Re: Equivalent praxis to CLUSTERED INDEX?

Mishca,

> Ummm ... not quite. In MSSQL/Sybase/Oracle, a clustered index maintains
> its space saturation as part of each update operation. High activity
> does indeed result in less-full pages (typically 60-80% full for tables
> with heavy deletions or rowsize changes). To bring the percentage back
> up, you run DBCC INDEXDEFRAG, which also does what you'd expect of a
> normal file defragmenter -- put related disk pages together on the platter.

Sure, it does now, which is a nice thing. It didn't in the first version
(6.5) where this cluster maint needed to be done manually and asynchronously,
as I recall.

> As for SQL Server being a 'single-user database' ... ummm ... no, I
> don't think so.

Hmmm ... perhaps it would be better if I said "serial-only database". MSSQL
(like earlier versions of Sybase) handles transactions by spooling everything
out to a serial log, effectively making all transcations SERIAL isolation.
This has some significant benefits in performance for OLAP and data
warehousing, but really kills you on high-concurrency transaction processing.

> I'm REALLY happy to be shut of the Microsoft world, but
> MSSQL 7/2000/2005 is a serious big DB engine. It also has some serious
> bright heads behind it. They hired Goetz Graefe and Paul (aka Per-Ake)
> Larsen away from academia, and it shows, in the join and aggregate
> processing. I'll be a happy camper if I manage to contribute something
> to PG that honks the way their stuff does. Happy to discuss, too.

Yeah, they also have very speedy cursor handling. I can do things with
cursors in MSSQL that I wouldn't consider with other DBs. Not that that
makes up for the lack of other functionality, but it is nice when you need
it.

--
--Josh

Josh Berkus
Aglio Database Solutions
San Francisco