Re: Including Snapshot Info with Indexes

"Gokulakannan Somasundaram" <gokul007(at)gmail(dot)com> writes:

> I accept that the indexes will be bigger in size for this approach. You
> might need more disk-space and you might need more memory to accomodate the
> same amount of information. But i think disk costs and memory costs have
> come down a lot, People can afford to buy more disk and memory.

That's not how it works. We're not generally worried about people running out
of disk or memory resources. But no matter how cheap they get people will only
have what they have. We have to worry about running as fast as possible for a
*given* amount of RAM or disk.

Generally raising disk space usage results in a corresponding increase in run
time. So an index that takes twice as much space on disk will consume twice as
much time to consult as one that doesn't. You need to save enough time
elsewhere to make that up and then some to make it worthwhile.

I think we are pretty set on having the DSM for vacuuming purposes so you'll
also have to argue this approach will cover enough additional cases or be
better in some other way compared to using the DSM to be a win.

--
Gregory Stark
EnterpriseDB http://www.enterprisedb.com