RE: Extents: Reality and Myth
AIX has a 4K page size. So the maximum number of extents is higher than
for 2K ports. Mark Scranton provides a good explanation of this topic at
his
Web site: http://members.tripod.com/markscranton/informix/informix.htm
Look in the Monthly Topic Archive. It was discussed on "Jan 15, 1999".
-----Original Message-----
From: Doug Agnew [mailto:dagnew@charlottepipe.com]
Sent: Wednesday, March 15, 2000 7:06 AM
To: informix-list@iiug.org
Subject: Re: Extents: Reality and Myth
"Victor Glass" <vglass@mailbox.bellatlantic.net> wrote in message
news:38CF84F9.C095042E@mailbox.bellatlantic.net...
> I am in the process of re-sizing a database, and revisited the topic of
> extents. We are running IDS 7.30 UC7, RS/6000 w/8 cpus, AIX 4.3, and we
> use a disk volume manager. I've looked at FAQ and several books,
> including Joe Lumbley's "Informix - DBA Survival Guide". Given all this,
> I still have questions. Would someone please fill in the blanks, and
> them some:
>
> All this pertains to IDS 7.3X:
>
> 1.The maximum number of extents that a table can have is _____. (it
depends on how many indexes and special columns the table has. There is a
table definition page (tblspace tblspace) that holds all this info. When
full, it is all over for the table. The normal value is probably around
250....
> 2. If there is in fact a maximum number of extents, when that is reached
> the engine will ___________________________________. Don't know ---
suspect that table inserts will fail.
> 3. If the maximum number of extents is very very large (don't know this
> until someone answers question 1.), the benefits of minimizing the
> number of extents allocated is _____________________________________.
Well, it reduces the path length to determine which physical extent a
logical page is in.
> 4. If a dbspace is dedicated to a single table, that table will have one
> and only extent regardless of what extent size and next extent size is
> set to: ___ True ___ False. -- False --- if the dbspace extends to
multiple chunks, each chunk will require an extent. Also, if the dbspace
was not INITIALLY dedicated to the table, but now contains gaps where other
tables used to be, using those gaps will probably require an extent, since
an extent must be a contiguous set of logical pages.
> 5. Any Comments about extents, determining their size, etc:
To determine the extent size, use oncheck -pT (or -pt) to print the table
info. A list of all extents will be produced. You may want to consider
taking the 'internals' class. Excellent class that goes into a LOT of the
physical storage of the database.
>
> Any clarification will be helpful. No tap dancing please.
>
> Vic
>