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A working Posix thread library is needed for the server. On Solaris 2.5 we use SUN PThreads (the native thread support in 2.4 and earlier versions are not good enough) and on Linux we use LinuxThreads by Xavier Leroy, [email protected].
The hard part of porting to a new Unix variant without good native thread support is probably to port MIT-pthreads. See `mit-pthreads/README' and Programming POSIX Threads.
The MySQL distribution includes a patched version of Provenzano's Pthreads from MIT (see MIT Pthreads web page). This can be used for some operating systems that do not have POSIX threads.
It is also possible to use another user level thread package named FSU Pthreads (see FSU Pthreads home page). This implementation is being used for the SCO port.
See the `thr_lock.c' and `thr_alarm.c' programs in the `mysys' directory for some tests/examples of these problems.
Both the server and the client need a working C++ compiler (we use gcc and
have tried SparcWorks). Another compiler that is known to work is the Irix cc.
To compile only the client use ./configure --without-server.
There is currently no support for only compiling the server. Nor is it likly to be added unless someone has a good reason for it.
If you want/need to change any `Makefile' or the configure script you must get
Automake and Autoconf. We have used the automake-1.2 and autoconf-2.12
distributions.
All steps needed to remake everything from the most basic files.
/bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug --prefix='your installation directory' # The makefiles generated above need GNU make 3.75 or newer. # (called gmake below) gmake clean all install init-db
If you run into problems with a new port, you may have to do some debugging of MySQL! See section G.1 Debugging a MySQL server.
Note: Before you start debugging mysqld, first get the
test programs mysys/thr_alarm and mysys/thr_lock to work. This
will ensure that your thread installation has even a remote chance to work!
If you are using some functionality that is very new in MySQL, you can
try to run mysqld with the --skip-new (which will disable all new,
potentially unsafe functionality) or with --safe-mode which disables a lot of
optimization that may cause problems. See section 18.1
What to do if MySQL keeps crashing.
If mysqld doesn't want to start, you should check that you don't have any my.cnf
file that interferes with your setup! You can check your my.cnf arguments
with mysqld --print-defaults and avoid using them by starting with mysqld
--no-defaults ....
If you have some very specific problem, you can always try to debug MySQL.
To do this you must configure MySQL with the option --with-debug.
You can check whether or not MySQL was compiled with debugging by doing: mysqld
--help. If the --debug flag is listed with the options then you have
debugging enabled. mysqladmin ver also lists the mysqld version
as mysql ... -debug in this case.
If you are using gcc or egcs, the recommended configure line is:
CC=gcc CFLAGS="-O6" CXX=gcc CXXFLAGS="-O6 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-debug
This will avoid problems with the libstdc++ library and with C++ exceptions.
If you can cause the mysqld server to crash quickly, you can try to create
a trace file of this:
Start the mysqld server with a trace log in `/tmp/mysql.trace'.
The log file will get very BIG.
mysqld --debug --log
or you can start it with
mysqld --debug=d,info,error,query,general,where:O,/tmp/mysql.trace
which only prints information with the most interesting tags.
When you configure MySQL for debugging you automatically enable a lot
of extra safety check functions that monitor the health of mysqld. If they
find something ``unexpected,'' an entry will be written to stderr, which safe_mysqld
directs to the error log! This also means that if you are having some unexpected problems
with MySQL and are using a source distribution, the first thing you
should do is to configure MySQL for debugging! (The second thing, of
course, is to send mail to [email protected]
and ask for help. Please use the mysqlbug script for all bug reports or
questions regarding the MySQL version you are using!
On most system you can also start mysqld from gdb to get more
information if mysqld crashes.
With some gdb versions on Linux you must use run --one-thread
if you want to be able to debug mysqld threads. In this case you can only
have one thread active at a time.
If you are using gdb 4.17.x on Linux, you should install a `.gdb' file, with the following information, in your current directory:
set print sevenbit off handle SIGUSR1 nostop noprint handle SIGUSR2 nostop noprint handle SIGWAITING nostop noprint handle SIGLWP nostop noprint handle SIGPIPE nostop handle SIGALRM nostop handle SIGHUP nostop handle SIGTERM nostop noprint
Here follows an example how to debug mysqld:
shell> gdb /usr/local/libexec/mysqld gdb> run ... back # Do this when mysqld crashes info locals up info locals up ... (until you get some information about local variables) quit
Include the above output in a mail generated with mysqlbug and mail this
to [email protected].
If mysqld hangs you can try to use some system tools like strace
or /usr/proc/bin/pstack to examine where mysqld has hanged.
If mysqld starts to eat up CPU or memory or if it ``hangs'', you can use mysqladmin
processlist status to find out if someone is executing some query that takes a long
time. It may be a good idea to run mysqladmin -i10 processlist status in some
window if you are experiencing performance problems or problems when new clients can't
connect.
If mysqld dies or hangs, you should start mysqld with --log.
When mysqld dies again, you can check in the log file for the query that
killed mysqld. Note that before starting mysqld with --log
you should check all your tables with myisamchk. See section 13 Maintaining a MySQL installation.
