Re: [HACKERS] autovacuum can't keep up, bloat just continues to rise

On 21/07/17 15:58, Joshua D. Drake wrote:

> On 07/19/2017 07:57 PM, Tom Lane wrote:
>> Peter Geoghegan <pg@bowt.ie> writes:
>>> My argument for the importance of index bloat to the more general
>>> bloat problem is simple: any bloat that accumulates, that cannot be
>>> cleaned up, will probably accumulate until it impacts performance
>>> quite noticeably.
>>
>> But that just begs the question: *does* it accumulate indefinitely, or
>> does it eventually reach a more-or-less steady state?  The traditional
>> wisdom about btrees, for instance, is that no matter how full you pack
>> them to start with, the steady state is going to involve something like
>> 1/3rd free space.  You can call that bloat if you want, but it's not
>> likely that you'll be able to reduce the number significantly without
>> paying exorbitant costs.
>>
>> I'm not claiming that we don't have any problems, but I do think it's
>> important to draw a distinction between bloat and normal operating
>> overhead.
>
> Agreed but we aren't talking about 30% I don't think. Here is where I 
> am at. It took until 30 minutes ago for the tests to finish:
>
>                 name                 |  setting
> -------------------------------------+-----------
>  autovacuum                          | on
>  autovacuum_analyze_scale_factor     | 0.1
>  autovacuum_analyze_threshold        | 50
>  autovacuum_freeze_max_age           | 200000000
>  autovacuum_max_workers              | 3
>  autovacuum_multixact_freeze_max_age | 400000000
>  autovacuum_naptime                  | 60
>  autovacuum_vacuum_cost_delay        | 20
>  autovacuum_vacuum_cost_limit        | -1
>  autovacuum_vacuum_scale_factor      | 0.2
>  autovacuum_vacuum_threshold         | 50
>  autovacuum_work_mem                 | -1
>  log_autovacuum_min_duration         | -1
>
>
> Test 1: 55G    /srv/main
> TPS:    955
>
> Test 2: 112G    /srv/main
> TPS:    531 (Not sure what happened here, long checkpoint?)
>
> Test 3: 109G    /srv/main
> TPS:    868
>
> Test 4: 143G
> TPS:    840
>
> Test 5: 154G
> TPS:     722
>
> I am running the query here:
>
> https://wiki.postgresql.org/wiki/Index_Maintenance#Summarize_keyspace_of_a_B-Tree_index 
>
>
> And will post a followup. Once the query finishes I am going to launch 
> the tests with autovacuum_vacuum_cost_limit of 5000. Is there anything 
> else you folks would like me to change?
>
>
>
>

I usually advise setting autovacuum_naptime = 10s (or even 5s) for 
workloads that do a lot of updates (or inserts + deletes) - as on modern 
HW a lot of churn can happen in 1 minute, and that just makes vacuum's 
job harder.

regards
Mark