PATCH: Forcible delaying of UFS (soft)updates
Jon Hamilton
hamilton at pobox.com
Sat Apr 12 10:24:58 PDT 2003
Dave Hart <davehart at davehart.com>, said on Sat Apr 12, 2003 [04:58:13 PM]:
} Marko Zec said:
[...]
} > If the disk would start spinning every now and than,
} > the whole patch would than become pointless...
}
} As I feared.
}
} > [...] the fact that the modified fsync() just returns
} > without doing anything useful doesn't mean the data will be
} > lost - it will simply be delayed until the next coalesced
} > updating occurs.
}
} Unless, of course, your system or power happens to fail.
} Imagine you have a database program keeping track of banking
} transactions. This program uses fsync() to ensure its
} transaction logs are committed to reliable storage before
} indicating the transaction is completed. Suppose the moment
} after I withdraw $500 from an ATM, the operating system or
} hardware fails at the bank.
Right. So in such a situation, the admin for that system would not
enable this optional behavior. There probably aren't too many cases
where mission critical financial transaction systems run on a laptop
on which the desire is maximal battery life, which is the case from
which this whole patch/discussion derives. It's a conscious tradeoff.
--
Jon Hamilton
hamilton at pobox.com
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