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Re: Fresh checkout vs 'svn upgrade': How good is good enough?

From: Stefan Fuhrmann <eqfox_at_web.de>
Date: Sat, 18 Jun 2011 15:34:22 +0200

On 18.06.2011 15:30, Bert Huijben wrote:
> This assumes creating many tempfiles is cheaper then updating/reading
> the db. On Windows that is certainly not the case.
No. We already create these tempfiles today.

-- Stefan^2.
> Bert Huijben (Cell phone) From: Stefan Fuhrmann
> Sent: zaterdag 18 juni 2011 11:19
> To: Philip Martin
> Cc: Johan Corveleyn; Paul Burba; Subversion Development
> Subject: Re: Fresh checkout vs 'svn upgrade': How good is good enough?
> On 16.06.2011 12:50, Philip Martin wrote:
>> Philip Martin<philip.martin_at_wandisco.com> writes:
>>> That's using the sync option on the NFS server. Using async
>>> Checkout using 1.6:
>>> Elapsed: 73s CPU: 16s
>> [...]
>>> Checkout using 1.7
>>> Elapsed: 180s CPU: 26s
>> By comparison the same checkout to a local disk takes about 5s elapsed
>> for both 1.6 and 1.7.
>> I tried an experiment with the update editor used by checkout. At
>> present it inserts a not-present NODES row for each file in add_file()
>> and then replaces it with a normal NODES row in close_file(). I removed
>> the code that inserts the not-present row, the checkout still works
>> provided it runs to completeion. This change removes one transaction
>> per-file from the checkout, and reduces the elapsed time by 27s or 15%.
> This matches exactly what I discovered 3 weeks ago
> but hadn't found the time, yet to investigate in detail.
> So, take the following with a grain of salt.
> My hypothesis is that we need only a single db transaction
> (plus maybe one for managing the pristine store). Without
> changing the editor logic, a file c/o into an empty directory
> should look like this:
> (1) Receive content and stream to pristine temp
> (2) Move to pristine store
> (3) Copy& translate to w/c temp
> (4) Set flags and time stamp
> (5) Add row to NODES
> (6) Move from w/c temp to w/c final location
> (preserving flags and time stamp)
> The above should be valid workflow that can be interrupted
> at any point without corrupting the w/c:
> (before 2 is finished) w/c is locked, temps to be cleared upon cleanup
> (after 2 is finished) orphaned pristine entry, no idea whether we are
> strict about that today; becomes (most likely) used after w/c update
> (before 5 is finished) w/c is locked, temps to be cleared upon cleanup
> (after 5 is finished) w/c looks like the file had been added but got
> deleted manually; update should simply "restore" it
> (6) supposed to be atomic and non-modifying
> In the editor, one of the transactions is commented with
> "mark the parent as incomplete". That mark seems to be
> unnecessary: In case of an interruption, the w/c will need
> to be cleaned up as described above. After that, it looks
> like either the file had not been sent at all or the user
> removed it manually. There is no intermediate state that
> needs to be tracked here.
>> So to get better performance on network disks we have to remove or
>> combine transactions.
> Eliminating transactions should speed up c/o for any
> type of "disk".
> -- Stefan^2.
Received on 2011-06-18 15:34:56 CEST

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