SHOW PROCESSLIST, SHOW BINLOGS
Problem: A deadlock was occurring when 4 threads were
involved in acquiring locks in the following way
Thread 1: Dump thread ( Slave is reconnecting, so on
Master, a new dump thread is trying kill
zombie dump threads. It acquired thread's
LOCK_thd_data and it is about to acquire
mysys_var->current_mutex ( which LOCK_log)
Thread 2: Application thread is executing show binlogs and
acquired LOCK_log and it is about to acquire
LOCK_index.
Thread 3: Application thread is executing Purge binary logs
and acquired LOCK_index and it is about to
acquire LOCK_thread_count.
Thread 4: Application thread is executing show processlist
and acquired LOCK_thread_count and it is
about to acquire zombie dump thread's
LOCK_thd_data.
Deadlock Cycle:
Thread 1 -> Thread 2 -> Thread 3-> Thread 4 ->Thread 1
The same above deadlock was observed even when thread 4 is
executing 'SELECT * FROM information_schema.processlist' command and
acquired LOCK_thread_count and it is about to acquire zombie
dump thread's LOCK_thd_data.
Analysis:
There are four locks involved in the deadlock. LOCK_log,
LOCK_thread_count, LOCK_index and LOCK_thd_data.
LOCK_log, LOCK_thread_count, LOCK_index are global mutexes
where as LOCK_thd_data is local to a thread.
We can divide these four locks in two groups.
Group 1 consists of LOCK_log and LOCK_index and the order
should be LOCK_log followed by LOCK_index.
Group 2 consists of other two mutexes
LOCK_thread_count, LOCK_thd_data and the order should
be LOCK_thread_count followed by LOCK_thd_data.
Unfortunately, there is no specific predefined lock order defined
to follow in the MySQL system when it comes to locks across these
two groups. In the above problematic example,
there is no problem in the way we are acquiring the locks
if you see each thread individually.
But If you combine all 4 threads, they end up in a deadlock.
Fix:
Since everything seems to be fine in the way threads are taking locks,
In this patch We are changing the duration of the locks in Thread 4
to break the deadlock. i.e., before the patch, Thread 4
('show processlist' command) mysqld_list_processes()
function acquires LOCK_thread_count for the complete duration
of the function and it also acquires/releases
each thread's LOCK_thd_data.
LOCK_thread_count is used to protect addition and
deletion of threads in global threads list. While show
process list is looping through all the existing threads,
it will be a problem if a thread is exited but there is no problem
if a new thread is added to the system. Hence a new mutex is
introduced "LOCK_thd_remove" which will protect deletion
of a thread from global threads list. All threads which are
getting exited should acquire LOCK_thd_remove
followed by LOCK_thread_count. (It should take LOCK_thread_count
also because other places of the code still thinks that exit thread
is protected with LOCK_thread_count. In this fix, we are changing
only 'show process list' query logic )
(Eg: unlink_thd logic will be protected with
LOCK_thd_remove).
Logic of mysqld_list_processes(or file_schema_processlist)
will now be protected with 'LOCK_thd_remove' instead of
'LOCK_thread_count'.
Now the new locking order after this patch is:
LOCK_thd_remove -> LOCK_thd_data -> LOCK_log ->
LOCK_index -> LOCK_thread_count
INTO CLIENT_ERRORS ARRAY
Analysis:
--------
The client may crash while executing a statement due to
the missing mapping of the server error to it's equivalent
client error.
When trying to reallocate memory for the packet buffer, if
the system is out of memory or the packet buffer is large,
the server errors 'ER_OUT_OF_RESOURCES' or 'ER_PACKET_TOO_LARGE'
is returned respectively. The client error number calculated is
negative and when trying to dereference the array of client
error messages with the calculated error number, the client
crashes.
Fix:
----
Map the server error returned to it's equivalent client error
prior to dereferencing the array of client error messages.
Note: Test case is not added since it is difficult to simulate
the error condition.
Description: A typo in create_tailoring() causes the "contraction_flags" to be written
into cs->contractions in the wrong place. This causes two problems:
(1) Anyone relying on `contraction_flags` to decide "could this character be
part of a contraction" is 100% broken.
(2) Anyone relying on `contractions` to determine the weight of a contraction
is mostly broken
Analysis: When we are preparing the contraction in create_tailoring(), we are corrupting the
cs->contractions memory location which is supposed to store the weights(8k) + contraction information(256 bytes). We started storing the contraction information after the 4k location. This is because of logic flaw in the code.
Fix: When we create the contractions, we need to calculate the contraction with (char*) (cs->contractions + 0x40*0x40) from ((char*) cs->contractions) + 0x40*0x40. This makes the "cs->contractions" to move to 8k bytes and stores the contraction information from there. Similarly when we are calculating it for like range queries we need to calculate it from the 8k bytes onwards, this can be done by changing the logic to (const char*) (cs->contractions + 0x40*0x40). And for ucs2 charsets we need to modify the my_cs_can_be_contraction_head() and my_cs_can_be_contraction_tail() to point to 8k+ locations.
The pthread_cond_timedwait(3P) api
uses a const struct timespec for parameter 3.
