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Re: Lock-free databases

From: Joe Seigh <>
Date: Wed, 09 Nov 2005 11:22:41 -0500
Message-ID: <>

vc wrote:
> Joe Seigh wrote:

>>VC wrote:
>>Lock-free techniques similar to the ones covered by their patents have
>>be used in operating system kernels for decades and those operating systems
>>weren't going around proclaiming they were lock-free.

> Since they "haven't provided any facts significant to anyone familiar
> with lock-free programming techniques", how can you claim that "
> Lock-free techniques similar to the ones covered by their patents have
> be used in operating system kernels for decades and those operating
> systems weren't going around proclaiming they were lock-free".

Because I used to be a mainframe kernel developer and implemented some of those lock-free algorithms. In fact I did an RCU implementation in the mid 80's.


>>In fact use of lock-free
>>techniques like RCU for significant performance benefits doesn't qualify
>>Linux as lock-free since it still has plenty of locks left over.

> So what ? Linux may have plenty of locks left over, but ANTS may not.
> You just do not know if ANTS has any locks, or if it has any left,
> whether the leftover is significant to make their claim false.

I never said their claims are false. I just expressed doubt since I have experience with lock-free algorithms. The burden of proof is on them as far as I'm concerned. If you want to believe their claims that's ok with me.


>>>>their bottlenecks are IPC related, I don't see how their lock-free
>>>>patented techniques would help performance.
>>>There is some evidence (
>>> ) that
>>>operations on lock-free data structures outperform similar lock-based
>>>implementations (without dragging IPC into the picture).
>>Under certain conditions.  It helps if you have contention.  In non-contention
>>cases, regular locks are as fast or faster than lock-free based solutions.

> It may be true for RCU, but not true for other approaches to
> implementing lock-free data structures (you can easily find plenty of
> research results by googling for "performance" and "lock-free").
> Clearly, in some cases lock-based synchronization will outperform
> lock-free algorithms, no one claims otherwise.
>>Having stuff lock-free doesn't automatically make things run faster.

> Of course not. In fact, performance improvements with operations on
> lock-free structures is a recently new phenomenon. Implementating
> lock-free structures requires much more effort than the traditional
> locking approach. But the point is that, judging by many independent
> results, it's possible to achieve performance gain by using such
> structures. Taking into account those results, the ANTS claims that
> lock-free data structures improve performace have more credibility that
> your wholesale denial of their claims.

Well in that article cited earlier they claim to use a lot of techniques to get their performance, not just lock-free. They use in-memory, thread pooling, etc... That's a lot of variables and they haven't quantified how much benefit is gotten from each technique. They just compared their database against a conventional database, not another vendor's in-memory database. That's apples and oranges as far as I'm concerned and doesn't reallly tell me anything about how effective their lock-free techniques are. So when I ask how much benefit can be gotten from using lock-free techniques, saying ANTs claims to be lock-free doesn't provide me with any useful information.

When I test lock-free techniques, I test them against known lock based solutions and against other lock-free techniques. This isn't always done. It's easy to pick a worst case technique to compare your technique against and make it look good.

Joe Seigh

When you get lemons, you make lemonade.
When you get hardware, you make software. 
Received on Wed Nov 09 2005 - 10:22:41 CST

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