mariadb/sql/event_data_objects.h
Dmitry Lenev 378cdc58c1 Patch that refactors global read lock implementation and fixes
bug #57006 "Deadlock between HANDLER and FLUSH TABLES WITH READ
LOCK" and bug #54673 "It takes too long to get readlock for
'FLUSH TABLES WITH READ LOCK'".

The first bug manifested itself as a deadlock which occurred
when a connection, which had some table open through HANDLER
statement, tried to update some data through DML statement
while another connection tried to execute FLUSH TABLES WITH
READ LOCK concurrently.

What happened was that FTWRL in the second connection managed
to perform first step of GRL acquisition and thus blocked all
upcoming DML. After that it started to wait for table open
through HANDLER statement to be flushed. When the first connection
tried to execute DML it has started to wait for GRL/the second
connection creating deadlock.

The second bug manifested itself as starvation of FLUSH TABLES
WITH READ LOCK statements in cases when there was a constant
stream of concurrent DML statements (in two or more
connections).

This has happened because requests for protection against GRL
which were acquired by DML statements were ignoring presence of
pending GRL and thus the latter was starved.

This patch solves both these problems by re-implementing GRL
using metadata locks.

Similar to the old implementation acquisition of GRL in new
implementation is two-step. During the first step we block
all concurrent DML and DDL statements by acquiring global S
metadata lock (each DML and DDL statement acquires global IX
lock for its duration). During the second step we block commits
by acquiring global S lock in COMMIT namespace (commit code
acquires global IX lock in this namespace).

Note that unlike in old implementation acquisition of
protection against GRL in DML and DDL is semi-automatic.
We assume that any statement which should be blocked by GRL
will either open and acquires write-lock on tables or acquires
metadata locks on objects it is going to modify. For any such
statement global IX metadata lock is automatically acquired
for its duration.

The first problem is solved because waits for GRL become
visible to deadlock detector in metadata locking subsystem
and thus deadlocks like one in the first bug become impossible.

The second problem is solved because global S locks which
are used for GRL implementation are given preference over
IX locks which are acquired by concurrent DML (and we can
switch to fair scheduling in future if needed).

Important change:
FTWRL/GRL no longer blocks DML and DDL on temporary tables.
Before this patch behavior was not consistent in this respect:
in some cases DML/DDL statements on temporary tables were
blocked while in others they were not. Since the main use cases
for FTWRL are various forms of backups and temporary tables are
not preserved during backups we have opted for consistently
allowing DML/DDL on temporary tables during FTWRL/GRL.

Important change:
This patch changes thread state names which are used when
DML/DDL of FTWRL is waiting for global read lock. It is now
either "Waiting for global read lock" or "Waiting for commit
lock" depending on the stage on which FTWRL is.

Incompatible change:
To solve deadlock in events code which was exposed by this
patch we have to replace LOCK_event_metadata mutex with
metadata locks on events. As result we have to prohibit
DDL on events under LOCK TABLES.

This patch also adds extensive test coverage for interaction
of DML/DDL and FTWRL.

Performance of new and old global read lock implementations
in sysbench tests were compared. There were no significant
difference between new and old implementations.
2010-11-11 20:11:05 +03:00

195 lines
3.7 KiB
C++

#ifndef _EVENT_DATA_OBJECTS_H_
#define _EVENT_DATA_OBJECTS_H_
/* Copyright (C) 2004-2006 MySQL AB
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; version 2 of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */
/**
@addtogroup Event_Scheduler
@{
@file event_data_objects.h
*/
#include "event_parse_data.h"
#include "thr_lock.h" /* thr_lock_type */
class Field;
class THD;
class Time_zone;
struct TABLE;
class Event_queue_element_for_exec
{
public:
Event_queue_element_for_exec(){};
~Event_queue_element_for_exec();
bool
init(LEX_STRING dbname, LEX_STRING name);
LEX_STRING dbname;
LEX_STRING name;
bool dropped;
THD *thd;
private:
/* Prevent use of these */
Event_queue_element_for_exec(const Event_queue_element_for_exec &);
void operator=(Event_queue_element_for_exec &);
};
class Event_basic
{
protected:
MEM_ROOT mem_root;
public:
LEX_STRING dbname;
LEX_STRING name;
LEX_STRING definer;// combination of user and host
Time_zone *time_zone;
Event_basic();
virtual ~Event_basic();
virtual bool
load_from_row(THD *thd, TABLE *table) = 0;
protected:
bool
load_string_fields(Field **fields, ...);
bool
load_time_zone(THD *thd, const LEX_STRING tz_name);
};
class Event_queue_element : public Event_basic
{
public:
int on_completion;
int status;
longlong originator;
my_time_t last_executed;
my_time_t execute_at;
my_time_t starts;
my_time_t ends;
my_bool starts_null;
my_bool ends_null;
my_bool execute_at_null;
longlong expression;
interval_type interval;
bool dropped;
uint execution_count;
Event_queue_element();
virtual ~Event_queue_element();
virtual bool
load_from_row(THD *thd, TABLE *table);
bool
compute_next_execution_time();
void
mark_last_executed(THD *thd);
};
class Event_timed : public Event_queue_element
{
Event_timed(const Event_timed &); /* Prevent use of these */
void operator=(Event_timed &);
public:
LEX_STRING body;
LEX_STRING definer_user;
LEX_STRING definer_host;
LEX_STRING comment;
ulonglong created;
ulonglong modified;
ulong sql_mode;
class Stored_program_creation_ctx *creation_ctx;
LEX_STRING body_utf8;
Event_timed();
virtual ~Event_timed();
void
init();
virtual bool
load_from_row(THD *thd, TABLE *table);
int
get_create_event(THD *thd, String *buf);
};
class Event_job_data : public Event_basic
{
public:
LEX_STRING body;
LEX_STRING definer_user;
LEX_STRING definer_host;
ulong sql_mode;
class Stored_program_creation_ctx *creation_ctx;
Event_job_data();
virtual bool
load_from_row(THD *thd, TABLE *table);
bool
execute(THD *thd, bool drop);
private:
bool
construct_sp_sql(THD *thd, String *sp_sql);
bool
construct_drop_event_sql(THD *thd, String *sp_sql);
Event_job_data(const Event_job_data &); /* Prevent use of these */
void operator=(Event_job_data &);
};
/* Compares only the schema part of the identifier */
bool
event_basic_db_equal(LEX_STRING db, Event_basic *et);
/* Compares the whole identifier*/
bool
event_basic_identifier_equal(LEX_STRING db, LEX_STRING name, Event_basic *b);
/**
@} (End of group Event_Scheduler)
*/
#endif /* _EVENT_DATA_OBJECTS_H_ */