Re: [9fans] 9p2k, fsync

["rob pike" <rob@plan9.bell-labs.com>]

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No one here said, ``the file server will take care of it''. What we're
saying is that the file server must take care of it if anyone will.

-rob


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From: Dan Cross <cross@math.psu.edu>
To: 9fans@cse.psu.edu
Cc: 
Subject: Re: [9fans] 9p2k, fsync
Date: Thu, 8 Feb 2001 01:01:27 -0500 (EST)
Message-ID: <200102080601.BAA04455@augusta.math.psu.edu>

In article <200102080115.UAA26741@smtp1.fas.harvard.edu> you write:
>There are no asynchronous writes here.

Define asychronous in this context.  There are no asychronous network
transactions, true, but that's not the same thing as an asychronous
write

>By the time the write(2) system call returns,
>the file server has acknowledged receipt of the data.
>At that point, it's the file server's business.

Not really; if my application depends on that data being on stable
storage, not just a RAM buffer, I could still be in trouble.  The
scenarios are obvious, but the point is that I might have a real need
for this sort of thing, and ``the file server will take care of it''
isn't really good enough.

>Fsync is simultaneously too much and too little.
>People who care often care about making sure
>individual blocks are committed to storage, and fsync
>is the only hammer they have.

When the file is modeled as a stream of bytes, ie, the blocks are
abstracted away from me as the programmer, I'm not sure that hammer
isn't the only one appropriate for the nails I'm given.

>I'm sure that if there were a Tsync message in
>the protocol, it would suffer the same problem.
>Nine times out of ten it would be the wrong hammer.

Yeah, I won't disagree with you there, but that doesn't make it any
less useful.  It's a choice between a hammer for both nails and screws,
or using my hands for both.

	- Dan C.

(Of course, I'd use a skateboard truck instead of my hands, but you get
the idea.  I had to do that once repairing a ramp.  :-)