[askdba] Re: Need help with Interview Questions

  • From: Nisar Tareen <ntareen@xxxxxxxxx>
  • To: askdba@xxxxxxxxxxxxx
  • Date: Mon, 8 Nov 2004 06:34:27 -0800 (PST)

irfan, 
I do not what to challenge your knowledge or comment,   My question will be 
that with the disk buffers in Database and  DISK BUffer  itself on disks  Plus 
RAID  Technology, do you think  the parallelision of disk multiple extents is 
in DBA's  hand. 

I will say the technology dictate that point and extra oradinary multiple 
extents is a liability to a system for write and read, i.e. "multiple hits" .

My two cent, my logic. 

Nisar Tareen 

 

 


 

Irfan Khan <irfan.khan@xxxxxxxxxxxx> wrote:
Hi rajesh

I can recall one pro for having multiple extent, is that at times, it =
can give u good performance with high degree of chances for parallelism

Regards
Irfan Khan

-----Original Message-----
From: Rajesh Puneyani [mailto:rajpuneyani@xxxxxxxxx]
Sent: Saturday, November 06, 2004 5:02 AM
To: askdba@xxxxxxxxxxxxx
Subject: [askdba] Re: Need help with Interview Questions


Thank you very much Ganesh and Todd.
Your responses gave me a very clear understanding of those questions.

I might shoot more questions as and when I appear in more interviews.

Regards
Rajesh

On Fri, 5 Nov 2004 08:11:02 -0500, Pepling, Todd C. =
wrote:
> See inline.
>=20
>=20
>=20
> > -----Original Message-----
> > From: Rajesh Puneyani [mailto:rajpuneyani@xxxxxxxxx]
> > Sent: Thursday, November 04, 2004 5:52 PM
> > To: askdba@xxxxxxxxxxxxx
> > Subject: [askdba] Need help with Interview Questions
> >
> >
> > Hi Guys,
> >
> > Recently I appeared in an interview for a position (after a long
> > time), Here are a few questions that got me confused.
> >
> > Pls. give me your feedback regarding the same.
> >
> > 1. What are various ways to create a table in one database from
> > another database ?
> > I would say - Create table as select (over the database link) and
> > Export/Import in Table mode.
> >=20
> > Any other ?
>=20
> I'm guessing they were looking for "copy", as in
>=20
> COPY FROM scott/password@DB01
> CREATE STUDENT (STUDENT_ID, STUDENT_NAME)
> USING SELECT ROLL_NO, NAME FROM STUDENTS
> WHERE CLASS_ID =3D 12;
>=20
> >
> > 2. If a table has 30 Uniform Extents (no size specified) then under
> > what circumstances it is good or bad ? Basically - What is the
> > advantage of 30 extents over 1 big large extents and what are the
> > minuses ?
>=20
> Pros for 30 uniform extents:
> 1) reduce wasted space and fragmentation at datafile/tablespace
> level
> 2) compatible with locally managed tablespaces
> 3) if even multiple of OS page size, can improve IO performance
>=20
> Pros for single large extent:
> 1) A single large extent can reduce time to execute
> ceratin DDL operations (i.e. truncate table), but
> highly unlikely you'd notice any difference compared
> to a 30 extent segment.
> 2) can reduce time needed to extend segment if initial extent
> is sufficient to hold entire segment throughout its life
> (as often is the case in "fact" or "reference" tables)
> 3) can reduce chaining
>=20
> >
> > 3. What are various scenarios which make RMAN the best backup and
> > recovery tool ?
>=20
> 1) large DBs (i.e. 1 terabyte) with limited backup window/time
> 2) DB refreshes/cloning
> 3) validating backed-up files are usable in recovery without
> actually trying a recovery
> 4) RMAN is "self-managing", but I've seen it puke on recovery,
> so it needs help
> 5) automatically purges old archivelogs
>=20
> I will point out that if your database is made of many 1G files
> instead of fewer 8G files, a recovery with RMAN can actually be
> slower that a traditional recovery. Also RMAN had enough bugs
> in 8i that it sometimes would fail to recover, while other times
> it would work. It seems to work fine in 9i.
>=20
> >
> > 4. what errors did u hit in your most recent DB Recovery procedure =
?
>=20
> A refresh via cloning is a recovery. Personally I've come across
> missing archivelogs, which RMAN would verify/validate during a
> backup, thus elliminating the missing archivelog issue. This ties
> into your question above.
>=20
> -Todd
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>=20
>



                        
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