Re: x206-x225
От | PFC |
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Тема | Re: x206-x225 |
Дата | |
Msg-id | op.s58yeob1cigqcu@apollo13 обсуждение исходный текст |
Ответ на | Re: x206-x225 (Joost Kraaijeveld <J.Kraaijeveld@Askesis.nl>) |
Ответы |
Re: x206-x225
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Список | pgsql-performance |
>> each transaction requires a sync to the disk, a sync requires a real >> write (which you then wait for), so you can only do one transaction per >> rotation. > Not according to a conversation I had with Western Digital about the It depends if you consider that "written to the disk" means "data is somewhere between the OS cache and the platter" or "data is writter on the platter and will survive a power loss". Postgres wants the second option, of course. For that, the data has to be on the disk. Thus, the disk has to seek, wait till the desired sector arrives in front of the head, write, and tell the OS it's done. Your disk just stores data in its embedded RAM buffer and tells the OS it's written, but if you lose power, you lose anything that's in the disk embedded RAM cache... Advanced RAID cards have battery backed up RAM cache precisely for that purpose. Your harddisk doesn't.
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