Re: Re: [HACKERS] Wal sync odirect
От | Cédric Villemain |
---|---|
Тема | Re: Re: [HACKERS] Wal sync odirect |
Дата | |
Msg-id | 201307221640.35989.cedric@2ndquadrant.com обсуждение исходный текст |
Ответ на | Re: Re: [HACKERS] Wal sync odirect (Craig Ringer <craig@2ndquadrant.com>) |
Список | pgsql-hackers |
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Lelundi 22 juillet 2013 09:39:50, Craig Ringer a écrit :<p style=" margin-top:0px; margin-bottom:0px;margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> On 07/22/201303:30 PM, Миша Тюрин wrote:<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">> > <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> > i tell about wal_levelis higher than MINIMAL<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> OK, so you want to be ableto force O_DIRECT for wal_level = archive ?<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px;-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> <p style=" margin-top:0px; margin-bottom:0px;margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> I guessthat makes sense if you expect the archive_command to read the<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> file out of the RAID controller'swrite cache before it gets flushed and<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px;-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> your archive_command can also use direct I/Oto avoid pulling it into cache.<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> You already know where tochange to start experimenting with this. What<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px;-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">> exactly are you trying to ask? I don't seeany risk in forcing O_DIRECT<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">> for higher wal_level, but I'm not an expert in WAL and recovery.I'd<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;-qt-user-state:0;">> recommend testing on a non-critical PostgreSQL instance.<p style="-qt-paragraph-type:empty;margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; "> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">IIRC there is also some fadvise() call to flush the buffer cache whenusing <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;-qt-user-state:0;">'minimal', but not when using archiving of WAL.<p style=" margin-top:0px; margin-bottom:0px;margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">I'm unsure howthis has been tunned with streaming replication addition.<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px;margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; "> <p style=" margin-top:0px; margin-bottom:0px;margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">see xlog.c|h<pstyle="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; "> <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0;text-indent:0px; -qt-user-state:0;">-- <p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;margin-right:0px; -qt-block-indent:0; text-indent:0px; -qt-user-state:0;">Cédric Villemain +33 (0)6 20 3022 52<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;-qt-user-state:0;">http://2ndQuadrant.fr/<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px;-qt-block-indent:0; text-indent:0px; -qt-user-state:0;">PostgreSQL: Support 24x7 - Développement, Expertiseet Formation<p style="-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px;-qt-block-indent:0; text-indent:0px; ">
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