Re: Redo Log Question

Mistakes we all make. Me just as much as anyone (see posts passim).

Statements from the Gospel with the Authority of il Papa which turn out to be nothing more than a bunch of garbage, a different matter, I think.

Put it this way: we have both dealt with students who are denser than Osmium. Do I criticise them for that? Nope. I spend more time with them as a result. It's not their fault, and we hope they'll learn, and I do my damndest to make sure they do. But if I knew nothing about X, would I go on a newsgroup and proclaim I knew all about X? Would I set out to mislead newbies that my way was correct? Nope.

Check out Google for my name and SQL Server, as a for-example.

This guy didn't make a mistake. He made an error, and when that was pointed out to him, complained about the attitude of the person pointing his error out to him. And then proceeded to duck and weave, as though clinging on to a soupçon on truth in a miasma of error. Mistakes you back out from. Wilful ignorance you cling on to for grim death.

Wilful ignorance I won't put up with. In the classroom as much as here.

But whatever: Merry Christmas to you and yours. And I know you need to be handled carefully. I saw you after the last Xmas party, remember!!

HJR "Richard Foote" <richard.foote_at_bigpond.com> wrote in message news:8wSN9.9171$jM5.25781_at_newsfeeds.bigpond.com...
> Hi Howard,
>
> The next time I make a mistake (which won't be too long I'm sure), please
be
> gentle.
>
> I'm very fragile and need to be handled carefully.
>
> Please ;)
>
> Merry Xmas !!
>
> Richard
> "Howard J. Rogers" <howardjr2000_at_yahoo.com.au> wrote in message
> news:ruRN9.9139$jM5.26326_at_newsfeeds.bigpond.com...
> >
> > "Burt" <burtpelt_at_bellsouth.net> wrote in message [snip]
> >
> > > > > I have been doing Oracle server DBA support for about 10 years.
> > > > >
> > > >
> > > > Badly, by the sounds of it.
> > >
> > >
> > > Today has been a busy day, but I had to comment one more time...
> > >
> > > You still have an attitude problem. And, you don't consider the above
> > > comment an insult ?
> > >
> >
> > No I don't. If you've been managing a database for 10 years based on the
> > level of knowledge you've exhibited in this thread, then I fear for your
> > database.
> >
> > No: a personal insult would be saying things like 'your attitude sucks'.
> >
> > You know, personal stuff. Based on no knowledge of the person concerned,
> but
> > just because you happen to disagree with the person involved.
> >
> > The only comments I have passed have been based on your demonstrated
> > knowledge of a subject on which you thought yourself fit to comment.
> >
> > > If in your opinion, I said 1 thing in error, then does that mean I do
> > > my job badly ? You have no idea.
> > >
> >
> > You said, without qualification, that Oracle recommended X when actually
> it
> > recommended Y. I pointed that out to you. You at that point had the
chance
> > to say 'my mistake, I'm sorry, thanks for the enlightenment'. But no.
You
> > decided instead to suggest that it was *my* attitude that was the
problem.
> > So no, I have no idea, except that you are someone who appears to know
not
> > very much, but will defend to the death his right to say crap.
> >
> > > I don't care how much you know about Oracle, I wouldn't want to work
> > > with you.
> > >
> >
> > Fair enough. I'd sack you anyway.
> >
> > > Just because you aren't face-to-face, you think you can insult anyone?
> > > You don't sound like you work too well in this environment.
> > >
> >
> > Strangely enough, I post with my actual email address and my own name. I
> > have absolutely no problem taking this offline and dealing with it
there.
> >
> > Get over it, anyway: I didn't insult you. I said you didn't know very
much
> > about Oracle. You don't. Thems the facts. Deal with it.
> >
> > > >
> > > > > The comment about "Oracle recommends" comes out of a white paper
> from
> > > > > Oracle or from the docs . I don't have the time to check it. But,
it
> > > > > is there. Search Metalink and docs if you have the time.
