Re: [PATCH v1 2/2] merge: Add merge.aggressive config setting

[Ben Peart <peartben@gmail.com>]

On 4/20/2018 1:22 PM, Elijah Newren wrote:
> On Fri, Apr 20, 2018 at 6:36 AM, Ben Peart <Ben.Peart@microsoft.com> wrote:
>> Add the ability to control the aggressive flag passed to read-tree via a config setting.
> 
> This feels like a workaround to the performance problems with index
> updates in merge-recursive.c.  

This change wasn't done to solve performance problems.  We turned it on 
because it reduced the number of unmerged entries (from 40K to 1) in the 
particular merge we were looking at.  The additional 3 scenarios that 
--aggressive resolves made that much difference.

That said, it makes sense to me to do
> this when rename detection is turned off.  In fact, I think you'd
> automatically want to set aggressive to true whenever rename detection
> is turned off (whether by your merge.renames option or the
> -Xno-renames flag).
> > I can't think of any reason this setting would be useful separate from
> turning rename detection off, and it'd actively harm rename detection
> performance improvements I have in the pipeline.  I'd really prefer to
> not add this option, and instead combine the setting of aggressive
> with the other flag.  Do you have an independent reason for wanting
> this?
> 

While combining them would work for our specific use scenario (since we 
turn both on already along with turning off merge.stat), I really 
hesitate to tie these two different flags and code paths together with a 
single config setting.

While I don't want to needlessly complicate your optimizations in this 
area (they are already complex enough!) I believe we need to keep the 
option to turn on --aggressive without turning off rename detection as a 
viable option.  Perhaps if that is the case, your optimizations have 
less impact or don't apply but the user should be able to make that 
choice for their specific situation.

> Thanks,
> Elijah
>