Questions of KeyValueStore (leveldb) backend

Questions of KeyValueStore (leveldb) backend

[Guang Yang]

Hello Haomai,
We are evaluating the key-value store backend which comes along with Firefly release (thanks for implementing it in Ceph), it is very promising for a couple of our use cases, after going through the related code change, I have a couple of questions which needs your help:
  1. One observation is that, for object larger than 1KB, it will be striped to multiple chunks (k-v in the leveldb table), with one strip as 1KB size. Is there any particular reason we choose 1KB as the strip size (and I didn’t find a configuration to tune this value)?

  2. This is properly a leveldb question, do we expect performance degradation as the leveldb instance keeps increasing (e.g. several TB)?

Thanks,
Guang--
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Re: Questions of KeyValueStore (leveldb) backend

[Haomai Wang]

On Mon, May 26, 2014 at 9:46 AM, Guang Yang <yguang11@outlook.com> wrote:
> Hello Haomai,
> We are evaluating the key-value store backend which comes along with Firefly release (thanks for implementing it in Ceph), it is very promising for a couple of our use cases, after going through the related code change, I have a couple of questions which needs your help:
>   1. One observation is that, for object larger than 1KB, it will be striped to multiple chunks (k-v in the leveldb table), with one strip as 1KB size. Is there any particular reason we choose 1KB as the strip size (and I didn’t find a configuration to tune this value)?

1KB is not a serious value, this value can be configured in the near future.

>
>   2. This is properly a leveldb question, do we expect performance degradation as the leveldb instance keeps increasing (e.g. several TB)?

Ceph OSD is expected to own a physical disk, normally is several
TB(1-4TB). LevelDB can take it easy. Especially we use it to store
large value(compared to normal application usage).

>
> Thanks,
> Guang



-- 
Best Regards,

Wheat
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Re: Questions of KeyValueStore (leveldb) backend

[Guang Yang]

Thanks!
On May 26, 2014, at 12:55 PM, Haomai Wang <haomaiwang@gmail.com> wrote:

> On Mon, May 26, 2014 at 9:46 AM, Guang Yang <yguang11@outlook.com> wrote:
>> Hello Haomai,
>> We are evaluating the key-value store backend which comes along with Firefly release (thanks for implementing it in Ceph), it is very promising for a couple of our use cases, after going through the related code change, I have a couple of questions which needs your help:
>>  1. One observation is that, for object larger than 1KB, it will be striped to multiple chunks (k-v in the leveldb table), with one strip as 1KB size. Is there any particular reason we choose 1KB as the strip size (and I didn’t find a configuration to tune this value)?
> 
> 1KB is not a serious value, this value can be configured in the near future.
> 
>> 
>>  2. This is properly a leveldb question, do we expect performance degradation as the leveldb instance keeps increasing (e.g. several TB)?
> 
> Ceph OSD is expected to own a physical disk, normally is several
> TB(1-4TB). LevelDB can take it easy. Especially we use it to store
> large value(compared to normal application usage).
> 
>> 
>> Thanks,
>> Guang
> 
> 
> 
> -- 
> Best Regards,
> 
> Wheat
> 

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Re: Questions of KeyValueStore (leveldb) backend

[Wido den Hollander]

On 05/26/2014 06:55 AM, Haomai Wang wrote:
> On Mon, May 26, 2014 at 9:46 AM, Guang Yang <yguang11@outlook.com> wrote:
>> Hello Haomai,
>> We are evaluating the key-value store backend which comes along with Firefly release (thanks for implementing it in Ceph), it is very promising for a couple of our use cases, after going through the related code change, I have a couple of questions which needs your help:
>>    1. One observation is that, for object larger than 1KB, it will be striped to multiple chunks (k-v in the leveldb table), with one strip as 1KB size. Is there any particular reason we choose 1KB as the strip size (and I didn’t find a configuration to tune this value)?
>
> 1KB is not a serious value, this value can be configured in the near future.
>

So that is currently hardcoded? I can't find any reference to it in 
config_opts.h

>>
>>    2. This is properly a leveldb question, do we expect performance degradation as the leveldb instance keeps increasing (e.g. several TB)?
>
> Ceph OSD is expected to own a physical disk, normally is several
> TB(1-4TB). LevelDB can take it easy. Especially we use it to store
> large value(compared to normal application usage).
>

With a large value you mean something like 4MB? The regular strip-size 
for RBD, CephFS and such?

>>
>> Thanks,
>> Guang
>
>
>


-- 
Wido den Hollander
42on B.V.

Phone: +31 (0)20 700 9902
Skype: contact42on
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Re: Questions of KeyValueStore (leveldb) backend

[Haomai Wang]

On Mon, May 26, 2014 at 5:23 PM, Wido den Hollander <wido@42on.com> wrote:
> On 05/26/2014 06:55 AM, Haomai Wang wrote:
>>
>> On Mon, May 26, 2014 at 9:46 AM, Guang Yang <yguang11@outlook.com> wrote:
>>>
>>> Hello Haomai,
>>> We are evaluating the key-value store backend which comes along with
>>> Firefly release (thanks for implementing it in Ceph), it is very promising
>>> for a couple of our use cases, after going through the related code change,
>>> I have a couple of questions which needs your help:
>>>    1. One observation is that, for object larger than 1KB, it will be
>>> striped to multiple chunks (k-v in the leveldb table), with one strip as 1KB
>>> size. Is there any particular reason we choose 1KB as the strip size (and I
>>> didn’t find a configuration to tune this value)?
>>
>>
>> 1KB is not a serious value, this value can be configured in the near
>> future.
>>
>
> So that is currently hardcoded? I can't find any reference to it in
> config_opts.h

Yes

>
>
>>>
>>>    2. This is properly a leveldb question, do we expect performance
>>> degradation as the leveldb instance keeps increasing (e.g. several TB)?
>>
>>
>> Ceph OSD is expected to own a physical disk, normally is several
>> TB(1-4TB). LevelDB can take it easy. Especially we use it to store
>> large value(compared to normal application usage).
>>
>
> With a large value you mean something like 4MB? The regular strip-size for
> RBD, CephFS and such?

Not 4MB, it should be 4KB matching the default page size in kernel. Or
4MB for radosgw goal.
I want to match the operation "set_alloc_size" and make it better for workload.


>
>>>
>>> Thanks,
>>> Guang
>>
>>
>>
>>
>
>
> --
> Wido den Hollander
> 42on B.V.
>
> Phone: +31 (0)20 700 9902
> Skype: contact42on



-- 
Best Regards,

Wheat
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