[RFC] Ways to make initial knit creation faster (both push and commit)

[John Arbash Meinel]

Robey Pointer wrote:

...

> Something about this didn't seem "right" to me so I dug into it, in
> paramiko.  I'm now pretty convinced that the stat() is unnecessary.
> 
> The later sftp RFC drafts make it clear that the offset in a write is
> ignored when a file is opened for append.  (That makes sense because it
> follows posix: writes to an append-mode file go to the end, no matter
> where the seek pointer is.)

So now we need to decide if it is better to have 'non_atomic_put_bytes'
as a function call. Because it is similar to 'append()', and append has
better "don't destroy existing data" semantics.

I could go either way. Some of my changes just delay when we create the
file, which would help for append just as easily as non_atomic_put_bytes.

I'm tempted to leave non_atomic_put* in, for the case when people don't
have the latest paramiko. But since it was mostly a workaround for
paramiko, it may be better to leave it out.

> 
> The earlier drafts -- the ones that describe the sftp protocol version
> in common use -- are shorter and don't say anything about it, but after
> looking at the sftp code in openssh, they're relying on the same posix
> behavior.  So I think it's safe to assume that if both openssh *and* the
> RFC agree, that's the right thing to do.  (The reason I'm hedging so
> much here is that the RFC tends, in some places, to drift way out beyond
> what any actual implementation does.)
> 
> I've changed paramiko's trunk to avoid the stat() on files opened in
> append mode, postponing it until/if we need it (for example, seek() on
> an O_APPEND|O_RDWR file).  If you think it might still help, I'd
> appreciate any feedback.
> 
> robey
> 

Have you run the 'bzr' test suite with this version of paramiko? I don't
see anything in bzrlib/tests/stub_sftp.py that explicitly handles append
mode. Most likely the 'flags' parameter has the O_APPEND set, but I'm
not sure how that interacts with os.fdopen('rb+')

John
=:->

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