2.6.1 Linux Notes (All Linux Versions)

The following notes regarding glibc apply only to the situation when you build MySQL yourself. If you are running Linux on an x86 machine, in most cases it is much better for you to just use our binary. We link our binaries against the best patched version of glibc we can come up with and with the best compiler options, in an attempt to make it suitable for a high-load server. So if you read the following text, and are in doubt about what you should do, try our binary first to see if it meets your needs, and worry about your own build only after you have discovered that our binary is not good enough. In that case, we would appreciate a note about it, so we can build a better binary next time. For a typical user, even for setups with a lot of concurrent connections and/or tables exceeding the 2G limit, our binary in most cases is the best choice.MySQL uses LinuxThreads on Linux. If you are using an old Linux version that doesn't have glibc2 , you must install LinuxThreads before trying to compile MySQL. You can get LinuxThreads at http://www.mysql.com/Downloads/Linux/ . Note : we have seen some strange problems with Linux 2.2.14 and MySQL on SMP systems. If you have a SMP system, we recommend you upgrade to Linux 2.4 as soon as possible! Your system will be faster and more stable by doing this!

Note that glibc versions before and including Version 2.1.1 have a fatal bug in pthread_mutex_timedwait handling, which is used when you do INSERT DELAYED . We recommend that you not use INSERT DELAYED before upgrading glibc.

If MySQL can't open enough files, or connections, it may be that you haven't configured Linux to handle enough files.

cat /proc/sys/fs/file-max
cat /proc/sys/fs/dquot-max
cat /proc/sys/fs/super-max

echo 65536 > /proc/sys/fs/file-max
echo 8192 > /proc/sys/fs/dquot-max
echo 1024 > /proc/sys/fs/super-max

Alternatively, you can set these parameters on bootup by using the sysctl tool, which is used by many Linux distributions (SuSE has added it as well, beginning with SuSE Linux 8.0). Just put the following values into a file named /etc/sysctl.conf :

# Increase some values for MySQL
fs.file-max = 65536
fs.dquot-max = 8192
fs.super-max = 1024

[safe_mysqld]
open-files-limit=8192

If you build MySQL yourself and do not want to mess with patching LinuxThreads, you should set max_connections to a value no higher than 500. It should be even less if you have a large key buffer, large heap tables, or some other things that make mysqld allocate a lot of memory, or if you are running a 2.2 kernel with a 2G patch. If you are using our binary or RPM version 3.23.25 or later, you can safely set max_connections at 1500, assuming no large key buffer or heap tables with lots of data. The more you reduce STACK_SIZE in LinuxThreads the more threads you can safely create. We recommend the values between 128K and 256K.

We have tested MySQL on the 2.4 kernel on a 2-CPU machine and found MySQL scales much better-there was virtually no slowdown on queries throughput all the way up to 1000 clients, and the MySQL scaling factor (computed as the ratio of maximum throughput to the throughput with one client) was 180%. We have observed similar results on a 4-CPU system-virtually no slowdown as the number of clients was increased up to 1000, and 300% scaling factor. So for a high-load SMP server we would definitely recommend the 2.4 kernel at this point. We have discovered that it is essential to run mysqld process with the highest possible priority on the 2.4 kernel to achieve maximum performance. This can be done by adding renice -20 $$ command to safe_mysqld . In our testing on a 4-CPU machine, increasing the priority gave 60% increase in throughput with 400 clients.

We recommend that you use the above patches to build a special static version of libpthread.a and use it only for statically linking against MySQL . We know that the patches are safe for MySQL and significantly improve its performance, but we cannot say anything about other applications. If you link other applications against the patched version of the library, or build a patched shared version and install it on your system, you are doing it at your own risk with regard to other applications that depend on LinuxThreads .

One known problem with the binary distribution is that with older Linux systems that use libc (like RedHat 4.x or Slackware), you will get some non-fatal problems with hostname resolution. Linux Notes for Binary Distributions .

To get a core dump on Linux if mysqld dies with a SIGSEGV signal, you can start mysqld with the --core-file option. Note that you also probably need to raise the core file size by adding ulimit -c 1000000 to safe_mysqld or starting safe_mysqld with --core-file-size=1000000 . safe_mysqld , le script père de mysqld .

ld.so.1: ./my: fatal: libmysqlclient.so.4:
open failed: No such file or directory

• Link the client with the following flag (instead of -Lpath ): -Wl,r/path-libmysqlclient.so .
• Copy libmysqclient.so to /usr/lib .
• Add the pathname of the directory where libmysqlclient.so is located to the LD_RUN_PATH environment variable before running your client.

The following configure line should work with fcc/FCC :

CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE \
-DCONST=const -DNO_STRTOLL_PROTO" CXX=FCC CXXFLAGS="-O -K fast -K lib \
-K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE -DCONST=const \
-Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO \
'-D_EXTERN_INLINE=static __inline'" ./configure --prefix=/usr/local/mysql \
--enable-assembler --with-mysqld-ldflags=-all-static --disable-shared \
--with-low-memory

Sommaire :

• Notes relatives à Linux pour les distributions binaires
• Notes relatives à Linux x86
• Notes relatives à Linux SPARC
• Notes relatives à Linux Alpha
• Note relative à Linux PowerPC
• Notes relatives à Linux MIPS
• Notes relatives à Linux IA64