This appendix will help you port MySQL to other operationg systems. Do check the list of currently supported operating systems first. 「2.2.5 MySQL がサポートする OS」節参照. If you have created a new port of MySQL, please let us know so that we can list it here and on our web site (http://www.mysql.com/), recommending it to other users.
Note: If you create a new port of MySQL, you are free to copy and distribute it under the GPL license, but it does not make you a copyright holder of MySQL.
移植先のシステムには POSIX 仕様のスレッドライブラリが必要となります。 我々は Solaris 2.5 では Sun PThreads (2.4以前でサポートされていたネイティブthreadは良くなかった)を、 Linux では Xavier Leroy, Xavier.Leroy@inria.fr による LinuxThreads を使っています。
良いネイティブスレッドを持たない新種の Unix に移植する場合、 多分もっとも大変な作業は MIT-pthreads を導入する部分です。 `mit-pthreads/README' と http://www.humanfactor.com/pthreads/をご覧下さい。
MySQL の配布ファイルには MIT の Provenzano's Pthreads パッチ済みバージョン (http://www.mit.edu:8001/people/proven/pthreads.htmlをご覧下さい。) が含まれています。 これは POSIX 仕様の Threads を持たない OS に使用可能と思われます。
もう1つのユーザレベル thread パッケージ、FSU Pthreads も使用可能と思われます (http://www.informatik.hu-berlin.de/~mueller/pthreads.htmlをご覧下さい。)。 これはSCOへの移植に使用可能です。
そういった問題に関するテストやサンプルのプログラムを作成する場合には `mysys' ディレクトリの `thr_lock.c' と `thr_alarm.c' 等のプログラムをご覧下さい。
移植にはサーバー、クライアントともに C++ コンパイラを必要とします
(ちなみに我々はgccを使っています。SPARCWorks(C++)は試しました。)。
Irix ccも使用できることが確かめられています。
クライアントしか必要無い場合は./configure --without-serverとコンパイルしてください。
サーバのみコンパイルする方法は今のところありません。必要性が生じるまでは今のままです。
`Makefile' か コンフィギャスクリプトに何らかの変更をする必要が生じたなら
Automake と Autoconf を使わなくてはいけません。
ちなみに、我々は automake-1.2 と autoconf-2.12 を使っています。
変更の手順は全て基本的なファイルからやり直す必要があります。
/bin/rm */.deps/*.P /bin/rm -f config.cache aclocal autoheader aclocal automake autoconf ./configure --with-debug=full --prefix='your installation directory' # 上記手順によって生成されるmakefileファイル群はGNU make 3.75以上 # (以下、gmakeと記述します。)を必要とします。 gmake clean all install init-db
新しい移植で問題が発生すればデバッグの必要が生じる場合もあります。
「E.1 MySQL server のデバッグ」節参照.
Note: mysqldのデバッグを開始する前にmysys/thr_alarmとmysys/thr_clockが動くかどうかチェックしてください。これにより貴方のインストールしたthread環境の動作可能性が多少でもあるのかどうかを確かめることができます。
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。
「A.4.1 What To Do If MySQL Keeps Crashing」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 TABLE か
myisamchk 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。
「4 Database Administration」節参照. You should also
check the slow queries with EXPLAIN.
このマニュアルの OS 固有の問題 の節も読むべきです。 「2.6 Operating System Specific Notes」節参照.
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 を
--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 ver も
mysqld 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
This will avoid problems with the libstdc++ library and with C++
exceptions (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！）
In the Windows MySQL distribution, mysqld.exe is by
default compiled with support for trace files.
If the mysqld server doesn't start or if you can cause the
mysqld server to crash quickly, you can try to create a trace
file to find the problem.
To do this you have to have a mysqld that is compiled for debugging.
You can check this by executing mysqld -V. If the version number
ends with -debug, it's compiled with support for trace files.
Start the mysqld server with a trace log in `/tmp/mysqld.trace'
(or `C:\mysqld.trace' on Windows):
mysqld --debug
On Windows you should also use the --standalone flag to not start
mysqld as a service:
In a DOS window do:
mysqld --debug --standalone
After this you can use the mysql.exe command-line tool in a
second DOS window to reproduce the problem. You can take down the above
mysqld server with mysqladmin shutdown.
Note that the trace file will get very big! If you want to have a smaller trace file, you can use something like:
mysqld --debug=d,info,error,query,general,where:O,/tmp/mysqld.trace
which only prints information with the most interesting tags in `/tmp/mysqld.trace'.
If you make a bug report about this, please only send the lines from the trace file to the appropriate mailing list where something seems to go wrong! If you can't locate the wrong place, you can ftp the trace file, together with a full bug report, to ftp://support.mysql.com/pub/mysql/secret/ so that a MySQL developer can take a look a this.
The trace file is made with the DBUG package by Fred Fish. 「E.3 The DBUG Package」節参照.
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。
We recommend you
to upgrade to gdb 5.1 ASAP as thread debugging works much better with this
version!
