Re: [PATCH 2/3] ieot: default to not writing IEOT section

[Ben Peart <peartben@gmail.com>]

On 11/13/2018 1:18 PM, Jonathan Nieder wrote:
> Hi,
> 
> Ben Peart wrote:
>> On 11/12/2018 7:39 PM, Jonathan Nieder wrote:
> 
>>> As with EOIE, popular versions of Git do not support the new IEOT
>>> extension yet.  When accessing a Git repository written by a more
>>> modern version of Git, they correctly ignore the unrecognized section,
>>> but in the process they loudly warn
>>>
>>> 	ignoring IEOT extension
>>>
>>> resulting in confusion for users.  Introduce the index extension more
>>> gently by not writing it yet in this first version with support for
>>> it.
> [...]
>>> Introduce a '[index] recordOffsetTable' configuration variable to
>>> control whether the new index extension is written.
>>
>> Why introduce a new setting to disable writing the IEOT extension instead of
>> just using the existing index.threads setting?  If index.threads=1 then the
>> IEOT extension isn't written which (I believe) will accomplish the same
>> goal.
> 
> Do you mean defaulting to index.threads=1?  I don't think that would
> be a good default, but if you have a different change in mind then I'd
> be happy to hear it.
> 
> Or do you mean that if the user has explicitly specified index.threads=true,
> then that should imply index.recordOffsetTable=true so users only have
> to set one setting to turn it on?  I can imagine that working well.
> 

Reading the index with multiple threads requires the EOIE and IEOT 
extensions to exist in the index.  If either extension doesn't exist, 
then the code falls back to the single threaded path.  That means you 
can't have both 1) no warning for old versions of git and 2) 
multi-threaded reading for new versions of git.

If you set index.threads=1, that will prevent the IEOT extension from 
being written and there will be no "ignoring IEOT extension" warning in 
older versions of git.

With this patch 'as is' you would have to set both index.threads=true 
and index.recordOffsetTable=true to get multi-threaded index reads.  If 
either is set to false, it will silently drop back to single threaded reads.

> Thanks,
> Jonathan
>