Re: [PATCHSET v2] Add support for write life time hints

[Jens Axboe <axboe@kernel.dk>]

On 06/16/2017 09:52 AM, Christoph Hellwig wrote:
> On Fri, Jun 16, 2017 at 08:40:11AM -0600, Jens Axboe wrote:
>> On 06/16/2017 07:58 AM, Christoph Hellwig wrote:
>>>> >From my perspective, all I really care about is the 4 hints. It's a
>>>> simple enough interface that applications can understand and use it, and
>>>> we don't need any management of actual stream IDs. I think that has the
>>>> highest chance of success. Modifying an application to use it is
>>>> trivial, even something like RocksDB (if you havehad to make changes
>>>> to RocksDB, you'll get this).
>>>
>>> Btw, are your current RocksDB patches available somewhere?
>>
>> Yep, it's on Mark Callaghan's github:
>>
>> https://github.com/mdcallag/rocksdb
>>
>> This is using mostly the v1 I posted, the only difference is that I just
>> named the four flags RWF_S[1-4].
> 
> That commits look a bit like mess, but I guess I shouldn't expect
> kernel-style changelogs and patch separation on github :)

It's just a quick test patch, not intended to be pushed upstream in its
current state. But it's good enough to validate it for testing. In summary,
what the patch does is:

- Redo log, level 0 and 1 of the LSM goes to stream 1.
- Level 2 goes to stream 2
- Level 3 goes to stream 3
- Level 4 and above goes to stream 4.

Each level is roughly 10x in size, but written at the same rate. So each
level roughly has a life time 10x of data writes of the previous one.

-- 
Jens Axboe