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I 他のシステムへの移植について

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, Xavier.Leroy@inria.fr.

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
./configure --with-debug=full --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! 「I.1 MySQL server のデバッグ」節参照.

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!

I.1 MySQL server のデバッグ

もしあなたが MySQL のとても新しいある機能を使っている場合、 --skip-new (これは全く新しい、潜在的に危険な機能を無効にします) または --safe-mode (これは問題を生じさせるかもしれない多くの最適化を無効にします) オプションで mysqld を実行させることができます。 「21.1.1 MySQL がクラッシュする場合に行うこと」節参照.

もし mysqld が起動しないようなら、 my.cnf が無いかチェックしてください。 my.cnf の引数は mysqld --print-defaults でチェックできます。 また mysqld --no-defaults ... で起動することにより、 my.cnf を無視することが可能です。

もし mysqld が CPU や メモリー を食い始めたり、``ハング'' したりするなら、 mysqladmin processlist status を使用して誰かが多くの時間のかかる クエリを実行しているか確かめることが出来ます。 パフォーマンスの問題や新しいクライアントが接続できないときの問題と もしあなたが考えるなら、 いくつかのウインドウで mysqladmin -i10 processlist status を 実行するのはよい考えでしょう。

mysqladmin debug コマンドは使用中のロック、使用しているメモり、 クエリの使用の情報を、mysql ログファイルにいくつかダンプします これはいくつかの問題解決に役立ちます。 このコマンドは、 MySQL を デバッグ可能でコンパイルしていなくても、いくつかの役立つ情報も提供します。

いくつかのテーブルでだんだん遅くなる問題であるなら、 OPTIMIZE TABLEmyisamchk でテーブルを修復し、最適化を試みるべきです。 遅いクエリは、 EXPLAIN でもチェックできます。 「16 Maintaining a MySQL Installation」節参照.

このマニュアルの OS 固有の問題 の節も読むべきです。 「4.12 System-specific Issues」節参照.

I.1.1 Compiling MYSQL for debugging.

もしあるとても特殊な問題があれば、あなたは、いつも MySQL を デバッグするよう試みることができます。 これを行うには、 MySQL--with-debug オプションか --with-debug=full オプション付きで configure しなくてはなりません。 MySQL がデバッギングを有効にしてコンパイルされているかを 知るには、 mysqld --help とします。 もし --debug フラグが リストされていればデバッグが有効です。 mysqladmin vermysqld のバージョンをリストできます。 この場合は mysql ... -debug と、バージョン番号に表示されるでしょう。

gcc か egcs の場合、推奨する configure のラインは:

CC=gcc CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql --with-debug --with-extra-charsets=complex

これは libstdc++ ライブラリと C++ の例外による問題を避けることが出来るでしょう。 (many compilers have problems with C++ exceptions in threaded code) and compile a MySQL version with support for all character sets.

If you suspect a memory overrun error, you can configure MySQL with --with-debug=full, which will install a memory allocation (SAFEMALLOC) checker. Running with SAFEMALLOC is however quite slow, so if you get performance problems you should start mysqld with the --skip-safemalloc option. This will disable the memory overrun checks for each call to malloc and free.

If mysqld stops crashing when you compile it with --with-debug, you have probably found a compiler bug or a timing bug within MySQL. In this case you can try to add -g to the CFLAGS and CXXFLAGS variables above and not use --with-debug. If mysqld now dies, you can at least attach to it with gdb or use gdb on the core file to find out what happened.

MySQL をデバッグで configure すると、自動で多くの安全な検査関数が enable になります。 これは mysqld の状態をモニターできます。 もしそれら関数がなにか ``予期せぬこと'' を発見したら、それらを stderr に書き出します。 これは safe_mysqld が受け取って error ログに 書き出します! このことはどういうことかというと、 MySQL に予期せぬことが 起きた場合、まず最初にすべきことは、 MySQL をデバッグ有効にして configure することです! (次に、もちろん、 mysql@lists.mysql.com に メールを送り、help を聞くことです。 全てのバグレポート、MySQL のバージョンに 関連する質問は、 mysqlbug スクリプトを使用してください!)

