Re: FSM search modes

On Oct 1, 2009, at 4:18 PM, Robert Haas wrote:

> On Thu, Oct 1, 2009 at 5:08 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Robert Haas <robertmhaas@gmail.com> writes:
>>> The elephant in the room here is that if the relation is a million
>>> pages of which 1-100,000 and 1,000,000 are in use, no amount of bias
>>> is going to help us truncate the relation unless every tuple on page
>>> 1,000,000 gets updated or deleted.
>>
>> Well, there is no way to move a tuple across pages in a user- 
>> invisible,
>> non-blocking fashion, so our ability to do something automatic  
>> about the
>> above scenario is limited.  The discussion at the moment is about  
>> ways
>> of reducing the probability of getting into that situation in the  
>> first
>> place.  That doesn't preclude also providing some more-invasive tools
>> that people can use when they do get into that situation; but let's
>> not let I-want-a-magic-pony syndrome prevent us from doing anything
>> at all.
>
> That's fair enough, but it's our usual practice to consider, before
> implementing a feature or code change, what fraction of the people it
> will actually help and by how much.  If there's a way that we can
> improve the behavior of the system in this area, I am all in favor of
> it, but I have pretty modest expectations for how much real-world
> benefit will ensue.  I suspect that it's pretty common for large


Speaking of helping other cases...

Something else that's been talked about is biasing FSM searches in  
order to try and keep a table clustered. If it doesn't add a lot of  
overhead, it would be nice to keep that in mind. I don't know where  
something like randomly reseting the search would go in the code, but  
I suspect it wouldn't be very expandable in the future.

But like Tom said, the top goal here is to help deal with bloat, not  
other fanciness.
-- 
Decibel!, aka Jim C. Nasby, Database Architect  decibel@decibel.org
Give your computer some brain candy! www.distributed.net Team #1828