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without FOR UPDATE is causing a lock". SELECT statements with subqueries referencing InnoDB tables were acquiring shared locks on rows in these tables when they were executed in REPEATABLE-READ mode and with statement or mixed mode binary logging turned on. This was a regression which were introduced when fixing bug 39843. The problem was that for tables belonging to subqueries parser set TL_READ_DEFAULT as a lock type. In cases when statement/mixed binary logging at open_tables() time this type of lock was converted to TL_READ_NO_INSERT lock at open_tables() time and caused InnoDB engine to acquire shared locks on reads from these tables. Although in some cases such behavior was correct (e.g. for subqueries in DELETE) in case of SELECT it has caused unnecessary locking. This patch implements minimal version of the fix for the specific problem described in the bug-report which supposed to be not too risky for pushing into 5.1 tree. The 5.5 tree already contains a more appropriate solution which also addresses other related issues like bug 53921 "Wrong locks for SELECTs used stored functions may lead to broken SBR". This patch tries to solve the problem by ensuring that TL_READ_DEFAULT lock which is set in the parser for tables participating in subqueries at open_tables() time is interpreted as TL_READ_NO_INSERT or TL_READ. TL_READ is used only if we know that this is a SELECT and that this particular table is not used by a stored function. Test coverage is added for both InnoDB and MyISAM. This patch introduces an "incompatible" change in locking scheme for subqueries used in SELECT ... FOR UPDATE and SELECT .. IN SHARE MODE. In 4.1 (as well as in 5.0 and 5.1 before fix for bug 39843) the server would use a snapshot InnoDB read for subqueries in SELECT FOR UPDATE and SELECT .. IN SHARE MODE statements, regardless of whether the binary log is on or off. If the user required a different type of read (i.e. locking read), he/she could request so explicitly by providing FOR UPDATE/IN SHARE MODE clause for each individual subquery. The patch for bug 39843 broke this behaviour (which was not documented or tested), and started to use locking reads for all subqueries in SELECT ... FOR UPDATE/IN SHARE MODE. This patch restores 4.1 behaviour. This patch should be mostly null-merged into 5.5 tree.
61 lines
1.4 KiB
PHP
61 lines
1.4 KiB
PHP
#
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# SUMMARY
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# Check if statement reading table '$table' takes shared locks
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# on some of its rows.
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#
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# PARAMETERS
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# $table Table for which presence of row locks should be checked.
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# $con_aux Name of auxiliary connection to be used by this script.
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# $statement Statement to be checked.
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# $wait_statement Sub-statement which is supposed to acquire locks (should
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# be the same as $statement for ordinary statements).
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#
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# EXAMPLE
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# innodb_mysql_lock2.test
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#
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--disable_result_log
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--disable_query_log
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connection default;
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begin;
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--eval select * from $table for update;
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connection $con_aux;
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begin;
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--send_eval $statement;
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--enable_result_log
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--enable_query_log
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connection default;
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# Wait until statement is successfully blocked because
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# all rows in table are X-locked. This means that at
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# least it acquires S-locks on some of rows.
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let $wait_condition=
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select count(*) = 1 from information_schema.processlist
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where state in ("Sending data","statistics", "preparing") and
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info = "$wait_statement";
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--source include/wait_condition.inc
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--disable_result_log
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--disable_query_log
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rollback;
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connection $con_aux;
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--reap
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rollback;
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connection default;
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--enable_result_log
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--enable_query_log
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if ($success)
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{
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--echo Success: '$statement' takes shared row locks on '$table'.
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}
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if (!$success)
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{
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--echo Error: '$statement' hasn't taken shared row locks on '$table'!
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}
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