PATCH: Forcible delaying of UFS (soft)updates

[Jon Hamilton]

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