Re: Question about PG cache selection strategy

[Jim Nasby <decibel(at)decibel(dot)org>]

On Nov 23, 2006, at 8:37 AM, Sefer Tov wrote:
> oddities. Clearly the caching algorithm favors caching the indices  
> to data (since they are more frequently accessed) but there is  
> another case where *recently written* entries are often requested  
> shortly after and I am not sure that they get prioritized correctly  
> by the cache. My question is whether the cache algorithm caches  
> only READ pages or also WRITTEN pages?
> If it does, is there to set some prioritization ratio for these per  
> table? It would enable to tune the caching for everyone specific  
> needs (if needed).

Any writes to a page happen via shared_buffers, so yes, writes are  
cached. Once a page is dirtied, it will stay that way until it's  
written out by the background writer, or a checkpoint writes it out.  
I believe that the buffer management algorithms can decide that page  
should be removed from the buffer, which would also write it out.
--
Jim Nasby                                            jim(at)nasby(dot)net
EnterpriseDB      http://enterprisedb.com      512.569.9461 (cell)