> > > >
> > > > Please see below.
> > > >
> > > > > So, if the OS can mirror corruption, why wouldn't Oracle mirror it
> > > > > too? I have SEEN BOTH (how about you?) the OS AND Oracle mirror
> > > > > "software" corruption.
> > > >
> > > > Because with OS mirroring, you have LGWR only writing once, and then
> > that
> > > > being copied by the OS to the mirror. One write. One stuff up. One
> > > > corruption. Mirrored. With multiplexing, LGWR writes twice (or three
> > times,
> > > > if you do 3-way multiplexing). With two (or more) writes, it is
> highly
> > > > unlikely that LGWR would introduce the same corruption at the same
> point
> > in
> > > > the redo stream. Therefore, multiplexing protects you against
software
> > > > corruption.
> > > >
> > >
> > >
> > > I lost all faith in Oracle doing the 2nd write better than the OS when
> > > I had to do the recover mentioned below. Maybe your experience is
> > > better. But, my experienced recover in version 7.3.2.3 shows that
> > > Oracle does/did indeed mirror software corruption that Oracle
> > > introduced.
> > >
> > > My first choice "with unlimited budget" would be to both multiplex and
> > > OS mirror.
> > >
> >
> > That's not what you originally said, where you expressed a preference
for
> OS
> > mirroring, said that Oracle Corporation supported you in expressing the
> > same, and suggested that multiplexing was an optional extra.
> >
> > > Now, I cannot find that paper. I know I have a hardcopy in my office,
> > > but I won't be there for a couple of weeks.
> > >
> >
> > I shan't hold my breath. I've quoted you the documentation. Anything
else
> is
> > likely to be irrelevant.
> >
> > > But, I see now in a quick check on Metalink that there is a consensus
> > > that the 1st choice is multiplexing. Interesting... I know I didn't
> > > imagine the paper from Oracle recommending OS mirroring first.
> > >
> > > Anyway, I have had some good luck with OS mirroring and the above
> > > mentioned bad luck with Oracle multiplexing.
> > >
> >
> > Luck isn't science. Good DBAing is about science.
> >
> > >
> > >
> > > > >
> > > > > > If Junior DBA is practising his Unix skills, and issues an 'rm
*'
> > > > command,
> > > > > > then the OS faithfully deletes the mirrored copy of the redo log
> as
> > well
> > > > as
> > > > > > the original. Result: a totally missing redo log group.
> > > > > >
> > > > >
> > > > > I don't let junior DBAs touch my systems :)
> > > > >
> > > > > BTW, did you notice my comment about "debating this one". Hmmm ,
> > > > > probably not.
> > > > >
> > > >
> > > > Yes, and you missed the point: there's nothing to debate. Oracle
does
> > not
> > > > recommend OS mirroring as its first line of defence. Period.
> > > >
> > > > >
> > > > > > Oracle multiplexing, by contrast, protects you from both these
> > > > scenarios,
> > > > >
> > > > >
> > > > > Uhh ? Why wouldn't Oracle put the same damn corruption in both
> > > > > copies?
> > > >
> > > > Because, with multiplexing, LGWR has to write twice. With O/S
> mirroring,
> > it
> > > > writes once and then the O/S is responsible for making the copy.
> > > >
> > > > The chances of LGWR introducing corruption at exactly the same spot
> with
> > two
> > > > different writes is pretty small.
> > >
> > >
> > >
> > > Apparently not impossible since that IS what occurred in my experience
> > > noted below.
> > >
> >
> > Of course it's not bloody impossible! What do you want? Guarantees
signed
> in
> > blood? The question -the REAL question- is which is MOST LIKELY to
prevent
> a
> > problem. A single write mirrored by the OS or multiple LGWR writes. It's
a
> > question of probabilities, and the answer isn't hard to come by.
