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

On 07/19/2017 07:57 PM, Tom Lane wrote:
> Peter Geoghegan <pg(at)bowt(dot)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?

JD

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