Re: LevelDB support status is still experimental on Giant?

["Chen, Xiaoxi" <xiaoxi.chen@xxxxxxxxx>]

Range query is not that important in nowadays SSD----you can see very high read random read IOPS in ssd spec, and getting higher day by day.The key problem here is trying to exactly matching one query(get/put) to one SSD IO(read/write), eliminate the read/write amplification. We kind of believe OpenNvmKV may be the right approach.

 

Back to the context of Ceph,  can we find some use case of nowadays key-value backend?  We would like to learn from community what’s the workload pattern if you wants a K-V backed Ceph? Or just have a try?  I think before we get a suitable DB backend ,we had better off to optimize the key-value backend code to support specified kind of load.

 

 

 

From: Haomai Wang [mailto:haomaiwang@xxxxxxxxx]
Sent: Monday, December 1, 2014 10:14 PM
To: Chen, Xiaoxi
Cc: Satoru Funai; ceph-users@xxxxxxxx
Subject: Re: [ceph-users] LevelDB support status is still experimental on Giant?

 

Exactly, I'm just looking forward a better DB backend suitable for KeyValueStore. It maybe traditional B-tree design.

 

Kinetic original I think it was a good backend, but it doesn't support range query :-(

 

 

 

On Mon, Dec 1, 2014 at 10:04 PM, Chen, Xiaoxi <xiaoxi.chen@xxxxxxxxx> wrote:

We have tested it for a while, basically it seems kind of stable but show terrible bad performance.

 

This is not the fault of Ceph , but levelDB, or more generally,  all K-V storage with LSM design(RocksDB,etc), the LSM tree structure naturally introduce very large write amplification---- 10X to 20X when you have tens GB of data per OSD. So you can always see very bad sequential write performance (~200MB/s for a 12SSD setup), we can share more details on the performance meeting.

 

To this end,  key-value backend with LevelDB is not useable for RBD usage, but maybe workable(not tested) in the LOSF cases ( tons of small objects stored via rados , k-v backend can prevent the FS metadata become the bottleneck)

 

From: ceph-users [mailto:ceph-users-bounces@xxxxxxxxxxxxxx] On Behalf Of Haomai Wang
Sent: Monday, December 1, 2014 9:48 PM
To: Satoru Funai
Cc: ceph-users@xxxxxxxx
Subject: Re: [ceph-users] LevelDB support status is still experimental on Giant?

 

Yeah, mainly used by test env. 

 

On Mon, Dec 1, 2014 at 6:29 PM, Satoru Funai <satoru.funai@xxxxxxxxx> wrote:

Hi guys,
I'm interested in to use key/value store as a backend of Ceph OSD.
When firefly release, LevelDB support is mentioned as experimental,
is it same status on Giant release?
Regards,

Satoru Funai
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Best Regards,

Wheat

 

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Best Regards,

Wheat

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