[askdba] Re: Need help with Interview Questions
- From: "Irfan Khan" <irfan.khan@xxxxxxxxxxxx>
- To: <askdba@xxxxxxxxxxxxx>
- Date: Fri, 5 Nov 2004 20:57:16 -0500
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. <tpepling@xxxxxxx> =
wrote:
> See inline.
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> > -----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.
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> > Any other ?
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> I'm guessing they were looking for "copy", as in
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> COPY FROM scott/password@DB01
> CREATE STUDENT (STUDENT_ID, STUDENT_NAME)
> USING SELECT ROLL_NO, NAME FROM STUDENTS
> WHERE CLASS_ID =3D 12;
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> >
> > 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 ?
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> 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
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> 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
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> >
> > 3. What are various scenarios which make RMAN the best backup and
> > recovery tool ?
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> 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
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> 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.
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> >
> > 4. what errors did u hit in your most recent DB Recovery procedure =
?
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> 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.
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> -Todd
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>
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