I.1.2 Creating trace files and using gdb on mysqld

もし mysqld サーバーのクラッシュを直に引き起こすことができるなら、 あなたはこのトレースファイルを作成することができます:

mysqld サーバーをトレースログファイル `/tmp/mysqld.trace' オプションで起動。 このログファイルはとても大きくなります。

mysqld --debug --log

mysqld --debug=d,info,error,query,general,where:O,/tmp/mysql.trace


ほとんどのシステムでは、もし mysqld がクラッシュするなら、 gdb から mysqld を起動させて多くの情報を得ることが可能です。

Linux 上でのいくつかの gdb バージョンでは、 mysqld スレッドのデバッグを可能にする場合、 run --one-thread を使用しなくてはなりません。 この場合、一度にただ一つのactiveなスレッドだけを持つことになります。

When running mysqld under gdb, you should disable the stack trace with --skip-stack-trace to be able to catch segfaults within gdb.

It's very hard to debug MySQL under gdb if you do a lot of new connections the whole time as gdb doesn't free the memory for old threads. You can avoid this problem by starting mysqld with -O thread_cache_size= 'max_connections +1'. In most cases just using -O thread_cache_size= 5' will help a lot!

If you want to get a core dump on Linux if mysqld dies with a SIGSEGV signal, you can start mysqld with the --core-file option. This core file can be used to make a backtrace that may help you find out why mysqld died:

shell> gdb mysqld core
gdb>   backtrace
gdb>   info local
gdb>   exit

21.1.1 MySQL がクラッシュする場合に行うこと」節参照.

もし Linux 上で gdb 4.17.x を使用しているなら、 `.gdb' ファイルを いかにしたがって、カレントのディレクトリーにインストールすべきです:

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

If you have problems debugging threads with gdb, you should download gdb 5.x and try this instead. The new gdb version has very improved thread handling!

以下は mysqld のデバッグ例です:

shell> gdb /usr/local/libexec/mysqld
gdb> run
back   # mysqld がクラッシュした際、これを行います
info locals
info locals
(until you get some information about local variables)


上記の出力を、 mysqlbug で作成したメールに含み、 そして mysql@lists.mysql.com. に送ってください。

もし mysqld がハングするなら、 strace/usr/proc/bin/pstack のような システムツールを使用して mysqld がどこでハングしているか 調べることができます。

strace /tmp/log libexec/mysqld

もし Perl DBI を使用しているなら、 trace メソッド、あるいはDBI_TRACE 環境変数で デバッグ情報を有効にできます。 「 The DBI Interface」節参照. 「 The DBI Interface」節参照.

I.1.3 Using a stack trace

On some operating systems, the error log will contain a stack trace if mysqld dies unexpectedly. You can use this to find out where (and maybe why) mysqld died. 「23.1 The Error Log」節参照. To get a stack trace, you should NOT compile mysqld with the -fomit-frame-pointer option to gcc. On Linux-x86 you can use -fomit-frame-pointer -ffixed-ebp to get both speed and a reasonable accurate stack trace. 「I.1.1 Compiling MYSQL for debugging.」節参照.

If the error file contains something like the following:

mysqld got signal 11;
The manual section 'Debugging a MySQL server' tells you how to use a
stack trace and/or the core file to produce a readable backtrace that may
help in finding out why mysqld died
Attemping backtrace. You can use the following information to find out
where mysqld died.  If you see no messages after this, something went
terribly wrong
stack range sanity check, ok, backtrace follows

you can find where mysqld died by doing the following:

  1. Copy the above numbers to a file, for example `mysqld.stack'.
  2. Make a symbol file for the mysqld server:
    nm -n libexec/mysqld > /tmp/mysqld.sym
    Note that many MySQL binary distributions comes with the above file, named mysqld.sym.gz. In this case you must unpack this by doing:
    gunzip < bin/mysqld.sym.gz > /tmp/mysqld.sym
  3. Execute resolve_stack_dump -s /tmp/mysqld.sym -n mysqld.stack. This will print out where mysqld died. If this doesn't help you find out why mysqld died, you should make a bug report and include the output from the above commend with the bug report. Note however that in most cases it will not help us to just have a stack trace to find the reason for the problem. To be able to locate the bug or provide a workaround, we would in most cases need to know the query that killed mysqld and preferable a test case so that we can repeat the problem! 「2.3 バグや問題を報告する方法」節参照.