The instrumentation api for the same, mysql_cond_timedwait,
which expands to inline_mysql_cond_timedwait,
should also take a const parameter for the timespec.
This fix add the missing const to inline_mysql_cond_timedwait.
--Implemented CHECK TABLE...QUICK.
Introduce CHECK TABLE...QUICK that would skip the btr_validate_index()
and btr_search_validate() call, and count the no. of records in each index.
Approved by Marko and Kevin. (rb#3567).
Backport to 5.5
(external Bug#69407 Build warnings with mysql)
support-files/build-tags:
Run etags on sql_yacc.yy, ignore other .yy files
unittest/mysys/explain_filename-t.cc:
NO_PLAN seems to fail on some platforms, use the actual number instead.
USING THE PLUGIN INTERFACE.
ISSUE: No support for floating-point plugin
system variables.
SOLUTION: Allowing plugins to define and expose floating-point
system variables of type double. MYSQL_SYSVAR_DOUBLE
and MYSQL_THDVAR_DOUBLE are added.
ISSUE: Fractional part of the def, min, max values of system
variables are ignored.
SOLUTION: Adding functions that are used to store the raw
representation of a double in the raw bits of unsigned
longlong in a way that the binary representation
remains the same.
Problem:If Disk becomes full while writing into the binlog,
then the server instance hangs till someone frees the space.
After user frees up the disk space, mysql server crashes
with an assert (m_status != DA_EMPTY)
Analysis: wait_for_free_space is being called in an
infinite loop i.e., server instance will hang until
someone frees up the space. So there is no need to
set status bit in diagnostic area.
Fix: Replace my_error/my_printf_error with
sql_print_warning() which prints the warning in error log.
include/my_sys.h:
Provision to call sql_print_warning from mysys files
mysys/errors.c:
Replace my_error/my_printf_error with
sql_print_warning() which prints the warning in error log.
mysys/my_error.c:
implementation of my_printf_warning
mysys/my_write.c:
Adding logic to break infinite loop in the simulation
sql/mysqld.cc:
Provision to call sql_print_warning from mysys files
File names with colon are being disallowed because of the Alternate Data
Stream (ADS) feature of NTFS that could be misused. ADS allows data to be
written to alternate streams of a normal file. The data in alternate
streams cannot be seen by normal tools on Windows (explorer, cmd.exe). As
a result someone can use this feature to hide large amount of data in
alternate streams and admins will have no easy way of figuring out the
files that are using that disk space. The fix also disallows ADS in the
scenarios where file name is passed as some dynamic variable.
An important thing about the fix is that it DOES NOT disallow ADS file
names if they are not dynamic (i.e. if the file is created by using some
option that needs local access to the MySQL server, for example error log
file). The reasoning is that if some MySQL option related to files
requires access to the local machine (it is not dynamic), then user can very
well create data in ADS by some other means. This fixes only those scenarios
which can allow users to create data in ADS over the wire.
File names with colon are being disallowed only on Windows. UNIX
(Linux in particular) supports NTFS, but it will not be a common
scenario for someone to configure a NTFS file system to store MySQL
data on Linux.
Changes in file bug11761752-master.opt are needed due to
bug number 15937938.
THREAD POOLING STRESS TEST
PROBLEM:
Connection stress tests which consists of concurrent
kill connections interleaved with mysql ping queries
cause the mysqld server which uses thread pool scheduler
to crash.
FIX:
Killing a connection involves shutdown and close of client
socket and this can cause EPOLLHUP(or EPOLLERR) events to be
to be queued and handled after disarming and cleanup of
of the connection object (THD) is being done.We disarm the
the connection by modifying the epoll mask to zero which
ensure no events come and release the ownership of waiting
thread that collect events and then do the cleanup of THD.
object.As per the linux kernel epoll source code (
http://lxr.linux.no/linux+*/fs/eventpoll.c#L1771), EPOLLHUP
(or EPOLLERR) can't be masked even if we set EPOLL mask
to zero. So we disarm the connection and thus prevent
execution of any query processing handler/queueing to
client ctx. queue by removing the client fd from the epoll
set via EPOLL_CTL_DEL. Also there is a race condition which
involve the following threads:
1) Thread X executing KILL CONNECTION Y and is in THD::awake
and using mysys_var (holding LOCK_thd_data).
2) Thread Y in tp_process_event executing and is being killed.
3) Thread Z receives KILL flag internally and possible call
the tp_thd_cleanup function which set thread session variable
and changing mysys_var.
The fix for the above race is to set thread session variable
under LOCK_thd_data.
We also do not call THD::awake if we found the thread in the
thread list that is to be killed but it's KILL_CONNECTION flag
set thus avoiding any possible concurrent cleanup. This patch
is approved by Mikael Ronstrom via email review.
The use of Thread_iterator did not work on windows (linking problems).
Solution: Change the interface between the thread_pool and the server
to only use simple free functions.
This patch is for 5.5 only (mimicks similar solution in 5.6)
SHOW 2012 INSTEAD OF 2011
* Added a new macro to hold the current year :
COPYRIGHT_NOTICE_CURRENT_YEAR
* Modified ORACLE_WELCOME_COPYRIGHT_NOTICE macro
to take the initial year as parameter and pick
current year from the above mentioned macro.
