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Unformatted text preview: es. AFS, Coda (in its strongly-connected mode), and
NFS write ﬁle modiﬁcations synchronously to the server
on close. Directory caching in these ﬁle systems is writethrough. Sp eculator would substantially improve write p er19
formance in these ﬁle systems by hiding the latency of these
synchronous op erations. Since ﬁle modiﬁcations may not b e
written back to the server until the ﬁle is closed, data can
b e lost in the event of a system crash. Echo caches modiﬁcations for longer p eriods of time and writes back mod- • If no conﬂicting
writes, longer Tx
• But possibly
harder for app to
• What about nontransactional
18 200 NFS
BlueFS 10 100 From Nightingale, SOSP 2005 5 0 0 No delay 30ms delay This ﬁgure shows the time to run the PostMark benchmark.
Each value is the mean of 5 trials—the error bars are 90%
conﬁdence intervals. Note that the scale of the y-axis diﬀers 20 How?
Modify A Modify B Server Client 1 Client 2 Modify A Write speculate Commit Server • create_speculation Client 2 Write+Commit – Normal client code goes here Modify B
Getattr Write Open C
Open B speculate Commit Getattr Getattr Getattr Open C Open B speculate Open B (a) Unmodiﬁed NFS (b) Sp eculative NFS Figure 1: Example ofNightingale, SOSP 2005 cution for NFS
From speculative exe 21
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- Spring '12