> >
> > >
> > >
> > > >
> > > > >It did it to me once in version 7.3.2.3 and I spent the next
> > > > > 27 hours recovering. Corruption got in the datafile and REDO logs
> and
> > > > > was also archived. We (myself and an Oracle analyst at Oracle
> support)
> > > > > didn't know for sure when the corruption occurred. Got lucky doing
a
> > > > > point-in-time recovery with a guess.
> > > > >
> > > >
> > > > Fascinating stuff. But not relevant, is it?
> > > >
> > >
> > > See above comment.
> > >
> > >
> > > > >
> > > > > > and can also protect you from hardware (disk) failure, since
each
> > member
> > > > is
> > > > > > supposed to be housed on a different disk.
> > > > > >
> > > > > > >
> > > > > > > 2) The 2nd choice is to use Oracle's "mirroring" by specifying
a
> > 2nd
> > > > member
> > > > > > > in each REDO group.
> > > > > > >
> > > > > > > 3) If you use OS mirroring, you shouldn't need the Oracle
> > mirroring
> > > > and
> > > > the
> > > > > > > opposite is true too.
> > > > > > >
> > > > > >
> > > > > > Total and complete bollocks, I'm sad to say. They are
> complementary,
> > but
> > > > > > your first choice should be Oracle multiplexing. By all means
then
> > > > hardware
> > > > > > mirror, too. But multiplexing should be regarded as compulsory.
> > > > > >
> > > > >
> > > > > I appreciate your paranoid attitude. You have to be a little
> paranoid
> > > > > to be a server DBA :) I would admit in a "perfect" world, I would
> > > > > want 4 disks for REDO logs for EVERY database. Really, though, not
> all
> > > > > installations have the option of using 4 disks for REDO logs.
> > > > > Sometimes, you are limited .
> > > > >
> > > >
> > > > Then compromise by combining data files on what few disks you have
and
> > > > suffering a performance hit. But don't compromise the safety of your
> > data by
> > > > not multiplexing.
> > > >
> > >
> > > Maybe my attitude on Oracle mirroring/multiplexing could use an
> > > update.
> >
> > It certainly could.
> >
> > >As I said above, I lost all faith in Oracle mirroring during
> > > the recover mentioned above.
> > >
> >
> > It's not even called 'Oracle mirroring". It's called multiplexing.
> > Precision, dear. Precision.
> >
> > >
> > > > > We also have a lot of SysAdmin types who think all Oracle files
> > > > > should/could go on 1 RAID disk ... nuts. Anyway, purchases are
made
> > > > > without talking to DBAs sometimes too. Stuff happens.
> > > > >
> > > > >
> > > > > > Thus speaks an Oracle instructor, incidentally, so where you get
> the
> > > > idea
> > > > >
> > > > > I once had an Oracle instructor tell me in an Oracle7 application
> > > > > tuning class that the CBO would ALWAYS make a better performance
> > > > > choice over the RBO.
> > > > >
> > > > > YEAH, sure.
> > > > >
> > > >
> > > > I smell a strawman. What some instructor told you in years gone by
> about
> > > > optimization of SQL has nothing to do with the issue at hand.
> > > >
> > >
> > > You mentioned first "Thus speaks an Oracle instructor" . I was only
> > > pointing out that doesn't always guarantee it.
> >
> > Do your research, then. This Oracle instructor has been posting
regularly
> to
> > this newsgroup for 3 years. He's learnt lots, and corrected himself more
> > than a few times. But can't stand idiots posting utter bullshit on
things
> he
> > actually knows something about.
> >
> > >
> > > > > This goes to show you all instructors don't always know what the
> heck
> > > > > they are talking about.
> > > > >
> > > >
> > > > This goes to show you that *an* instructor bought the marketing
spiel
> of
> > > > Oracle 7. It says nothing about the merits or otherwise of
> multiplexing
> > > > and/or mirroring.
