On 16/10/17 13:45, Wido den Hollander wrote:
>> Op 26 september 2017 om 16:39 schreef Mark Nelson <mnelson@xxxxxxxxxx>:
>> On 09/26/2017 01:10 AM, Dietmar Rieder wrote:
>>> thanks David,
>>>
>>> that's confirming what I was assuming. To bad that there is no
>>> estimate/method to calculate the db partition size.
>>
>> It's possible that we might be able to get ranges for certain kinds of
>> scenarios. Maybe if you do lots of small random writes on RBD, you can
>> expect a typical metadata size of X per object. Or maybe if you do lots
>> of large sequential object writes in RGW, it's more like Y. I think
>> it's probably going to be tough to make it accurate for everyone though.
>
> So I did a quick test. I wrote 75.000 objects to a BlueStore device:
>
> root@alpha:~# ceph daemon osd.0 perf dump|jq '.bluestore.bluestore_onodes'
> 75085
> root@alpha:~#
>
> I then saw the RocksDB database was 450MB in size:
>
> root@alpha:~# ceph daemon osd.0 perf dump|jq '.bluefs.db_used_bytes'
> 459276288
> root@alpha:~#
>
> 459276288 / 75085 = 6116
>
> So about 6kb of RocksDB data per object.
>
> Let's say I want to store 1M objects in a single OSD I would need ~6GB of DB space.
>
> Is this a safe assumption? Do you think that 6kb is normal? Low? High?
>
> There aren't many of these numbers out there for BlueStore right now so I'm trying to gather some numbers.
>
> Wido
If I check for the same stats on OSDs in my production cluster I see similar but variable values:
root@vm-ds-01:~/ceph-conf# for i in {0..9} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.0 db per object: 7490
osd.1 db per object: 7523
osd.2 db per object: 7378
osd.3 db per object: 7447
osd.4 db per object: 7233
osd.5 db per object: 7393
osd.6 db per object: 7074
osd.7 db per object: 7967
osd.8 db per object: 7253
osd.9 db per object: 7680
root@vm-ds-02:~# for i in {10..19} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.10 db per object: 5168
osd.11 db per object: 5291
osd.12 db per object: 5476
osd.13 db per object: 4978
osd.14 db per object: 5252
osd.15 db per object: 5461
osd.16 db per object: 5135
osd.17 db per object: 5126
osd.18 db per object: 9336
osd.19 db per object: 4986
root@vm-ds-03:~# for i in {20..29} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.20 db per object: 5115
osd.21 db per object: 4844
osd.22 db per object: 5063
osd.23 db per object: 5486
osd.24 db per object: 5228
osd.25 db per object: 4966
osd.26 db per object: 5047
osd.27 db per object: 5021
osd.28 db per object: 5321
osd.29 db per object: 5150
root@vm-ds-04:~# for i in {30..39} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.30 db per object: 6658
osd.31 db per object: 6445
osd.32 db per object: 6259
osd.33 db per object: 6691
osd.34 db per object: 6513
osd.35 db per object: 6628
osd.36 db per object: 6779
osd.37 db per object: 6819
osd.38 db per object: 6677
osd.39 db per object: 6689
root@vm-ds-05:~# for i in {40..49} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.40 db per object: 5335
osd.41 db per object: 5203
osd.42 db per object: 5552
osd.43 db per object: 5188
osd.44 db per object: 5218
osd.45 db per object: 5157
osd.46 db per object: 4956
osd.47 db per object: 5370
osd.48 db per object: 5117
osd.49 db per object: 5313
I'm not sure why so much variance (these nodes are basically identical) and I think that the db_used_bytes includes the WAL at least in my case, as I don't have a separate WAL device. I'm not sure how big the WAL is relative to metadata and hence how much this might be thrown off, but ~6kb/object seems like a reasonable value to take for back-of-envelope calculating.
[bonus hilarity]
On my all-in-one-SSD OSDs, because bluestore reports them entirely as db space, I get results like:
root@vm-hv-01:~# for i in {60..65} ; do echo -n "osd.$i db per object: " ; expr `ceph daemon osd.$i perf dump | jq '.bluefs.db_used_bytes'` / `ceph daemon osd.$i perf dump | jq '.bluestore.bluestore_onodes'` ; done
osd.60 db per object: 80273
osd.61 db per object: 68859
osd.62 db per object: 45560
osd.63 db per object: 38209
osd.64 db per object: 48258
osd.65 db per object: 50525
Rich
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