If you are using a log file, mysqld --log, you should check the 'hostname'
log files, that you can find in the database directory, for any queries that could cause a
problem. Try the command EXPLAIN on all SELECT statements that
takes a long time to ensure that mysqld are using indexes properly. See section 7.22 EXPLAIN syntax (Get information
about a SELECT). You should also test complicated queries that didn't
complete within the mysql command line tool.
If you find the text mysqld restarted in the error log file (normally
named `hostname.err') you have probably found a query that causes mysqld
to fail. If this happens you should check all your tables with myisamchk (see
section 13 Maintaining a MySQL installation),
and test the queries in the MySQL log files if someone doesn't work. If
you find such a query, try first upgrading to the newest MySQL version.
If this doesn't help and you can't find anything in the mysql mail archive,
you should report the bug to [email protected].
Links to mail archives are available at the online MySQL
documentation page.
If you get corrupted tables or if mysqld always fails after some update
commands, you can test if this bug is reproducible by doing the following:
mysqladmin shutdown) myisamchk -s database/*.MYI. Repair any wrong tables
with myisamchk -r database/table.MYI. mysqld with --log-update mysqld server. mysqld server without --log-update
mysql < update-log. The update log is saved
in the MySQL database directory with the name your-hostname.#.
ISAM
code! FTP the tables and the update log to ftp://www.mysql.com/pub/mysql/secret
and we will fix this as soon as possible! The command mysqladmin debug will dump some information about locks in
use, used memory and query usage to the mysql log file. This may help solve some problems.
This command also provides some useful information even if you haven't compiled MySQL
for debugging!
If the problem is that some tables are getting slower and slower you should try to
optimize the table with OPTIMIZE TABLE or myisamchk. See section
13 Maintaining a MySQL installation. You
should also check the slow queries with EXPLAIN.
You should also read the OS-specific section in this manual for problems that may be unique to your environment. See section 4.11 System-specific issues.
If
you are using the Perl DBI interface, you can turn on debugging information
by using the trace method or by setting the DBI_TRACE
environment variable. See section 20.5.2 The DBI
interface.
To be able to debug a MySQL client with the integrated debug package,
you should configure MySQL with --with-debug. See section 4.7.3 Typical configure
options.
Before running a client, you should set the MYSQL_DEBUG
environment variable:
shell> MYSQL_DEBUG=d:t:O,/tmp/client.trace shell> export MYSQL_DEBUG
This causes clients to generate a trace file in `/tmp/client.trace'.
If you have problems with your own client code, you should attempt to connect to the
server and run your query using a client that is known to work. Do this by running mysql
in debugging mode (assuming you have compiled MySQL with debugging on):
shell> mysql --debug=d:t:O,/tmp/client.trace
This will provide useful information in case you mail a bug report. See section 2.3 How to report bugs or problems.
If your client crashes at some 'legal' looking code, you should check that your `mysql.h' include file matches your mysql library file. A very common mistake is to use an old `mysql.h' file from an old MySQL installation with new MySQL library.
I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:
They use old version of a lot of POSIX calls and it is very tedious to make wrappers for all functions. I am inclined to think that it would be easier to change the thread libraries to the newest POSIX specification.
Some wrappers are already written. See `mysys/my_pthread.c' for more info.
At least the following should be changed:
pthread_get_specific should use one argument. sigwait should
take two arguments. A lot of functions (at least pthread_cond_wait, pthread_cond_timedwait)
should return the error code on error. Now they return -1 and set errno.
Another problem is that user-level threads use the ALRM signal and this
aborts a lot of functions (read, write, open...). MySQL
should do a retry on interrupt on all of these but it is not that easy to verify it.
The biggest unsolved problem is the following:
To get thread-level alarms I changed `mysys/thr_alarm.c' to wait between
alarms with pthread_cond_timedwait(), but this aborts with error EINTR.
I tried to debug the thread library as to why this happens, but couldn't find any easy
solution.
If someone wants to try MySQL with RTS threads I suggest the following:
-DHAVE_rts_threads. thr_alarm. thr_alarm. If it runs without any ``warning'', ``error'' or aborted
messages, you are on the right track. Here follows a successful run on Solaris: Main thread: 1 Tread 0 (5) started Thread: 5 Waiting process_alarm Tread 1 (6) started Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 1 (1) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 2 (2) sec Thread: 6 Simulation of no alarm needed Thread: 6 Slept for 0 (3) sec Thread: 6 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 4 (4) sec Thread: 6 Waiting process_alarm thread_alarm Thread: 5 Slept for 10 (10) sec Thread: 5 Waiting process_alarm process_alarm thread_alarm Thread: 6 Slept for 5 (5) sec Thread: 6 Waiting process_alarm process_alarm ... thread_alarm Thread: 5 Slept for 0 (1) sec end
MySQL is very dependent on the thread package used. So when choosing a good platform for MySQL, the thread package is very important.
There are at least three types of thread packages:
ps may
show the different threads. If one thread aborts the whole process aborts. Most system
calls are thread-safe and should require very little overhead. Solaris, HP-UX, AIX and
OSF1 have kernel threads. In some systems kernel threads are managed by integrating user level threads in the system libraries. In such cases, the thread switching can only be done by the thread library and the kernel isn't really ``thread aware''.
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