Re: pool distribution quality report script

[Mark Nelson <mnelson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

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Hi Blair,

I've updated the script and it now (theoretically) computes optimal 
crush weights based on both primary and secondary acting set OSDs.  It 
also attempts to show you the efficiency of equal weights vs using 
weights optimized for different pools (or all pools).  This is done by 
looking at the way weights would be assigned and how they would affect 
the current pool distribution, then looking at the skew for the heaviest 
weighted OSD vs the average.

Unfortunately the output has now become beastly and complex (granted 
this is a large cluster with many pools!).  I think the trick now is how 
to make the interface for this more manageable.  For instance perhaps 
it's not interesting to know how one pool's weights affect the 
efficiency of the acting primary OSDs for another pool.

I've included sample output, but it's huge (15K lines long!)

Mark

On 03/05/2015 01:52 AM, Blair Bethwaite wrote:
> Hi Mark,
>
> Cool, that looks handy. Though it'd be even better if it could go a
> step further and recommend re-weighting values to balance things out
> (or increased PG counts where needed).
>
> Cheers,
>
> On 5 March 2015 at 15:11, Mark Nelson <mnelson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
>> Hi All,
>>
>> Recently some folks showed interest in gathering pool distribution
>> statistics and I remembered I wrote a script to do that a while back. It was
>> broken due to a change in the ceph pg dump output format that was committed
>> a while back, so I cleaned the script up, added detection of header fields,
>> automatic json support, and also added in calculation of expected max and
>> min PGs per OSD and std deviation.
>>
>> The script is available here:
>>
>> https://github.com/ceph/ceph-tools/blob/master/cbt/tools/readpgdump.py
>>
>> Some general comments:
>>
>> 1) Expected numbers are derived by treating PGs and OSDs as a
>> balls-in-buckets problem ala Raab & Steger:
>>
>> http://www14.in.tum.de/personen/raab/publ/balls.pdf
>>
>> 2) You can invoke it either by passing it a file or stdout, ie:
>>
>> ceph pg dump -f json | ./readpgdump.py
>>
>> or
>>
>> ./readpgdump.py ~/pgdump.out
>>
>>
>> 3) Here's a snippet of some of some sample output from a 210 OSD cluster.
>> Does this output make sense to people?  Is it useful?
>>
>>> [nhm@burnupiX tools]$ ./readpgdump.py ~/pgdump.out
>>>
>>> +----------------------------------------------------------------------------+
>>> | Detected input as plain
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>>
>>>
>>> +----------------------------------------------------------------------------+
>>> | Pool ID: 681
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | Participating OSDs: 210
>>> |
>>> | Participating PGs: 4096
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Primary Role (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 4, Max: 33, Mean: 19.5, Std Dev: 7.2
>>> |
>>> | Actual PGs Per OSD: Min: 7, Max: 43, Mean: 19.5, Std Dev: 6.5
>>> |
>>> | 5 Most Subscribed OSDs: 199(43), 175(36), 149(34), 167(32), 20(31)
>>> |
>>> | 5 Least Subscribed OSDs: 121(7), 46(7), 70(8), 94(9), 122(9)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 54.6%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Secondary Role (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 18, Max: 59, Mean: 39.0, Std Dev: 10.2
>>> |
>>> | Actual PGs Per OSD: Min: 17, Max: 61, Mean: 39.0, Std Dev: 9.7
>>> |
>>> | 5 Most Subscribed OSDs: 44(61), 14(60), 2(59), 167(59), 164(57)
>>> |
>>> | 5 Least Subscribed OSDs: 35(17), 31(20), 37(20), 145(20), 16(20)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 36.0%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in All Roles (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 32, Max: 83, Mean: 58.5, Std Dev: 12.5
>>> |
>>> | Actual PGs Per OSD: Min: 29, Max: 93, Mean: 58.5, Std Dev: 14.6
>>> |
>>> | 5 Most Subscribed OSDs: 199(93), 175(92), 44(92), 167(91), 14(91)
>>> |
>>> | 5 Least Subscribed OSDs: 121(29), 35(30), 47(30), 131(32), 145(32)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 37.1%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Primary Role (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 4, Max: 33, Mean: 19.5, Std Dev: 7.2
>>> |
>>> | Actual PGs Per OSD: Min: 7, Max: 43, Mean: 19.5, Std Dev: 6.5
