Some of the server implementations don't support dates later
than 2038 due to the internal time type being 32 bit.
Added checks so that the server will refuse dates that cannot
be handled by either throwing an error when setting date at
runtime or by refusing to start or shutting down the server if
the system date cannot be stored in my_time_t.
and .tar.gz, windows vs linux..
On Intel x86 machines index selection by the MySQL query
optimizer could sometimes depend on the compiler version and
optimization flags used to build the server binary.
The problem was a result of a known issue with floating point
calculations on x86: since internal FPU precision (80 bit)
differs from precision used by programs (32-bit float or 64-bit
double), the result of calculating a complex expression may
depend on how FPU registers are allocated by the compiler and
whether intermediate values are spilled from FPU to memory. In
this particular case compiler versions and optimization flags
had an effect on cost calculation when choosing the best index
in best_access_path().
A possible solution to this problem which has already been
implemented in mysql-trunk is to limit FPU internal precision
to 64 bits. So the fix is a backport of the relevant code to
5.1 from mysql-trunk.
configure.in:
Configure check for fpu_control.h
mysql-test/r/explain.result:
Test case for bug #48537.
mysql-test/t/explain.test:
Test case for bug #48537.
sql/mysqld.cc:
Backport of the code to switch FPU on x86 to 64-bit precision.
Bug#53417 my_getwd() makes assumptions on the buffer sizes which not always hold true
The mysys library contains many functions for rewriting file paths. Most of these
functions makes implicit assumptions on the buffer sizes they write to. If a path is put
in my_realpath() it will propagate to my_getwd() which assumes that the buffer holding
the path name is greater than 2. This is not true in cases.
In the special case where a VARBIN_ITEM is passed as argument to the LOAD_FILE function
this can lead to a crash.
This patch fixes the issue by introduce more safe guards agaist buffer overruns.
Iterative patch improvement. Previously committed patch
caused wrong result on Windows. The previous patch also
broke secure_file_priv for symlinks since not all file
paths which must be compared against this variable are
normalized using the same norm.
The server variable opt_secure_file_priv wasn't
normalized properly and caused the operations
LOAD DATA INFILE .. INTO TABLE ..
and
SELECT load_file(..)
to do different interpretations of the
--secure-file-priv option.
The patch moves code to the server initialization
routines so that the path always is normalized
once and only once.
It was also intended that setting the option
to an empty string should be equal to
lifting all previously set restrictions. This
is also fixed by this patch.
mysql-test/r/loaddata.result:
* Removed test code which will currently break the much used --mem feature of mtr.
mysql-test/t/loaddata.test:
* Removed test code which will currently break the much used --mem feature of mtr.
sql/item_strfunc.cc:
* Replaced string comparing code on opt_secure_file_priv with an interface which guarantees that both file paths are normalized using the same norm on all platforms.
sql/mysql_priv.h:
* Added signature for is_secure_file_path()
sql/mysqld.cc:
* New function for checking if a path compatible with the secure path restriction.
* Added initialization of the opt_secure_file_priv variable.
sql/sql_class.cc:
* Replaced string comparing code on opt_secure_file_priv with an interface which guarantees that both file paths are normalized using the same norm on all platforms.
sql/sql_load.cc:
* Replaced string comparing code on opt_secure_file_priv with an interface which guarantees that both file paths are normalized using the same norm on all platforms.
Correcting a patch misstake. The converted file path is placed in 'buff' not in opt_secure_file_priv.
mysql-test/r/loaddata.result:
* Updated test case; Since secure_file_priv now is normalized the previous values are changed.
sql/mysqld.cc:
* Fixed patch misstake
The server variable opt_secure_file_priv wasn't
normalized properly and caused the operations
LOAD DATA INFILE .. INTO TABLE ..
and
SELECT load_file(..)
to do different interpretations of the
--secure-file-priv option.
The patch moves code to the server initialization
routines so that the path always is normalized
once and only once.
It was also intended that setting the option
to an empty string should be equal to
lifting all previously set restrictions. This
is also fixed by this patch.
sql/mysqld.cc:
* If --secure_file_option is an empty string then the option variable
should be unset.