I.1.4 Using log files to find cause of errors in mysqld

Note that before starting mysqld with --log you should check all your tables with myisamchk. 「16 Maintaining a MySQL Installation」節参照.

もし mysqld が死んだりハングしたりするなら、 mysqld--log で起動すべきです。 再び mysqld が死んだら、 あなたはログファイル中の、 mysqld を kill するクエリをチェックします。

mysqld--log オプションで起動する前に、 全てのテーブルを myisamchk でチェックすべきです。 (前のクラッシュ時にテーブルが壊れているかもしれないので) 「16 Maintaining a MySQL Installation」節参照.

If you are using --log without a file name, the log is stored in the database directory as 'hostname'.log In most cases it's the last query in the log file that killed mysqld, but if possible you should verify this by restarting mysqld and executing the found query from the mysql command line tools. If this works, you should also test all complicated queries that didn't complete.

mysqld が適切にインデックスを使用するのに時間がとてもかかる全ての SELECT 文を EXPLAIN で実行することを試みます。 「7.29 EXPLAIN 構文 (SELECTについての情報を得る)」節参照.

You can find the queries that take a long time to execute by starting mysqld with --log-slow-queries. 「23.5 The Slow Query Log」節参照.

もしエラーログファイル(通常 `hostname.err' という名前)中に mysqld restarted という文があるなら、 mysqld を失敗させるクエリを見つけます。 もしこれが起きるなら、myisamchk ( 「16 Maintaining a MySQL Installation」節参照) で全てのテーブルをチェックし、 MySQL ログファイルにあるそのクエリをテストすべきです。 もしそのようなクエリをみつけたなら、まず最初に最新の MySQL にアップグレード してみてください。 もしそれでもだめで、かつ mysql メーリングリストの アーカイブにもなにも見つけることが出来なかったなら、 mysql@lists.mysql.com に バグレポートを出すべきです。 メーリングリストのアーカイブへのリンクは MySQL documentation page.

If you have started mysqld with --with-myisam-recover, MySQL will automatically check and try to repair MyISAM tables if they are marked as 'not closed properly' or 'crashed'. If this happens, MySQL will write an entry in the hostname.err file 'Warning: Checking table ...' which is followed by Warning: Repairing table if the table needs to be repaired. If you get a lot of these errors, without mysqld having died unexpectedly just before, then something is wrong and needs to be investigated further. 「4.16.4 mysqld コマンド行オプション」節参照.

It's of course not a good sign if mysqld did died unexpectedly, but in this case one shouldn't investigate the Checking table... messages but instead try to find out why mysqld died.

I.1.5 Making a test case when you experience table corruption

もし不正なテーブルをえたり、 mysqld が常にいくつかの update コマンドで 失敗するなら、以下のようにしてこのバグの再現をテストします:

You can also use the script mysql_find_rows to just execute some of the update statements if you want to narrow down the problem.

I.2 Debugging a MySQL client

To be able to debug a MySQL client with the integrated debug package, you should configure MySQL with --with-debug. 「4.7.3 典型的な configure オプション」節参照.

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. 「2.3 バグや問題を報告する方法」節参照.

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.3 The DBUG package.

The MySQL server and most MySQL clients are compiled with the DBUG package originally made by Fred Fish. When one has configured MySQL for debugging, this package makes it possible to get a trace file of what the program is debugging.

One uses the debug package by invoking the program with the --debug="..." or the -#... option.

Most MySQL programs has a default debug string that will be used if you don't specify an option to --debug. The default trace file is usually /tmp/programname.trace on Unix and \programname.trace on windows.

