[Bug 1463] New: poor performance with large block size

[Wallace Matthews]

I apologize to Craig. Chris is correct.
I had been reading so many of Chris's highly intelligent e-mails that for some reason my brain
ascribed the comment to Chris. 

But, the comment seems to have been right on. I have re-run the experiment with block sizes as small as 3000 (yes it took a long time to complete) all the way up to block sizes of 100000 with it working in reasonable times. But, when the block size approaches 170,000 or so, the performance degrades exponentially. 

I understand that I am testing at the very fringes of what we should expect rsync to do. File sizes of 25Gig and 55Gig are beyond what was originally envisioned (based on 64k hash buckets and a sliding window of 256k).

I am very impressed that rsync is functional at these file sizes. The developers are doing a great job.

wally

-----Original Message-----
From: Chris Shoemaker [mailto:c.shoemaker at cox.net]
Sent: Wednesday, June 16, 2004 1:45 PM
To: samba-bugs at samba.org
Cc: rsync-qa at samba.org
Subject: Re: [Bug 1463] New: poor performance with large block size


On Wed, Jun 16, 2004 at 06:21:15AM -0700, samba-bugs at samba.org wrote:
> https://bugzilla.samba.org/show_bug.cgi?id=1463
> 
>            Summary: poor performance with large block size
>            Product: rsync
>            Version: 2.6.2
>           Platform: x86
>         OS/Version: other
>             Status: NEW
>           Severity: normal
>           Priority: P3
>          Component: core
>         AssignedTo: wayned at samba.org
>         ReportedBy: wmatthews at sepaton.com
>          QAContact: rsync-qa at samba.org
> 
> 
> I have a 29Gig file that is the previous version of a file and a 1.3 Gig 
> incremental backup of the file. I did the transfer with no block size option 
> and it takes about 6 minutes (GigEthernet). I used --block-size = 90k and it 
> took about 6 minutes. I used --block-size=182000 (close to the square root of 
> 29 Gig) and it only completed ~50 Meg of transfer of the 1.3 Gig in a couple of 
> hours.
> 
> Chris Shoemaker suggests this is a problem with the sliding window being a 
> fixed size of 256k and that the block size will not allow multiple blocks in 
> the window size. 

Er, that suggestion sounds WAY too intelligent to have come from me.  :-)
Seriously, that was Craig Barratt.
-chris

> 
> Operating system is Redhat 9.1 for both systems. Both systems have the 2.6.2 
> with only 1 patch and it is the one Wayne provided for --bwlimit being bi-modal
> 
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