Re: FSM search modes

On Fri, 2009-09-18 at 10:47 +0900, Itagaki Takahiro wrote:
> Simon Riggs <simon@2ndQuadrant.com> wrote:
> 
> > * compact - page selection specifically attempts to find the lowest
> > numbered blocks, so that the table will naturally shrink over time.
> 
> We cannot shrink the table if one tuple remains at the end of table
> and the tuple is always HOT-updated, because we put a new tuple into
> the same page where the old tuple is placed if possible.
> 
> In addition to your intelligent FSM search modes,
> do we need another algorithm to make the compaction to work better?

Perhaps we can have an additional piece of information about a table.
Something like target_size, so that normal updaters that attempt HOT
updates on blocks greater than target_size would know to avoid that
block and to seek a new location for the row lower in the table. Perhaps
such information could be reset and then sent via invalidation
mechanisms.

I'm thinking along the lines of a "fire alarm". An occasional mechanism
by which we can inform users of the need to evacuate certain blocks.

-- Simon Riggs           www.2ndQuadrant.com