Re: odd postgresql performance (excessive lseek)

On Tue, Oct 19, 2010 at 10:36 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Jon Nelson <jnelson+pgsql(at)jamponi(dot)net> writes:
>> This is another situation where using pread would have saved a lot of
>> time and sped things up a bit, but failing that, keeping track of the
>> file position ourselves and only lseek'ing when necessary would also
>> help.
>
> No, it wouldn't; you don't have the slightest idea what's going on
> there.  Those lseeks are for the purpose of detecting the current EOF
> location, ie, finding out whether some other backend has extended the
> file recently.  We could get rid of them, but only at the cost of
> putting in some other communication mechanism instead.

I don't get it. Why would be doing that in a tight loop within a
single backend?

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company