Re: UndoDB's performance

[Greg Law <glaw@undo-software.com>]

Sean Chen wrote:
> On Tue, Dec 15, 2009 at 11:56 AM, Hui Zhu <teawater@gmail.com> wrote:
>> I did some test but its speed close to prec.  Some others was better.
>> Maybe it have some special performance technology for some code.
>>
>> Hui
>>
>> On Tue, Dec 15, 2009 at 10:40, Sean Chen <sean.chen1234@gmail.com> wrote:
>>> On Mon, Dec 14, 2009 at 11:07 PM, Hui Zhu <teawater@gmail.com> wrote:
>>>> Try undodb.
>>>>
>>>> On Mon, Dec 14, 2009 at 21:18, Sean Chen <sean.chen1234@gmail.com> wrote:
>>>>> On Mon, Dec 14, 2009 at 7:14 PM, Hui Zhu <teawater@gmail.com> wrote:
>>>>>> gdb-7 reverse debugging accelerator.
>>>>>> Regular gdb-7 reverse runs apps          40,000x                slower
>>>>>> UndoDB+gdb-7 reverse runs apps           1.7x            slower!
>>>>>>
>>>>>>
>>>>>> Are you really do some try?
>>>>>> I suggest you do some test on it.  :)
>>>>>>
>>>>>> Thanks,
>>>>>> Hui
>>>>>>
>>>>>> On Fri, Dec 4, 2009 at 23:34, Sean Chen <sean.chen1234@gmail.com> wrote:
>>>>>>> On UndoDbÂ’s website, I saw the following ad.
>>>>>>>
>>>>>>> Regular gdb-7 reverse runs apps 40,000x slower
>>>>>>> UndoDB+gdb-7 reverse runs apps 1.7x slower!
>>>>>>>
>>>>>>> In my experiment, gdb-7 reverse does run apps more than 20,000x
>>>>>>> slower. How does UndoDB improve the performance so much without a
>>>>>>> simulator and without record? Below is its self-introduction on the
>>>>>>> website. UndoDB's "snapshot-and-replay" technique stores periodic
>>>>>>> copy-on-write snapshots of the application and only non-deterministic
>>>>>>> inputs (system calls, thread-switches, shared memory reads, etc).
>>>>>>>
>>>>>>> Are there any obvious disadvantages in UndoDB? I tried to search
>>>>>>> UndoDB in the archive of the mailing list, however, little discussion
>>>>>>> is found.
>>>>>>>
>>>>>>> --
>>>>>>> Best Regards,
>>>>>>> Sean Chen
>>>>>>>
>>>>> ThatÂ’s UndoDBÂ’s ad on its website.
>>>>>
>>>>> In my experiment, gdb-7 reverse runs apps about 22,000x slower.
>>>>>
>>>>> --
>>>>> Best Regards,
>>>>> Sean Chen
>>>>>
>>> I also tried UndoDB, and it is really fast. So I am sure they are
>>> using different strategy.
>>>
>>> --
>>> Best Regards,
>>> Sean Chen
>>>
> 
> It might not use process record technique like your design.
> 
> Below is its self-introduction on its website.
> UndoDB's "snapshot-and-replay" technique stores periodic copy-on-write
> snapshots of the application and only non-deterministic inputs (system
> calls, thread-switches, shared memory reads, etc).
> 
> Any comments?

Yes, I can confirm that's what we do.  We did it that way (and generally 
tried very hard) to get the best record-time performance.  To answer the 
OP, the downside is replay mode performance, namely stepping backwards, 
will be worse because you have a lot more work to do.  You also need to 
store the snapshots, although as noted, copy-on-write can mitigate this 
cost.

Greg
-- 
Greg Law, Undo Software                       http://undo-software.com/