PROBLEM:
mysql provides a feature where in a session which is
idle for a period specified by the wait_timeout variable
(whose value is in seconds), the session is closed
This feature is not present when we use thread pool.
FIX:
This patch implements the interface functions which is
required to implement the wait_timeout functionality
in the thread pool plugin.
1. Clear text password client plugin disabled by default.
2. Added an environment variable LIBMYSQL_ENABLE_CLEARTEXT_PLUGIN, that
when set to something starting with '1', 'Y' or 'y' will enable the clear
text
plugin for all connections.
3. Added a new mysql_options() option : MYSQL_ENABLE_CLEARTEXT_PLUGIN
that takes an my_bool argument. When the value of the argument is non-zero
the clear text plugin is enabled for this connection only.
4. Added an enable-cleartext-plugin config file option that takes a numeric
argument. If the numeric value of the numeric argument is non-zero the
clear
text plugin is enabled for the connection
5. Added a boolean command line option "--enable_cleartext_plugin" to
mysql, mysqlslap and mysqladmin. When specified it will call mysql_options
with the effect of #3
6. Added a new CLEARTEXT option to the connect command in mysqltest.
When specified it will enable the cleartext plugin for usage.
7. Added test cases and updated existing ones that need the clear text
plugin.
Several fixes :
* sql-common/client.c
Added a validity check of the fields metadata packet sent
by the server.
Now libmysql will check if the length of the data sent by
the server matches what's expected by the protocol before
using the data.
* client/mysqltest.cc
Fixed the error handling code in mysqltest to avoid sending
new commands when the reading the result set failed (and
there are unread data in the pipe).
* sql_common.h + libmysql/libmysql.c + sql-common/client.c
unpack_fields() now generates a proper error when it fails.
Added a new argument to this function to support the error
generation.
* sql/protocol.cc
Added a debug trigger to cause the server to send a NULL
insted of the packet expected by the client for testing
purposes.
There are two threads. In one thread, dml operation is going on
involving cascaded update operation. In another thread, alter
table add foreign key constraint is happening. Under these
circumstances, it is possible for the dml thread to access a
dict_foreign_t object that has been freed by the ddl thread.
The debug sync test case provides the sequence of operations.
Without fix, the test case will crash the server (because of
newly added assert). With fix, the alter table stmt will return
an error message.
Backporting the fix from MySQL 5.5 to 5.1
rb:961
rb:947
There are two threads. In one thread, dml operation is going on
involving cascaded update operation. In another thread, alter
table add foreign key constraint is happening. Under these
circumstances, it is possible for the dml thread to access a
dict_foreign_t object that has been freed by the ddl thread.
The debug sync test case provides the sequence of operations.
Without fix, the test case will crash the server (because of
newly added assert). With fix, the alter table stmt will return
an error message.
rb:947
approved by Jimmy Yang
On shutdown(), Windows can drop traffic still queued for sending even if that
wasn't specifically requested. As a result, fatal errors (those after
signaling which the server will drop the connection) were sometimes only
seen as "connection lost" on the client side, because the server-side
shutdown() erraneously discarded the correct error message before sending
it.
If on Windows, we now use the Windows API to access the (non-broken) equivalent
of shutdown().
Backport from trunk
On shutdown(), Windows can drop traffic still queued for sending even if that
wasn't specifically requested. As a result, fatal errors (those after
signaling which the server will drop the connection) were sometimes only
seen as "connection lost" on the client side, because the server-side
shutdown() erraneously discarded the correct error message before sending
it.
If on Windows, we now use the Windows API to access the (non-broken) equivalent
of shutdown().
Backport from trunk
include/violite.h:
export mysql_socket_shutdown(). It lives in vio in the backport.
sql/mysqld.cc:
Go through our own shutdown() rather than straight to the POSIX one.
vio/viosocket.c:
Define mysql_socket_shutdown(). On UNIXoid systems, it's just a wrapper for shutdown(), but
on Window, it uses DisconnectEx, which is magic.
ON 64 BIT MACHINES
PROBLEM: When sorting index during repair of
myisam tables, due to improper casting
of buffer size variables value of myisam_
sort_buffer_size is not set greater than
4GB.
SOLUTION: Proper casting of buffer size variable.
myisam_buffer_size changed to unsigned
long long to handle size > 4GB on
linux as well as windows.
Introducing new collations:
utf8_general_mysql500_ci and ucs2_general_mysql500_ci,
to reproduce behaviour of utf8_general_ci and ucs2_general_ci
from mysql-5.1.23 (and earlier).
The collations are added to simplify upgrade from mysql-5.1.23 and earlier.
Note: The patch does not make new server start over old data automatically.
Some manual upgrade procedures are assumed.
Paul: please get in touch with me to discuss upgrade procedures
when documenting this bug.
modified:
include/m_ctype.h
mysql-test/r/ctype_utf8.result
mysql-test/t/ctype_utf8.test
mysys/charset-def.c
strings/ctype-ucs2.c
strings/ctype-utf8.c
