Re: When do vacuumed pages/tuples become available for reuse?

On 04/11/2019 07:04 PM, Alvaro Herrera wrote:
> On 2019-Apr-11, rihad wrote:
>
>> On 04/11/2019 06:41 PM, Alvaro Herrera wrote:
>>
>>> Perhaps it'd be better to vacuum this table much more often.
>>>
>> Each run took 5-6 hours, now it takes 2-3 hours after I've tweaked some
>> cost-based vacuum knobs.
> But how often does it run?
>
One after another. Enough n_dead_tuples accumulate in between runs to 
easily trigger that.

autovacuum_vacuum_scale_factor = 0.01

utovacuum_vacuum_threshold = 50

which means to run autovac when 1% of table size + 50 rows have been 
updated or deleted.

But we can't make each autovacuum run run faster )

Currently I lowered this from 20ms:

autovacuum_vacuum_cost_delay = 10ms

And increased this from 200:

autovacuum_vacuum_cost_limit = 400

to make it finish in 1 hour rather than 3 hours.

Anything more than that and we risk impacting the performance of user 
queries.