* opt_secure_file_option should be normalized once when the server starts.
sql/sql_load.cc:
* moved variable normalization code to fix_paths()
Repairing MyISAM table with fulltext indexes and low
myisam_sort_buffer_size may crash the server.
Estimation of number of index entries was done incorrectly,
causing further assertion failure or server crash.
Docs note: min value for myisam_sort_buffer_size has been
changed from 4 to 4096.
mysql-test/r/fulltext.result:
A test case for BUG#51866.
mysql-test/r/myisam.result:
Min value for myisam_sort_buffer_size is 4096.
mysql-test/r/variables.result:
Min value for myisam_sort_buffer_size is 4096.
mysql-test/suite/sys_vars/r/myisam_sort_buffer_size_basic_32.result:
Min value for myisam_sort_buffer_size is 4096.
mysql-test/t/fulltext.test:
A test case for BUG#51866.
sql/mysqld.cc:
Min value for myisam_sort_buffer_size is 4096.
storage/myisam/mi_check.c:
When estimating number of index entries for external
fulltext parser, take into account that key_length may
be bigger than myisam_sort_buffer_size. Reuse logic
from _create_index_by_sort(): force MIN_SORT_BUFFER to
be min value for myisam_sort_buffer_size.
Another problem is that ftkey_nr has no other meaning
than serial number of fulltext index starting with 1.
We can't say if this key using built-in or external
parser basing on it's value. In other words we always
entered if-branch for external parser. At this point,
the only way to check if we use default parser is to
compare keyinfo::parser with &ft_default_parser.
storage/myisam/sort.c:
Get rid of MIN_SORT_MEMORY, use MIN_SORT_BUFFER instead
(defined in myisamdef.h, has the same value and purpose).
This patch fixes some typos and poorly formulated sentences in
the output from mysqld --help --verbose.
Some of the problems described in the bug report are already
handled by the patch for Bug#49447, and are therefore not
included in this patch.
A client doing multiple mysql_library_init() and
mysql_library_end() calls over the lifetime of the process may
experience lost character set data, potentially even a
SIGSEGV.
This patch reinstates the reloading of character set data when
a mysql_library_init() is done after a mysql_library_end().
backporting of bug@30703 to 5.1.
The fixes are backed up with a regression test.
mysql-test/include/test_fieldsize.inc:
waiting to stop is to be actually exclusively for SQL thread.
mysql-test/suite/rpl/r/rpl_show_slave_running.result:
new results file is added.
mysql-test/suite/rpl/t/rpl_show_slave_running.test:
regression test for bug#30703 is added.
sql/mysqld.cc:
refining `show status like slave_running' handler to correspond to one of
`show slave status'.
sql/slave.cc:
A dbug-sync point is added to complement the regression test.
The problem was that the dbug facility was being used after the
per-thread dbug state had already been finalized. The was present
in a few functions which invoked decrement_handler_count, which
in turn invokes my_thread_end on Windows. In my_thread_end, the
per-thread dbug state is finalized. Any use after the state is
finalized ends up creating a new state.
The solution is to process the exit of a function before the
decrement_handler_count function is called.
sql/mysqld.cc:
Process the function exit before decrement_handler_count is
called, as it can end the per-thread dbug state on Windows.
--default-character-set and --character-set-server such
that only the first will give a deprecation warning.
Apart from that, the two options should do the same.
WL#5182 is a follow-up to WL#5154, deprecating a few more options
and system variables.
client/client_priv.h:
The warning message has been changed to not include
a specific version number in the text.
client/mysql.cc:
--no-tee is deprecated
client/mysqldump.c:
--all is deprecated
-a now points to create-options
mysql-test/r/mysqlbinlog.result:
Warning text changed
mysql-test/suite/rpl/r/rpl_row_mysqlbinlog.result:
Warning text changed
sql/mysql_priv.h:
The warning message has been changed to not include
a specific version number in the text.
sql/mysqld.cc:
--use-symbolic-links is deprecated
-s now points to --symbolic-links
--warnings is deprecated
-W now points to --log-warnings
myisam_max_extra_sort_file_size is deprecated
record_buffer is deprecated
--log-update is deprecated
--sql-bin-update-same is deprecated
--skip-locking is deprecated
--skip-symlink is deprecated
--enable-locking is deprecated
--delay-key-write-for-all-tables is deprecated
Several items said to be deprecated in the 4.1 manual
have never been removed. This worklog adds deprecation
warnings when these items are used, and warns the user
that the items will be removed in MySQL 5.6.
