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-- source include/have_innodb.inc let $initial_timeout=`select @@innodb_lock_wait_timeout`; set global innodb_lock_wait_timeout=42; connect (a,localhost,root,,); connect (b,localhost,root,,); connection a; select @@innodb_lock_wait_timeout; set innodb_lock_wait_timeout=1; select @@innodb_lock_wait_timeout; connection b; let $connection_b_id=`SELECT CONNECTION_ID()`; select @@innodb_lock_wait_timeout; set global innodb_lock_wait_timeout=347; select @@innodb_lock_wait_timeout; set innodb_lock_wait_timeout=10; select @@innodb_lock_wait_timeout; connect (c,localhost,root,,); connection c; select @@innodb_lock_wait_timeout; disconnect c; --source include/wait_until_disconnected.inc connection a; --replace_result $connection_b_id <connection_b_id> eval SET @connection_b_id = $connection_b_id; create table t1(a int primary key)engine=innodb; begin; insert into t1 values(1),(2),(3); connection b; --send select * from t1 for update; # Observation on information_schema.processlist (2010-12 mysql-5.5) # ----------------------------------------------------------------- # As soon as the server started the execution of the # connection a: --send select ... for update # High parallel load could delay this up to two seconds. # and before either # - the innodb_lock_wait_timeout was exceeded # -> connection b reap gets ER_LOCK_WAIT_TIMEOUT # or # - connection a commits, the lock disappears and the statement # of connection b finishes # -> connection b reap gets success + result set # we see within information_schema.processlist for connection b a row # command state info # Query Sending data select * from t1 for update # The highest time value seen was @@innodb_lock_wait_timeout + 1. # Please note that there is unfortunately nothing which says # that we are just waiting for a lock. connection a; # In order to ensure that the execution of # connection b: select * from t1 for update # has really started and is most probably waiting for the lock now we poll on # information_schema.processlist. # Also our current session innodb_lock_wait_timeout of 10 seconds should big # enough to prevent that connection b ends up with getting ER_LOCK_WAIT_TIMEOUT. # let $wait_timeout= 10; let $wait_condition= SELECT COUNT(*) = 1 FROM information_schema.processlist WHERE id = @connection_b_id AND INFO = 'select * from t1 for update'; --source include/wait_condition.inc commit; connection b; reap; connection a; begin; insert into t1 values(4); connection b; set innodb_lock_wait_timeout=3; # 3 seconds should be big enough that the wait routine of connection a will # hit the time span where our next statement is visible within the # information_schema.processlist. --send select * from t1 for update; connection a; # Wait till the execution of the connection b statement was started. let $wait_timeout= 10; let $wait_condition= SELECT COUNT(*) = 1 FROM information_schema.processlist WHERE id = @connection_b_id AND INFO = 'select * from t1 for update'; --source include/wait_condition.inc # Wait till the execution of the connection b statement has ended. let $wait_timeout= 10; let $wait_condition= SELECT COUNT(*) = 1 FROM information_schema.processlist WHERE id = @connection_b_id AND INFO IS NULL; --source include/wait_condition.inc # Give "commit" though this must be too late for the statement of connection b. commit; connection b; --error ER_LOCK_WAIT_TIMEOUT reap; disconnect b; --source include/wait_until_disconnected.inc connection a; disconnect a; --source include/wait_until_disconnected.inc connection default; drop table t1; --replace_result $initial_timeout <initial_timeout> eval set global innodb_lock_wait_timeout=$initial_timeout;