28.12.2007 13:39
Проверка использует ли Oracle асинхронный ввод вывод под Linux

Subject: HOW TO CHECK IF ASYNCHRONOUS I/O IS WORKING ON LINUX Doc ID: Note:237299.1Type: HOWTO Last Revision Date: 19-AUG-2007Status: PUBLISHED
PURPOSE-------In this document we are going to explain how to check that asynchronous I/O (AIO) is working. AIO can be enabled in Oracle 9i 9.2 and higher. SCOPE & APPLICATION-------------------Many times there is a requirement to check if Asynchronous I/O is workingon Linux Platform, so we can try to use it for our datafiles access inside database.SOLUTION--------slabinfo maintains statistics about objects in memory. Some of the structs usedby Asynchronous I/O are threated as objects in the virtual memory, so we can look for those structs on slabinfo. The ones related to AIO are named kio*.$ cat /proc/slabinfo | grep kiofor example:output with async io enabled.$ cat /proc/slabinfo | grep kiokioctx 270 270 128 9 9 1 : 252 126kiocb 66080 66080 96 1652 1652 1 : 252 126kiobuf 236 236 64 4 4 1 : 252 126$ output with async io disabled.$ cat /proc/slabinfo | grep kiokioctx 0 0 128 0 0 1 : 252 126kiocb 0 0 96 0 0 1 : 252 126kiobuf 0 0 64 0 0 1 : 252 126$There are 3 caches involved.The kioctx and kiocb are Async I/O data structures that are defined in aio.h. If it shows a non zero value that means async io is enabled.If you have the source code loaded, you can review it at file aio.h.This file is located under:/usr/src/linux-<version>/include/linux/aio.hThese data structures are using to track the I/O requests, and are allocated as part of the __init_aio_setup() call in aio.c.Example strace of dbw0 process with AIO enabled (init.ora parameterfilesystemio_options = asynch) shows: io_submit(3071864832, 1, {{0xb7302e34, 0, 1, 0, 21}}) = 1 gettimeofday({1176916625, 58882}, NULL) = 0 io_getevents(-1223102464, 1, 1024, {{0xb7302e34, 0xb7302e34, 8192, 0}}, {600, 0}) = 1Example strace of dbw0 process with AIO disabled(filesystemio_options = none): pwrite64(21, "\6\242\0\0004\21\300\0\220B\243\0\0\0\1\6\207\357\0\0\1"..., 8192, 36077568) = 8192 times(NULL) = 1775653082 times(NULL) = 1775653082 pwrite64(21, "\6\242\0\0<\21\300\0\220B\243\0\0\0\1\6\254\0\0\0\2\0*"..., 8192, 36143104) = 8192CAVEAT FOR ASMLib -----------------If Oracle ASMLib (see ) is deployed, the kiocb structs are not used. ASMLib does not use the POSIX aio_*() functions. You will never see any kioctx or kiocb structures from ASMLib. It is far lower level than that.In fact, ASMLib does AIO or SyncIO depending on how the I/O is passed to it,It makes no decisions at all. This is entirely up to kfk and the layers above it,kfk is entirely controlled by the disk_asynch_io parameter.So, we can check whether ASMLib is doing AIO by PL/SQL command "show param disk_asynch_io".(You can disable AIO by set disk_asynch_io=false)With ASMLib, AIO is done via ioctl() calls (2.4 kernel), or read() calls (2.6 kernel) on the ASM device. Whether ASMLib uses aio depends on whether oracle is configured to do aio,In oracle 10g, if ASMLib is in use, the i/o is asynchronous,because oracle 10g enables aio by default.The strace when using ASMlib will show read calls that look like this: read(16, "MSA\0\2\0\10\0P\0\0\0\222\377\377\377@\313\373\5\0\0\0"..., 80) = 80The first 3 characters, byte-swapped, are ASM, indicating an ASMLib I/Ocommand structure.
Тип файла: zip asyncIOlinux.zip (2.5 Кб, 156 просмотров)
29.12.2007 10:09
К примеру у меня на SLES-9-x86_64-SP3
с filesystemio_options = setall (directio) база вообще не запускается,
а filesystemio_options = asynch мне показалось, что база намного дольше выключается после продолжительного время работы. В производительности разницы не заметил.

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