A couple of previously deprecation decision have been
reversed (see single file comments)
client/client_priv.h:
Macro similar to the one in the server (mysql_priv.h)
for printing a deprecation warning message
client/mysql.cc:
no-auto-rehash will not be deprecated
skip-line-numbers will not be deprecated
skip-column-names will not be deprecated
no-pager is deprecated
set-variable is deprecated
no-named-commands is deprecated
client/mysqladmin.cc:
set-variable is deprecated
client/mysqlbinlog.cc:
position is deprecated
client/mysqldump.c:
first-slave is deprecated
no-set-names is deprecated
set-variable is deprecated
mysql-test/r/mysqlbinlog.result:
Adding the [Warning] to the test case, just to show that the
deprecation works.
The test case will be changed in Celosia to use --start-position.
mysys/my_getopt.c:
set-variable (include -O) is deprecated
scripts/mysqld_multi.sh:
Warning for mysqld_multi
sql/mysqld.cc:
default-collation is deprecated
log-bin-trust-routine-creators is deprecated
set-variable is deprecated
default-character-set is deprecated
safe-show-database is deprecated
sql/share/errmsg.txt:
Added version number for sql_log_update deprecation message.
It is well-known that due to concurrency issues, a slave can become
inconsistent when a transaction contains updates to both transaction and
non-transactional tables in statement and mixed modes.
In a nutshell, the current code-base tries to preserve causality among the
statements by writing non-transactional statements to the txn-cache which
is flushed upon commit. However, modifications done to non-transactional
tables on behalf of a transaction become immediately visible to other
connections but may not immediately get into the binary log and therefore
consistency may be broken.
In general, it is impossible to automatically detect causality/dependency
among statements by just analyzing the statements sent to the server. This
happen because dependency may be hidden in the application code and it is
necessary to know a priori all the statements processed in the context of
a transaction such as in a procedure. Moreover, even for the few cases that
we could automatically address in the server, the computation effort
required could make the approach infeasible.
So, in this patch we introduce the option
- "--binlog-direct-non-transactional-updates" that can be used to bypass
the current behavior in order to write directly to binary log statements
that change non-transactional tables.
mysql-test/extra/rpl_tests/rpl_mixing_engines.inc:
Backported this from Celosia to improve the test cases related to the NTM issue.
sql/log.cc:
Checks the --binlog-direct-non-transactional-updates before choosing
to either use the trxn-cache or not.
sql/mysqld.cc:
Introduces the option --binlog-direct-non-transactional-updates.
sql/set_var.cc:
Introduces the option --binlog-direct-non-transactional-updates.
sql/sql_class.h:
Introduces the option --binlog-direct-non-transactional-updates.
When compressed myisam files are opened, they are always memory mapped
sometimes causing memory swapping problems.
When we mmap the myisam compressed tables of size greater than the memory
available, the kswapd0 process utilization is very high consuming 30-40% of
the cpu. This happens only with linux kernels older than 2.6.9
With newer linux kernels, we don't have this problem of high cpu consumption
and this option may not be required.
The option 'myisam_mmap_size' is added to limit the amount of memory used for
memory mapping of myisam files. This option is not dynamic.
The default value on 32 bit system is 4294967295 bytes and on 64 bit system it
is 18446744073709547520 bytes.
Note: Testcase only tests the option variable. The actual bug has be to
tested manually.
include/my_global.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
define SIZE_T_MAX
include/myisam.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
declare 'myisam_mmap_size' and 'myisam_mmap_used' variables and the mutex
THR_LOCK_myisam_mmap
myisam/mi_packrec.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add 'myisam_mmap_size' option which limits the memory available to mmap of
myisam files
myisam/mi_static.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
declare 'myisam_mmap_size' and 'myisam_mmap_used' variables and the mutex
THR_LOCK_myisam_mmap
myisam/myisamdef.h:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
move MEMMAP_EXTRA_MARGIN to myisam.h so that it can be used in mysqld.cc
mysql-test/r/variables.result:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
Testcase for BUG#37408 to test the myisam_mmap_size option
mysql-test/t/variables.test:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
Testcase for BUG#37408 to test the myisam_mmap_size option
mysys/my_thr_init.c:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
intialize the lock THR_LOCK_myisam_mmap
sql/mysqld.cc:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add the 'myisam_mmap_size' option
sql/set_var.cc:
Fix for Bug #37408 - Compressed MyISAM files should not require/use mmap()
add the 'myisam_mmap_size' to the SHOW VARIABLES list
As documented in the bug report, the double checked locking
pattern has inherent issues, and cannot guarantee correct
initialization.
