[PATCH 1 of 6 V2] obsstore: add a 'cachekey' method

[Pierre-Yves David]

On 06/06/2017 06:01 PM, Martin von Zweigbergk wrote:
> Here are some timings from a hopefully unbiased third party. These are
> best-of-20 times, in seconds. No extensions enabled. I ran
> "debugupdatecaches" before each series of commands to populate the
> caches (I think both obscache and the radixlink cache are hooked into
> that command).

Can you provides timing for the combination of both. The two series are 
not meant to compete but to collaborate. I've a merge available at:

   hg pull -r cf7fd13ead00 
https://www.mercurial-scm.org/repo/users/marmoute/mercurial/

Also, Can you give use some details on the repo caracteristic? I'm 
getting significantly slower runtime for all of these commands in my 
repository.
                          |  At @   | obscache | radixlink |
> id -r @                  |  0.70   |   0.38   |    0.42   |
> log -r @                 |  1.60   |   1.08   |    0.59   |
> export @                 |  0.71   |   0.33   |    0.59   |
> log -G -r 'draft()'      |  1.19   |   1.22   |    0.74   |
> log -G -r 'draft()' \    |  1.26   |   1.27   |    0.97   |
>   -T '{node} {troubles}' |         |          |           |


> We write Mercurial for users, so I've included commands similar to
> what I use somewhat often (plus "hg id" because Pierre-Yves and Jun
> like it).
>
> So radixlink seems to provide a nice speedup across the board. So I
> vote for getting that series in good enough shape to include it and
> then we can come *consider* adding obscache on top after. I know
> Pierre-Yves wanted to get the cachekey and dualsourcecache pieces in
> at least to simplify further work in the evolve extension, but I'm
> very reluctant to add otherwise unused code (more than just a few
> lines) to core for that reason. What do other reviewers think?
>
>
> On Sun, Jun 4, 2017 at 10:05 PM, Jun Wu <quark at fb.com> wrote:
>> Excerpts from Pierre-Yves David's message of 2017-06-04 01:24:59 +0200:
>>> There is likely something wrong with your timing is you get a 10ms speed
>>> up… since the obscache computation is about 1ms. How are you running
>>> your testing? Do you have your code available somewhere?
>>>
>>> (note: you probably have an outdated version on obscache too, I shaved
>>> it a bit in the past week (1.58ms → 0.95ms))
>>
>> Since I have sent the complete version of radixlink series, I'd like to
>> comment on (re-clarify) some key points:
>>
>>   1. obscache puts Facebook at risk of spending about 10 seconds for a
>>      simple command like "hg id", even if the obsstore is tiny.
>>
>>      That could happen when obscache needs to be rebuilt. Like after a fresh
>>      clone, after a real strip (histedit --abort does a real strip).
>>
>>      radixlink does not have such issue - without a prebuilt index, it's
>>      even a bit faster than what we have today.
>>
>>   2. radixlink speeds up all 4 revsets (obsolete, unstable, bumped,
>>      divergent), while obscache only works for obsolete.
>>
>>      I admit it could be 20ms slower for the "obsolete" set. But if I really
>>      want to work in this area, I believe I can catch up by implementing
>>      efficient laziness (that also applies to other 3 sets).
>>
>>   3. Looking at the future where hash-preserving obsstore is a thing,
>>      radixlink is compatible with it out-of-box. obscache has to be reworked
>>      to support it.
>>
>> I think there is little reason that we want the obscache series. I hope
>> someone from the committee could see through and make the right decision.
>>
>>> [...]
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-- 
Pierre-Yves David