On Thu, 17 Feb 2005, Tom Lane wrote:
> Evgeny Rodichev <er@sai.msu.su> writes:
>>> Any claimed TPS rate exceeding your disk drive's rotation rate is a
>>> red flag.
>
>> Write cache is enabled under Linux by default all the time I make deal
>> with it (since 1993).
>
> You're playing with fire.
Yes. I'm lucky in this play :)
More seriously, we (with Oleg Bartunov) investigated many platforms/OS
for commercial, scientific and other applications during past 10-12
years. I suppose, virtually all excluding modern mainframes.
For reliability Linux + PostreSQL was found the best one (including the
environment with very frequent unexpected power-off, as at some astronomical
observatories at high mountains).
Hence, I'm lucky :)
>
>> fsync() really works fine as I switch off my notebook everyday 2-3 times,
>> and never had any data loss :)
>
> Given that it's a notebook, it's possible that the hardware is smart
> enough not to power down the disk until the disk is done writing
> everything it's cached. Do you care to try some experiments with
> pulling out the battery while Postgres is busy making updates?
Yes, you are exactly right. All modern HDDs (not entry level ones) has
a huge cache (at device, not at controller), and provide the safe hardware
flush of cache *after* power off (thanks capacitors). My HDD has 16MB cache,
and it is the reason for excellent performance.
Regards,
E.R.
_________________________________________________________________________
Evgeny Rodichev Sternberg Astronomical Institute
email: er@sai.msu.su Moscow State University
Phone: 007 (095) 939 2383
Fax: 007 (095) 932 8841 http://www.sai.msu.su/~er