> > > >
> > > > > Of course, that is just one in my 10 to 15 classes on Oracle, so
> that
> > > > > isn't bad for Oracle.
> > > > >
> > > >
> > > > It took you that many?
> > > >
> > >
> > > Oracle6 Introduction
> > > Oracle6 DBA I
> > > Oracle6 DBA II
> > > Oracle6 CASE Tailored Class
> > > Oracle7 DBA I
> > > Oracle7 DBA II
> > > Oracle7 Application Tuning
> > > Oracle7 Server Tuning
> > > Oracle8+8i New Features for DBAs
> > >
> > > Ok, so only 9. I suppose I was thinking of all the Unix type classes
> > > like Bourne programming, Pro*C, etc. .
> > >
> >
> > "Of course, that is just one in my 10 to 15 classes on Oracle".
> >
> > "Ok, so only 9".
> >
> > Come off it. Post facts, please. Be precise, factual and accurate. 10 to
> 15
> > suddenly becomes 9?????
> >
> > And you have the gall to question MY attitude?
> >
> > > > >
> > > > > > the "Oracle" as an entity recommends one approach over the
other,
> I
> > have
> > > > no
> > > > > > idea.
> > > > > >
> > > > >
> > > > > In a white paper off Metalink ... maybe I'll have time another day
> to
> > > > > dig it up for you.
> > > > >
> > > >
> > > > Don't bother. Here's the documentation:
> > > >
> > >
> > > Yeah, this appears to be the latest.
> >
> > It doesn't appear to be the latest. It *is* the latest.
> >
> > [snip]
> > > > >
> > > > > You ever tried to do an "ls" command on a directory with 1000's of
> > > > > files ... pipe it to grep and you get strange errors... scripts
> start
> > > > > failing ... etc.
> > > > >
> > > >
> > > > So, manage the archive destination properly.
> > > >
> > >
> > > Yeah, don't make the log too small right ? Of course, clean up after
> > > backing up twice too.
> > >
> >
> > Don't be ridiculous. Clean up when it is suitable to 'clean up' if by
> 'clean
> > up' you mean deleting archive logs. I sincerely hope you don't think
that
> > because you've backed up twice you can delete all prior archives without
> > compunction.
> >
> > > >
> > > > > And too large, impacts INSTANCE recovery.
> > > > >
> > > >
> > > > No. Too long an interval since your last checkpoint affects the time
> it
> > > > takes to perform an Instance recovery, not the size of your redo
logs
> > per
> > > > se. It is perfectly possible to have enormous online redo logs, and
> have
> > a
> > > > perfectly respectable instance recovery time. That's what
> > > > LOG_CHECKPOINT_INTERVAL, LOG_CHECKPOINT_TIMEOUT,
FAST_START_IO_TARGET,
> > > > DB_BLOCK_MAX_DIRTY_TARGET and FAST_START_MTTR_TARGET are all about.
> > > > Depending on your version.
> > > >
> > >
> > > Seems easier to just size the REDO at a good time for checkpointing,
> > > since checkpoints occur when the log switches.
> > >
> >
> > Yes, well. We know what you think easier: stating things which just
aren't
> > true.
> >
> > > Why complicate things when you can make them simpler?
> > >
> >
> > Because there are a rich variety of tools avialable to you to make sure
> that
> > instance recovery times are NOT dependent on the size of your online
redo
> > logs. So what's the point in pretending that size makes all the
> difference?
> >
> > > Does anyone really tweak these parameters?
> >
> > Er, yes actually. Good DBAs do.
> >
> > >I usually just set the
> > > interval real high to force checkpointing at log switch time.
> > >
> >
> > What you 'usually just set' and what is good practice might just happen
to
> > be two completely different things. Oh: and in this case, they just
happen
> > to be two completely different things.
> >
> > >
> > > > >
> > > > > > DBAs forever have to worry about the AMOUNT of redo generated,
> > because
> > > > an
> > > > > > archive destination that uses up all its available space is a
> > problem
> > > > > > waiting to happen: but that's a function of size, not of number.