This patch replaces the logic in init_available_charsets()
with the use of pthread_once(3). A wrapper function,
my_pthread_once(), is introduced and is used in lieu of direct
calls to init_available_charsets(). Related defines
MY_PTHREAD_ONCE_* are also introduced.
For the Windows platform, the implementation in lp:sysbench is
ported. For single-thread use, a simple define calls the
function and sets the pthread_once control variable.
Charset initialization is modified to use my_pthread_once().
include/my_no_pthread.h:
Dummy my_pthread_once() for single thread use.
include/my_pthread.h:
Declaration for new function my_pthread_once().
mysys/charset.c:
Logic in init_available_charsets() is simplified.
Using my_pthread_once() for all calls to this func.
mysys/my_winthread.c:
Windows implementation of my_pthread_once().
The help text for --init-slave=name:
"Command(s) that are executed when a slave connects to this master".
This text indicate that the --init-slave option is set on a master
server, and the master server passes the option's argument to slave
which connects to it. This is wrong. Actually the --init-slave option
just can be set on a slave server, and then the slave server executes
the argument each time the SQL thread starts.
Correct the help text for --init-slave option as following:
"Command(s) that are executed by a slave server each time the SQL thread starts."
sql/mysqld.cc:
Correct the help text for --init-slave option.
The help text for --init-slave=name:
"Command(s) that are executed when a slave connects to this master".
This text indicate that the --init-slave option is set on a master
server, and the master server passes the option's argument to slave
which connects to it. This is wrong. Actually the --init-slave option
just can be set on a slave server, and then the slave server executes
the argument each time the SQL thread starts.
Correct the help text for --init-slave option as following:
"Command(s) that are executed by a slave server each time the SQL thread starts."
sql/mysqld.cc:
Correct the help text for --init-slave option.
This patch fixes three bugs as follows. First, aborting the server while purging
binary logs might generate orphan files due to how the purge operation was
implemented:
(purge routine - sql/log.cc - MYSQL_BIN_LOG::purge_logs)
1 - register the files to be removed in a temporary buffer.
2 - update the log-bin.index.
3 - flush the log-bin.index.
4 - erase the files whose names where register in the temporary buffer
in step 1.
Thus a failure while executing step 4 would generate an orphan file. Second,
a similar issue might happen while creating a new binary as follows:
(create routine - sql/log.cc - MYSQL_BIN_LOG::open)
1 - open the new log-bin.
2 - update the log-bin.index.
Thus a failure while executing step 1 would generate an orphan file.
To fix these issues, we record the files to be purged or created before really
removing or adding them. So if a failure happens such records can be used to
automatically remove dangling files. The new steps might be outlined as follows:
(purge routine - sql/log.cc - MYSQL_BIN_LOG::purge_logs)
1 - register the files to be removed in the log-bin.~rec~ placed in
the data directory.
2 - update the log-bin.index.
3 - flush the log-bin.index.
4 - delete the log-bin.~rec~.
(create routine - sql/log.cc - MYSQL_BIN_LOG::open)
1 - register the file to be created in the log-bin.~rec~
placed in the data directory.
2 - open the new log-bin.
3 - update the log-bin.index.
4 - delete the log-bin.~rec~.
(recovery routine - sql/log.cc - MYSQL_BIN_LOG::open_index_file)
1 - open the log-bin.index.
2 - open the log-bin.~rec~.
3 - for each file in log-bin.~rec~.
