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

Matthew T. O'Connor wrote:

> On Fri, 2003-10-17 at 10:25, Shridhar Daithankar wrote:
> 
>>OK. So here is what I understand. I have a table which contains 100 rows which 
>>appeated there due to some insert operation. Then I vacuum it. And sit there for 
>>internity for rest of the database to approach the singularity(the xid 
>>wraparound..:-) Nice term, isn't it?).
>>
>>So this static table is vulnerable to xid wraparound? I doubt.
> 
> 
> No that table would probably be ok, because you did a vacuum on it after
> the inserts.  The problem is that pg_autovacuum may choose not to do a
> vacuum if you didn't cross a threshold, or someone outside of
> pg_autovacuum may have done the vacuum and autovac doesn't know about
> it, so it can't guarantee that all tables in the database are safe from
> xid wraparound.  
> 
> One additional thing, some of this might be possible if pg_autovacuum
> saved its data between restarts.  Right now it restarts with no memory
> of what happened before.  

Well, the unmaintened gborg version adopted approach of storing such info. in a 
table, so that it survives postgresql/pg_atuvacuum restart or both.

That was considered a tablespace pollution back then. But personally I think, it 
should be ok. If ever it goes to catalogues, I would rather add few columns to 
pg_class for such a stat. But again, thats not my call to make.

  Shridhar