RE: Vacuum only with 20% old tuples

> -----Original Message-----
> From: Tom Lane [mailto:tgl@sss.pgh.pa.us]
> 
> "Hiroshi Inoue" <Inoue@tpf.co.jp> writes:
> >> Basically what I want here is to build the new index relation as
> >> a new file (set of files, if large) and then atomically commit it
> >> as the new version of the index.
> 
> > Hmm,your plan seems to need WAL.
> > We must postpone to build indexes until the end of tuple moving
> > in vacuum. Once tuple moving started,the consistency between
> > heap and indexes would be broken. Currently(without WAL) this
> > inconsistency could never be recovered in case of rollback.
> 
> Why?  The same commit that makes the new index valid would make the
> tuple movements valid.

Oops,I rememered I wasn't correct. Certainly it's not so dangerous as
I wrote. But there remains a possibilty that index tuples would point to
cleaned heap blocks unless we delete index tuples for those heap blocks.
Cleaned blocks would be reused by UPDATE operation. 

Regards.

Hiroshi Inoue