Re: vacuum, performance, and MVCC

Hannu Krosing wrote:
> > > But we still have to think about similar cases (index entries pointing
> > > inside CITC chains), unless we plan to disallow adding indexes to
> > > tables.
> >
> > CREATE INDEX has to undo any chains where the new indexed columns change
> > in the chain, and add index entries to remove the chain.
>
> Yes, that would be the most straightforward solution.
>
> It could be better in some cases, if we could avoid adding entries to
> other indexes. Maybe we can just reset some flags, so that some SITC ops
> like finding tuples by the CITC index pointer still work while adding
> new entries wont.
>
> But it will be tricky to make this work for bitmap index scans.
>
> So yes, index build is a slop operation anyway, so making it even a
> little slower is probably not a big problem. And most CITC chains will
> have only one visible row at a time, this will probably not be a big
> issue.

Consider that index scans coming from different indexes have to span the
same SITC. I see no clean way to avoid making all the indexes
consistent, and as you said, CREATE INDEX isn't a frequent operation.

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +