[PATCH 4 of 4 NEW-CONCEPT] track-tags: write all tag changes to a file

[Pierre-Yves David]

On 04/06/2017 05:27 PM, Yuya Nishihara wrote:
> On Thu, 6 Apr 2017 01:09:47 +0200, Pierre-Yves David wrote:
>> On 04/05/2017 10:54 PM, Jun Wu wrote:
>>> I don't think "writing things that hook *may* need to filesystem" is a good
>>> approach. It introduces unnecessary overhead if the hook does not need that
>>> information.
>>
>> I do not find the overhead concerning.
>>
>> The thing to keep in mind is that if they are many things to write down,
>> this also means many thing changed during the transaction. So the
>> overhead is likely minimal. In the tags cases, just updating the various
>> tags related cache is going to be much more expensive that writing this
>> to disk.
>
> I agree Pierre-Yves in that I/O overhead wouldn't matter. On the other hand,
> I think the slowness of calling back an hg command doesn't matter, too.

The cost of a round-trip to Mercurial is close to a minimum of 0.1s. And 
every hooks who needs fine transaction data will have to pay it. 
Possibly multiple time. One the other hand writing down a file is a one 
time operation that do not add overhead to each hook.
So I'm still leaning toward the file solution.

> As the journal extension collects similar information for bookmarks, can't
> we integrate the tag tracking with the journal?

Journal is currently an extension, and an experimental one. I would 
prefer not to be scope bloated into solving the two points aboves before 
getting theses features done.

Journal is also tracking name movement, not transaction. We would have 
to teach journal about transaction first (that is probably something 
useful to do, but more scope bloat :-) )

> Maybe a hook will receive
> some pointer to select the corresponding journal entry, and run "hg journal".

(we could use hg journal --pending, to refer to the current transaction, 
that is something to think about while adding transaction awareness to 
journal.)

-- 
Pierre-Yves David