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 full gdb> exit
「A.4.1 What To Do If MySQL Keeps Crashing」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 ... backtrace full # mysqld がクラッシュした際、これを行います
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 や /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。
「8.2.2 The DBI Interface」節参照.
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. 「4.9.1 The Error Log」節参照. To get a stack trace,
you must not compile mysqld with the -fomit-frame-pointer
option to gcc. 「E.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 0x40077552 0x81281a0 0x8128f47 0x8127be0 0x8127995 0x8104947 0x80ff28f 0x810131b 0x80ee4bc 0x80c3c91 0x80c6b43 0x80c1fd9 0x80c1686
you can find where mysqld died by doing the following:
mysqld server:
nm -n libexec/mysqld > /tmp/mysqld.symNote 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
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! 「1.6.1.3 バグや問題を報告する方法」節参照.
Note that before starting mysqld with --log you should
check all your tables with myisamchk.
「4 Database Administration」節参照.
もし mysqld が死んだりハングしたりするなら、 mysqld を
--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。
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。
「5.2.1 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. 「4.9.5 The Slow Query Log (3.23.28以上)」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 ( 「4 Database Administration」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
http://www.mysql.com/.
If you have started mysqld 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. 「4.1.1 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.
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：
mysqladmin shutdown).
myisamchk -s database/*.MYI で全テーブルをチェック.
myisamchk -r database/table.MYI で悪いテーブルを修正。
mysqld with --log-bin. 「4.9.4 The Binary Update Log バイナリ更新ログ (3.23.15以上)」節参照.
If you want to find a query that crashes mysqld, you should use
--log --log-bin.
mysqld server を停止。
mysqld server を --log-bin なしで 起動。
mysqlbinlog update-log-file | mysql.
The update log is saved in the MySQL database directory with
the name hostname-bin.#.
mysqld to die with the
above command, you have found reproducible bug that should be easy to
fix! FTP the tables and the binary log to
ftp://support.mysql.com/pub/mysql/secret/ and send a mail to
bugs@lists.mysql.com or (if you are a support customer) to
support@mysql.com about the problem and the MySQL team
will fix it as soon as possible.
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.
To be able to debug a MySQL client with the integrated debug package,
you should configure MySQL with --with-debug or
--with-debug=full. 「2.3.3 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. 「1.6.1.3 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.
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. 「E.1.2 Creating Trace Files」節参照.
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:
<field_1>:<field_2>:...:<field_N>
Each field consists of a mandatory flag character followed by an optional "," and comma-separated list of modifiers:
flag[,modifier,modifier,...,modifier]
The currently recognised flag characters are:
| Flag | Description |
| 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:
-#d:t -#d:f,main,subr1:F:L:t,20 -#d,input,output,files:n -#d:t:i:O,\\mysqld.trace
In MySQL, common tags to print (with the d option) are:
enter,exit,error,warning,info and
loop.
Currently MySQL only supports table locking for
ISAM/MyISAM and HEAP tables,
page-level locking for BDB tables and
row-level locking for InnoDB tables.
「5.3.1 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 analyse the table lock contention
on your system by checking Table_locks_waited and
Table_locks_immediate environment variables.
To decide if you want to use a table type with row-level locking, you will want to look at what the application does and what the select/update pattern of the data is.
Pros for row locking:
Cons:
GROUP
BY on a large part of the data or if one has to often scan the whole table.
Table locks are superior to page level / row level locks in the following cases:
UPDATE table_name SET column=value WHERE unique_key# DELETE FROM table_name WHERE unique_key=#
SELECT combined with INSERT (and very few UPDATEs
and DELETEs).
GROUP BY on the whole table without any writers.
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:
Most web applications do lots of selects, very few deletes, updates mainly on keys, and inserts in some specific tables. The base MySQL setup is very well tuned for this.
Concurrent users are not a problem if one doesn't mix updates with selects that need 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 help.
If you get speed problems with the table locks in MySQL, you
may be able to solve these by converting some of your tables to InnoDB
or BDB tables.
「7.5 InnoDB テーブル (3.23.6以上)」節参照. 「7.6 BDB or BerkeleyDB Tables」節参照.
The optimisation section in the manual covers a lot of different aspects of how to tune applications. 「5.2.12 最適化に関するその他の助言」節参照.
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:
-DHAVE_rts_threads.
thr_alarm.
thr_alarm. If it runs without any ``warning'', ``error'' or aborted
messages, you are on the right track. Here is a successful run on
Solaris:
Main thread: 1 Thread 0 (5) started Thread: 5 Waiting process_alarm Thread 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 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。
少なくとも3つのタイプのスレッドパッケージがあります：
ps が異なったスレッドを示します。
もし一つのスレッドがアボートした場合、プロセス全体がアボートします。
多くのシステムコールはスレッド安全で、オーバーヘッドはとても少ないです。
Solaris, HP-UX, AIX そして OSF1 がカーネルスレッドを持っています。
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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