Re: Some thoughts about i/o priorities and throttling vacuum

Andrew Sullivan wrote:

> On Fri, Oct 17, 2003 at 07:04:45PM +0530, Shridhar Daithankar wrote:
> 
>>I am slightly confused here. IIRC pg_autovacuum never did a vacuum full. At 
>>the most it does vacuum /vacuum analyse, none of which chew disk bandwidth. 
> 
> 
> The latter is false.  VACUUM FULL certainly uses _more_ disk
> bandwidth than VACUUM, but it's just false that plain VACUUM doesn't
> contend for disk.  And if you're already maxed, then that extra
> bandwidth you cannot afford.

What part of plain vacuum takes disk bandwidth? WAL? Clog? Certainly not data 
files themselves, right?

OK, I understand some system can be saturated enough to have additional WAL/Clog 
burdon, but genuinely curious, how much disk bandwidth is required for plain 
vacuum and what are the factors it depends upon?
 Shridhar