Tuning for PostGreSQL Database

Christopher Weimann csw at k12hq.com
Thu Jul 24 10:39:15 PDT 2003

On Wed 07/23/2003-11:55:25PM -0700, Terry Lambert wrote:
> > The question I have is: can pages in the inactive queue be used as disk
> > cache?
> The answer is "yes, they can be reactivated and written to before
> they are flushed if soft updates is enabled" and "yes, they can be
> reactivated and read (but not written) to before they are flushed
> if soft updates is not enabled".
> In general, this only happens for data pages, which is to say, the
> pages containing user file data.  Pages containing FS metadata are
> specifically considered as "write through" or "virtually write
> through".
> It doesn't happen for data pages, if they are explicitly fsync'ed
> to ensure write ordering is guaranteed.

So if PostGreSQL uses fsync when writing ( which I think is only true
on the write-ahead logs at this point ) that data will NOT wind up in 
the cache.  Anything that PostGreSQL reads should wind up in the cache?

#uname -r

# top -b | head -5
last pid: 58622;  load averages:  1.96,  1.67,  1.47  up 2+12:59:15    13:31:39
130 processes: 6 running, 124 sleeping

Mem: 348M Active, 2628M Inact, 438M Wired, 155M Cache, 380M Buf, 76M Free
Swap: 4096M Total, 28K Used, 4096M Free

The 2628M Inact is likley to be acting as cache?

Basically I should stop worrying about this :)

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