Re: [HACKERS] Clock with Adaptive Replacement

Hi, Thomas!

> 24 апр. 2018 г., в 2:41, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com> написал(а):
>
> On Fri, Feb 12, 2016 at 10:02 AM, Konstantin Knizhnik
> <k(dot)knizhnik(at)postgrespro(dot)ru> wrote:
>> Are there some well known drawbacks of this approach or it will be
>> interesting to adopt this algorithm to PostgreSQL and measure it impact om
>> performance under different workloads?
>
> I'm not currently planning to work in this area and have done no real
> investigation, so please consider the following to be "water cooler
> talk".

I've intention to make some prototypes in this area, but still I hadn't allocated any time chunks sufficient enough to make anything usefull.

I think that replacement of current CS5 will:
1. allow use of big shared buffers
2. make DIRECT_IO realistic possibility
3. improve BgWriter
4. unify different buffering strategies into single buffer manager (there will be no need in placing VACUUM into special buffer ring)
5. finally allow aio and more efficient prefetching like [0]

Here's what we have about size of shared buffer now [1] (taken from [2]). I believe right hill must be big enough to reduce central pit to zero and make function monotonic: OS page cache knows less about data blocks and is expected to be less efficient.

I'm not sure CART is the best possibility, though.
I think that the right way is to implement many prototypes with LRU, ARC, CAR, CART, and 2Q. Then, benchmark them well. Or even make this algorithm pluggable? But currently we have a lot of dependent parts in the system. I do not even know where to start.

Best regards, Andrey Borodin.

[0] http://diku.dk/forskning/Publikationer/tekniske_rapporter/2004/04-03.pdf
[1] https://4.bp.blogspot.com/-_Zz6X-e9_ok/WlaIvpStBmI/AAAAAAAAAA4/E1NwV-_82-oS5KfmyjoOff_IxUXiO96WwCLcBGAs/s1600/20180110-PTI.png
[2] http://blog.dataegret.com/2018/01/postgresql-performance-meltdown.html