Re: MMAP Buffers

On 15.04.2011 13:32, Radosław Smogura wrote:
> If I may, I want to share some concept to use mmap in PG. It's far, far
> away from perfect, but it's keeps WAL before data. As well I crated
> table, with index, inserted few values, and I done vacuum full on this
> table. Db inits welcome from orginal sources.
>
> Performance of read (if backend is loaded) is really good, query time
> goes down from 450ms to about 410ms. Update may be slower - but work is
> in progress (I will start with write, as I went to point when simple
> updates may be performed). Even that I didn't covered all aspects off
> updating, it's simple to do it, just to call PreopareBufferToUpdate
> before modifing buffer, ofc some ideas of increasing this are still in
> my head.
>
> Any comments, suggestions welcome.

The patch is quite hard to read because of random whitespace changes and 
other stylistic issues, but I have a couple of high-level questions on 
the design:

* Does each process have its own mmappings, or are the mmapping done to 
shared buffers?

* How do you handle locking? Do you still need to allocate a shared 
buffer for each mmapped page?

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com