The debug control string is a sequence of colon separated fields as follows:


Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:


The currently recognized flag characters are:

d Enable output from DBUG_<N> macros for the current state. May be followed by a list of keywords which selects output only for the DBUG macros with that keyword. An empty list of keywords implies output for all macros.
D Delay after each debugger output line. The argument is the number of tenths of seconds to delay, subject to machine capabilities. That is, -#D,20 is delay two seconds.
f Limit debugging and/or tracing, and profiling to the list of named functions. Note that a null list will disable all functions. The appropriate "d" or "t" flags must still be given, this flag only limits their actions if they are enabled.
F Identify the source file name for each line of debug or trace output.
i Identify the process with the pid or thread id for each line of debug or trace output.
g Enable profiling. Create a file called 'dbugmon.out' containing information that can be used to profile the program. May be followed by a list of keywords that select profiling only for the functions in that list. A null list implies that all functions are considered.
L Identify the source file line number for each line of debug or trace output.
n Print the current function nesting depth for each line of debug or trace output.
N Number each line of dbug output.
o Redirect the debugger output stream to the specified file. The default output is stderr.
O As O but the file is really flushed between each write. When needed the file is closed and reopened between each write.
p Limit debugger actions to specified processes. A process must be identified with the DBUG_PROCESS macro and match one in the list for debugger actions to occur.
P Print the current process name for each line of debug or trace output.
r When pushing a new state, do not inherit the previous state's function nesting level. Useful when the output is to start at the left margin.
S Do function _sanity(_file_,_line_) at each debugged function until _sanity() returns something that differs from 0. (Mostly used with safemalloc to find memory leaks)
t Enable function call/exit trace lines. May be followed by a list (containing only one modifier) giving a numeric maximum trace level, beyond which no output will occur for either debugging or tracing macros. The default is a compile time option.

Some examples of debug control strings which might appear on a shell command line (the "-#" is typically used to introduce a control string to an application program) are:


In MySQL, common tags to print (with the d option) are: enter,exit,error,warning,info and loop.

I.4 Locking methods

Currently MySQL only supports table locking for ISAM/MyISAM and HEAP tables and page level locking for BDB tables. 「13.2.8 MySQL はどのようにテーブルをロックするか」節参照. With MyISAM tables one can freely mix INSERT and SELECT without locks (Versioning).

Starting in version 3.23.33, you can analyze the table lock contention on your system by checkining Table_locks_waited and Table_locks_immediate environemt variables.

Some database users claim that MySQL cannot support near the number of concurrent users because it lacks row-level locking. This is a may be true for some specific applications, but is' not generally true. As always this depends totally on what the application does and what is the access/update pattern of the data.

Pros for row locking:


Table locks are superior to page level / row level locks in the following cases:

Other options than row / page level locking:

Versioning (like we use in MySQL for concurrent inserts) where you can have one writer at the same time as many readers. This means that the database/table supports different views for the data depending on when one started to access it. Other names for this are time travel, copy on write or copy on demand.

Copy on demand is in many case much better than page or row level locking; The worst case does, however, use much more memory than when using normal locks.

Instead of using row level locks one can use application level locks. (Like get_lock/release_lock in MySQL). This works of course only in well-behaved applications.

In many cases one can do an educated guess which locking type is best for the application but generally it's very hard to say that a given lock type is better than another; Everything depends on the application and different part of the application may require different lock types.

Here are some tips about locking in MySQL:

On web application most applications do lots of selects, very few deletes, updates mainly on keys and inserts in some specific tables. The base MySQL setup is VERY tuned for this.

Concurrent users is not a problem if one doesn't mix updates and selects that needs to examine many rows in the same table.

If one mixes inserts and deletes on the same table then INSERT DELAYED may be of great help.

One can also use LOCK TABLES to speed up things (many updates within a single lock is much faster than updates without locks). Splitting thing to different tables will also helps.

If you get speed problems with the table locks in MySQL, you may be able to solve these to convert some of your tables to BDB tables. 「8.5 BDB or Berkeley_DB Tables」節参照.

The optimization section in the manual covers a lot of different aspects of how to tune ones application. 「13.6 最適化に関するその他の助言」節参照.

I.5 Comments about RTS threads

I have tried to use the RTS thread packages with MySQL but stumbled on the following problems:

They use an 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:

I.6 スレッドパッケージ間の違いは何?

MySQL は使用されるスレッドパッケージに非常に依存しています。 そのため、MySQL に良いプラットフォームを選択する時には、 スレッドパッケージが非常に重要です。


いくつかのシステムでは、カーネルスレッドは、システムライブラリ内で、 ユーザレベルスレッドの統合によって管理されます。 この場合、スレッド切替えはスレッドライブラリによってだけ行なわれ、 カーネルは実際には 'thread aware' ではありません。

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