Re: 2nd Level Buffer Cache

Rados*aw Smogura<rsmogura@softperience.eu> wrote:
 
> I have implemented initial concept of 2nd level cache. Idea is to
> keep some segments of shared memory for special buffers (e.g.
> indices) to prevent overwrite those by other operations. I added
> those functionality to nbtree index scan.
> 
> I tested this with doing index scan, seq read, drop system
> buffers, do index scan and in few places I saw performance
> improvements, but actually, I'm not sure if this was just "random"
> or intended improvement.
 
I've often wondered about this.  In a database I developed back in
the '80s it was clearly a win to have a special cache for index
entries and other special pages closer to the database than the
general cache.  A couple things have changed since the '80s (I mean,
besides my waistline and hair color), and PostgreSQL has many
differences from that other database, so I haven't been sure it
would help as much, but I have wondered.
 
I can't really look at this for a couple weeks, but I'm definitely
interested.  I suggest that you add this to the next CommitFest as a
WIP patch, under the Performance category.
 
https://commitfest.postgresql.org/action/commitfest_view/open
 
> There is few places to optimize code as well, and patch need many
> work, but may you see it and give opinions?
 
For something like this it makes perfect sense to show "proof of
concept" before trying to cover everything.
 
-Kevin