On Thu, 5 Jan 2006, Qingqing Zhou wrote:
>
> Feasibility: Our bufmgr lock rewrite already makes this possible. But to
> enable it, we may need more work: (w1) make bufferpool relation-wise,
> which makes our estimation of data page residence more easy and reliable.
> (w2) add aggresive pre-read on buffer pool level. Also, another benefit of
> w1 will make our query planner can estimate query cost more precisely.
>
"w1" is doable by introducing a shared-memory bitmap indicating which
pages of a relation are in buffer pool (We may want to add a hash to
manage the relations). Theoretically, O(shared_buffer) bits are enough. So
this will not use a lot of space.
When we maintain the SharedBufHash, we maintain this bitmap. When we do
query cost estimation or preread, we just need a rough number, so this can
be done by scanning the bitmap without lock. Thus there is also almost no
extra cost.
Regards,
Qingqing