3.1 Check if the file is in the log-bin.index and if so ignore it.
3.2 Otherwise, delete it.
The third issue can be described as follows. The purge operation was allowing
to remove a file in use thus leading to the loss of data and possible
inconsistencies between the master and slave. Roughly, the routine was only
taking into account the dump threads and so if a slave was not connect the
file might be delete even though it was in use.
implement Davi's review suggestions (post-push fixes)
include/violite.h:
Use official abbreviation for milliseconds (ms)
sql/mysqld.cc:
Fix formatting
Add error handling for the case of CreateEvent error
vio/vio.c:
Use official abbreviation for milliseconds(ms)
Remove superfluous memset
Fix formatting
vio/viosocket.c:
Use official abbreviation for milliseconds (ms)
Use size_t datatype instead of int in pipe_complete_io
If --log-bin is set to a directory name with the trailing 'FN_LIBCHAR',
which will be '/' on Unix like systems, and '\\' on Windows like systems.
the basename of the binlog is empty so that the created files named
'.000001' and '.index'. It is not expected.
The same thing happened to --log-bin-index, --relay-log and
--relay-log-index options.
To resolve the problem, in these cases the program should report an error
and abort.
sql/mysqld.cc:
Added a check for the value of the --log-bin and --log-bin-index arguments,
if it's a directory, reports an error and aborts.
sql/rpl_rli.cc:
Added a check for the value of the --relay-log and --relay-log-index arguments,
if it's a directory, reports an error and aborts.
Bug#31621: Windows server hanging during shutdown using named pipes
and idle connection
Problem: when idle pipe connection is forcefully closed with KILL
statement or when the server goes down, thread that is closing connection
would hang infinitely in CloseHandle(). The reason for the hang is that
named pipe operations are performed synchronously. In this mode all IOs
on pipe are serialized, that is CloseHandle() will not abort ReadFile()
in another thread, but wait for ReadFile() to complete.
The fix implements asynchrnous mode for named pipes, where operation of file
are not synchronized. Read/Write operation would fire an async IO and wait for
either IO completion or timeout.
Note, that with this patch timeouts are properly handled for named pipes.
Post-review: Win32 timeout code has been fixed for named pipes and shared
memory. We do not store pointer to NET in vio structure, only the read and
write timeouts.
include/violite.h:
Add pipe_overlapped to Vio structure for async IO for named pipes.
sql-common/client.c:
Use asynchronous pipe IO.
sql/mysqld.cc:
Use asynchronous pipe IO.
vio/vio.c:
-Refactor timeouts for win32 protocols: shared memory and named pipes.
Store read/write timeout in VIO structure, instead of storing pointer
to NET. New function vio_win32_timeout called indirectly via
vio_timeout changes these values.
vio/vio_priv.h:
Remove vio_ignore_timeout.
Add vio_win32_timeout to be used for named pipes and shared memory.
vio/viosocket.c:
Use async IO for named pipes.
After issuing IO, wait for either IO completion, pipe_close_event
or timeout.
Refactor timeouts for named pipe and shared memory.
Implemented the server infrastructure for the fix:
1. Added a function LEX_STRING *thd_query_string(THD) to return
a LEX_STRING structure instead of char *.
This is the function that must be called in innodb instead of
thd_query()
2. Did some encapsulation in THD : aggregated thd_query and
thd_query_length into a LEX_STRING and made accessor and mutator
methods for easy code updating.
3. Updated the server code to use the new methods where applicable.
Backport from 6.0 to 5.1.
Only those sync points are included, which are used in debug_sync.test.
The Debug Sync Facility allows to place synchronization points
in the code:
open_tables(...)
DEBUG_SYNC(thd, "after_open_tables");
lock_tables(...)
When activated, a sync point can
- Send a signal and/or
- Wait for a signal
Nomenclature:
- signal: A value of a global variable that persists
until overwritten by a new signal. The global
variable can also be seen as a "signal post"
or "flag mast". Then the signal is what is
attached to the "signal post" or "flag mast".
- send a signal: Assign the value (the signal) to the global
variable ("set a flag") and broadcast a
global condition to wake those waiting for
a signal.
- wait for a signal: Loop over waiting for the global condition until
the global value matches the wait-for signal.
Please find more information in the top comment in debug_sync.cc
or in the worklog entry.
.bzrignore:
WL#4259 - Debug Sync Facility
Added the symbolic link libmysqld/debug_sync.cc.
