Re: [Testperf-general] pg_autovacuum w/ dbt2

Mark Wong wrote:

>On Fri, Jan 07, 2005 at 10:13:52AM -0800, Josh Berkus wrote:
>  
>
>>Mark,
>>    
>>
>>>All default parameters.  Matthew also recommended using the
>>>vacuum_delay setting so I was about to try that.
>>>      
>>>
>>Interesting ... the default parameters are quite conservative, running only 
>>when the table has doubled in new rows.   So if those spikes are vacuums, 
>>then the DBT2 test is updating or adding 100% of the rows in the orders table 
>>every 6-8 minutes?    Does that seem right?
>>    
>>
>
>Some hand-wavey math here:
>
>We start with 18,000,000 rows in the orders table.
>
>Based one 3281 transactions per minute for just the new-order transaction:
>    288 transactions per minute for delivery
>
>New-order inserts 3281 rows per minute (not counting the 1% of rollbacks.)
>Delivery updates 288 rows per minute in orders.
>
>So no, we're not change that many rows per minute...
>  
>

Except the thing pg_autovacuum is actually doing is Analyzing the 
district table (4800 rows, takes ~15 sec) and vacuuming the warehouse 
table (66,000, takes ~50sec) which takes about 50 seconds.  Since the 
default vacuum sleep time is 5 minutes, that would explain the dip every 
6 minutes.

Matthew