
||||
--echo # -> connection default
|
||||
connection default;
|
||||
|
||||
Reference in New Issue
Block a user