Re: fsync and hardware write cache
pgsql@mohawksoft.com writes:
Something to think about:
if you run PostgreSQL with fsync on, but you use the hardware write cache
on your disk drives, how likely are you to lose data? Obviously, this is a
fairly limited problem, as it only applies to power down (which you can
control) or power loss where the risks may be reduced but not eliminated
with a UPS.Does it make sense to add a platform specific call that will flush a write
cache when fsync is enable?
AIUI, recent versions of the Linux kernel are supposed to do this for
you, but not all drives honor the "flush" command, so you're still at
the mercy of your disk vendor...
-Doug
--
Let us cross over the river, and rest under the shade of the trees.
--T. J. Jackson, 1863
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pgsql@mohawksoft.com wrote:
Something to think about:
if you run PostgreSQL with fsync on, but you use the hardware write cache
on your disk drives, how likely are you to lose data? Obviously, this is a
fairly limited problem, as it only applies to power down (which you can
control) or power loss where the risks may be reduced but not eliminated
with a UPS.Does it make sense to add a platform specific call that will flush a write
cache when fsync is enable?
We have discussed this in the past and just require hardware to honor
the operating system fsync. If it doesn't honor that, how do we fix it
other than telling them to properly configure their hardware.
--
Bruce Momjian | http://candle.pha.pa.us
pgman@candle.pha.pa.us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073Import Notes
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