>>> |
>>> | 5 Most Subscribed OSDs: 199(43), 175(36), 149(34), 167(32), 20(31)
>>> |
>>> | 5 Least Subscribed OSDs: 121(7), 46(7), 70(8), 94(9), 122(9)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 54.6%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Secondary Role (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 18, Max: 59, Mean: 39.0, Std Dev: 10.2
>>> |
>>> | Actual PGs Per OSD: Min: 17, Max: 61, Mean: 39.0, Std Dev: 9.7
>>> |
>>> | 5 Most Subscribed OSDs: 44(61), 14(60), 2(59), 167(59), 164(57)
>>> |
>>> | 5 Least Subscribed OSDs: 35(17), 31(20), 37(20), 145(20), 16(20)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 36.0%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in All Roles (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 32, Max: 83, Mean: 58.5, Std Dev: 12.5
>>> |
>>> | Actual PGs Per OSD: Min: 29, Max: 93, Mean: 58.5, Std Dev: 14.6
>>> |
>>> | 5 Most Subscribed OSDs: 199(93), 175(92), 44(92), 167(91), 14(91)
>>> |
>>> | 5 Least Subscribed OSDs: 121(29), 35(30), 47(30), 131(32), 145(32)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 37.1%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>
>>
>> This is shown for all the pools, followed by the totals:
>>
>>>
>>> +----------------------------------------------------------------------------+
>>> | Pool ID: Totals (All Pools)
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | Participating OSDs: 210
>>> |
>>> | Participating PGs: 131072
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Primary Role (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 542, Max: 705, Mean: 624.0, Std Dev: 40.8
>>> |
>>> | Actual PGs Per OSD: Min: 356, Max: 917, Mean: 624.0, Std Dev: 176.2
>>> |
>>> | 5 Most Subscribed OSDs: 167(917), 123(876), 23(873), 194(869), 60(868)
>>> |
>>> | 5 Least Subscribed OSDs: 117(356), 155(358), 46(361), 78(361), 70(362)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 32.0%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Secondary Role (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 1132, Max: 1363, Mean: 1248.0, Std Dev: 57.8
>>> |
>>> | Actual PGs Per OSD: Min: 864, Max: 1554, Mean: 1248.0, Std Dev: 229.9
>>> |
>>> | 5 Most Subscribed OSDs: 182(1554), 142(1552), 4(1548), 123(1544),
>>> 100(1540)|
>>> | 5 Least Subscribed OSDs: 16(864), 55(885), 18(885), 42(885), 85(891)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 19.7%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in All Roles (Acting)
>>> |
>>> | Expected PGs Per OSD: Min: 1730, Max: 2013, Mean: 1872.0, Std Dev: 70.7
>>> |
>>> | Actual PGs Per OSD: Min: 1252, Max: 2420, Mean: 1872.0, Std Dev: 402.0
>>> |
>>> | 5 Most Subscribed OSDs: 123(2420), 142(2403), 195(2390), 100(2389),
>>> 182(2380)|
>>> | 5 Least Subscribed OSDs: 55(1252), 42(1268), 16(1271), 85(1271),
>>> 155(1275) |
>>> | Avg Deviation from Most Subscribed OSD: 22.6%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Primary Role (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 542, Max: 705, Mean: 624.0, Std Dev: 40.8
>>> |
>>> | Actual PGs Per OSD: Min: 356, Max: 917, Mean: 624.0, Std Dev: 176.2
>>> |
>>> | 5 Most Subscribed OSDs: 167(917), 123(876), 23(873), 194(869), 60(868)
>>> |
>>> | 5 Least Subscribed OSDs: 117(356), 155(358), 46(361), 78(361), 70(362)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 32.0%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in Secondary Role (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 1132, Max: 1363, Mean: 1248.0, Std Dev: 57.8
>>> |
>>> | Actual PGs Per OSD: Min: 864, Max: 1554, Mean: 1248.0, Std Dev: 229.9
>>> |
>>> | 5 Most Subscribed OSDs: 182(1554), 142(1552), 4(1548), 123(1544),
>>> 100(1540)|
>>> | 5 Least Subscribed OSDs: 16(864), 55(885), 18(885), 42(885), 85(891)
>>> |
>>> | Avg Deviation from Most Subscribed OSD: 19.7%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>> | OSDs in All Roles (Up)
>>> |
>>> | Expected PGs Per OSD: Min: 1730, Max: 2013, Mean: 1872.0, Std Dev: 70.7
>>> |
>>> | Actual PGs Per OSD: Min: 1252, Max: 2420, Mean: 1872.0, Std Dev: 402.0
>>> |
>>> | 5 Most Subscribed OSDs: 123(2420), 142(2403), 195(2390), 100(2389),
>>> 182(2380)|
>>> | 5 Least Subscribed OSDs: 55(1252), 42(1268), 16(1271), 85(1271),
>>> 155(1275) |
>>> | Avg Deviation from Most Subscribed OSD: 22.6%
>>> |
>>>
>>> +----------------------------------------------------------------------------+
>>
>>
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