[Bizgres-general] Off-list Re: [ENG] Re: Statement Queuing take II - Resource Scheduling (Running with cost and cursors)

[Mark Kirkwood]

Luke Lonergan wrote:
> Mark wrote: 
>
>  
>   
>> However I still think that even with no real memory pressure, 
>> that while this could help the *sort* step, it may hurt  row 
>> retrieval - as each query time slice may see a completely 
>> cold cache (from previous mail - assuming the actual database 
>> size > RAM, and each of the K queries scanning dataset is > 
>> RAM/K, not unreasonable assumptions for DSS and queries whose 
>> sort sets are large).
>>     
>
> For (scans >> RAM), cache is irrelevant.
>
>
>   

Thinking about this a bit more - and generating a bit more noise on this 
thread :-o , in this case the slicing might actually *help* a bit, as it 
would have a similar effect on IO scheduling for database files 
themselves (i.e fewer concurrent readers).  Of course there are many 
subtle effects that could nullify this (plan types that re-read their 
recent input and are therefore helped by caching - which slicing 
*hurts*) and environmental factors (statements from other queues hitting 
the same database files and spoiling the possible gains).

Cheers

Mark