Re: Extents and Fragmentation
Exactly what I was trying to say :) ----- Original Message ----- From: "Mark D. Stock" <mdstock@mydas.freeserve.co.uk> To: "Clifton M. Bean" <cmbean@home.com> Cc: <informix-list@iiug.org> Sent: Tuesday, June 20, 2000 4:52 PM Subject: Re: Extents and Fragmentation > "Clifton M. Bean" wrote: > > > > When you load a table from scratch, the first extent size is basically > > ignored since the data will be loaded continguously. If you fill one chunk > > and hope to another, each will be considered one extent. With such a large > > table, you might want to either load it into one multiple drives (one > > dbspace, multiple chunks) (round robin) or fragment it by expression > > (multiple dbspaces). > > That is true, but remember that those 212 extents still need to be > allocated, albeit appended to the first. Also, extent doubling will kick > in at some point, just to add to the overhead. With some home work up > front, the overhead of those extent allocations can be eliminated by > sizing the first extent correctly. For large tables, that overhead can > provide for a saving. > > Also, as this table will end up in at least two extents (3 Gb) spanning > two chunks, the next extent size becomes even more important. You can go > as far as setting both extent sizes to 2 Gb for the load. You can always > reduce the next extent size after the load with an ALTER TABLE command. > This of course depends on your sizing exercise. You don't want to > allocate 2 Gb unnecessarily, but you get the idea. > > > "Carlson@WHSmith" <carlson1@bellsouth.net> wrote in message > > news:642A954DD517D411B20C00508BCF23B00124AE6F@mail.sauder.com... > > > duffybj1@my-deja.com wrote: > > > > > > > > Hi guys, > > > > > > > > > > Hi > > > > > > > I'm a pretty new DBA, so if I sound ignorant, forgive me. > > > > > > We were all ignorant at one time . . . . some of us still are . . .. 8-) > > > > > > > > > > > In one of my busiest databases, we have a 40 million row table with 212 > > > > extents (about 3 MB)and several 4-10 million row tables with close to > > > > 200 extents. From what I read read in the past two weeks, this is a > > > > very bad thing. > > > > > > Ouch . . . you _did_ say 212 extents? That's somewhere between "bad" > > > and "I can't allocate any more extents" bad. > > Cheers, > -- > Mark. > > +----------------------------------------------------------+-----------+ > | Mark D. Stock mailto:mdstock@mydas.freeserve.co.uk |//////// /| > | http://www.informix.com http://www.informixhandbook.com |///// / file://| > | http://www.iiug.org +-----------------------------------+//// / ///| > | |This email will self-destruct in |/// / ////| > | |10 sec. If you received this email |// / /////| > | |in error, sorry about the mess. |/ ////////| > +----------------------+-----------------------------------+-----------+ > > >