CMakeLists.txt:
WL#4259 - Debug Sync Facility
Added definition for ENABLED_DEBUG_SYNC.
configure.in:
WL#4259 - Debug Sync Facility
Added definition for ENABLED_DEBUG_SYNC.
include/my_sys.h:
WL#4259 - Debug Sync Facility
Added definition for the DEBUG_SYNC_C macro.
libmysqld/CMakeLists.txt:
WL#4259 - Debug Sync Facility
Added sql/debug_sync.cc.
libmysqld/Makefile.am:
WL#4259 - Debug Sync Facility
Added sql/debug_sync.cc.
mysql-test/include/have_debug_sync.inc:
WL#4259 - Debug Sync Facility
New include file.
mysql-test/mysql-test-run.pl:
WL#4259 - Debug Sync Facility
Added option --debug_sync_timeout.
mysql-test/r/debug_sync.result:
WL#4259 - Debug Sync Facility
New test result.
mysql-test/r/have_debug_sync.require:
WL#4259 - Debug Sync Facility
New require file.
mysql-test/t/debug_sync.test:
WL#4259 - Debug Sync Facility
New test file.
mysys/my_static.c:
WL#4259 - Debug Sync Facility
Added definition for debug_sync_C_callback_ptr.
mysys/thr_lock.c:
WL#4259 - Debug Sync Facility
Added sync point "wait_for_lock".
sql/CMakeLists.txt:
WL#4259 - Debug Sync Facility
Added debug_sync.cc and debug_sync.h.
sql/Makefile.am:
WL#4259 - Debug Sync Facility
Added debug_sync.cc and debug_sync.h.
sql/debug_sync.cc:
WL#4259 - Debug Sync Facility
New source file.
sql/debug_sync.h:
WL#4259 - Debug Sync Facility
New header file.
sql/mysqld.cc:
WL#4259 - Debug Sync Facility
Added opt_debug_sync_timeout.
Added calls to debug_sync_init() and debug_sync_end().
Fixed a purecov comment (unrelated).
sql/set_var.cc:
WL#4259 - Debug Sync Facility
Added server variable "debug_sync".
sql/set_var.h:
WL#4259 - Debug Sync Facility
Added declaration for server variable "debug_sync".
sql/share/errmsg.txt:
WL#4259 - Debug Sync Facility
Added error messages ER_DEBUG_SYNC_TIMEOUT and ER_DEBUG_SYNC_HIT_LIMIT.
sql/sql_base.cc:
WL#4259 - Debug Sync Facility
Added sync points "after_flush_unlock" and "before_lock_tables_takes_lock".
sql/sql_class.cc:
WL#4259 - Debug Sync Facility
Added initialization for debug_sync_control to THD::THD.
Added calls to debug_sync_init_thread() and debug_sync_end_thread().
sql/sql_class.h:
WL#4259 - Debug Sync Facility
Added element debug_sync_control to THD.
storage/myisam/myisamchk.c:
Fixed a typo in an error message string (unrelated).
when compiled with Sun Studio compiler).
The thing is that Sun Studio compiler calls destructor of stack
objects when pthread_exit() is called. That triggered an assertion
in DBUG_ENTER()/DBUG_RETURN() validation logic (if DBUG_ENTER() is
used in the beginning of function, all returns should be replaced
by DBUG_RETURN/DBUG_VOID_RETURN macros).
A fix is to explicitly use DBUG_LEAVE macro.
When parsing the service installation parameter in
default_service_handling() make sure the value of the
optional parameter doesn't overwrite it's name.
- Define and pass compile time path variables as pre-processor definitions to
mimic the makefile build.
- Set new CMake version and policy requirements explicitly.
- Changed DATADIR to MYSQL_DATADIR to avoid conflicting definition in
Platform SDK header ObjIdl.h which also defines DATADIR.
Initialize LOCK_open as a adapative mutex on platforms where the
PTHREAD_ADAPTIVE_MUTEX_INITIALIZER_NP macro is available. The flag
indicates that a thread should spin (busy wait) for some time on a
locked adaptive mutex before blocking (sleeping). It's intended to
to alleviate performance problems due to LOCK_open being a highly
contended mutex.
sql/mysqld.cc:
Initialize LOCK_open as a adapative mutex.