> > > > > >
> > > > >
> > > > > And you didn't even mention since 8i you can have multiple
> > > > > destinations :)
> > > > >
> > > >
> > > > You can't even get this correct, either. Multiple destinations was
> > actually
> > > > introduced as a feature of 8.0, not 8i. LOG_ARCHIVE_DEST and
> > > > LOG_ARCHIVE_DUPLEX_DEST.
> > > >
> > >
> > > We skipped 8.0 .
> > >
> >
> > Uh huh. So that makes it alright to post to these newsgroups with
> statements
> > which are false, misleading and totally erroneous?
> >
> > I don't think so.
> >
> > >
> > [snip]
> > > > > My current newsgroup is not allowing me to post for some stupid
> > > > > reason. So, I use Google to post and my normal Bellsouth newsgroup
> to
> > > > > read.
> > > >
> > > >
> > > > Another total non sequitur. All newsgroup posts, made from wherever,
> are
> > > > archived at Google.
> > > >
> > >
> > > Again, you mentioned "such archives as Google". I was only pointing
> > > out that I don't use it normally.
> > >
> >
> > And I was pointing out that it doesn't matter one iota: Google will
> archive
> > you and the completely fallacious nonsense you posted, wherever you
posted
> > it from.
> >
> > >
> > > > Putting it bluntly, you may have been doing this stuff for 10 years,
> but
> > > > your knowledge and understanding are demonstrably weak, and your
> initial
> > > > statement that "Oracle's 1st recommendation is to use OS mirroring
for
> > REDO
> > > > logs" is totally untrue, as a cursory glance at the documentation
> would
> > have
> > > > shown you.
> > > >
> > >
> > > I might have spoke too soon with mentioning the phrase "Oracle
> > > recommends"
> >
> > Correction. You spoke too soon, erroneously, and without the slightest
> > scintilla of evidence to back you up. And you were wrong in any case.
> >
> > >, although I do have a paper from Oracle stating that .
> >
> > Can't wait for the evidence.
> >
> > > And, yes I lost faith in Oracle multiplexing back when I had to do the
> > > recover mentioned above.
> >
> > OK. I respect the fact that your experience has exposed you to recovery
> > scenarios I couldn't dream of. And you are entitled to your opinions as
a
> > result. What you are not entitled to do is post your opinions here (and
at
> > Google for the forseeable future) AS THOUGH THEY WERE FACT.
> >
> > You stated that Oracle advises X when in fact it advises Y. I pointed
out
> > that Oracle didn't advise X at all, and get a stream of abuse about my
> > 'attitude' as a result. When it comes to insults, you cast the first
> stone.
> >
> > If you could but admit that what you posted was your opinion, I'd back
off
> > immediately. Everyone's entitled to their opinion. Just don't pretend
that
> > your opinion (which on the physical facts is slightly dodgy anyway) is
> > factual or meaningful.
> >
> > I take absolutely zero pleasure in pointing out factual errors like
this.
> > But Oracle software is too good to let shit myths and opinions stuff up
> its
> > implementation. And the facts are too easily discernible to warrant the
> > dissemination of errors, at least in this particular area.
> >
> > As I said originally, I wish you a joyful Christmas and a happy new
year,
> > because I am not an ogre or a piss-artist, and actually care that anyone
> who
> > invests time and effort in Oracle should come up trumps.
> >
> > I hope we can move on from this and leave the world a wiser place.
> >
> > End of thread
> > HJR
> >
> >
> >
> > >Oracle put corruption in the REDO and
> > > mirrored it. I was multiplexing and it was useless.
> >
> >
> >
> >
> >
> >
> > >
> > > > Sorry you don't like my attitude, but those are just the facts.
> > > >
> > > > HJR
> >
> >
>
>
Received on Tue Dec 24 2002 - 00:16:38 CST