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Re: Your opinion please :) explanation of my point of view

From: Juan Cachito Reyes Pacheco <jreyes_at_dazasoftware.com>
Date: Thu, 26 Feb 2004 08:48:16 -0400
Message-ID: <017701c3fc66$ce497450$2501a8c0@dazasoftware.com>


Thanks for your opinion, tellme what do you think, about this.

Point by point
1) About the set of checklist, I agree, but the goal is to introduce to tunning, in the market there are several excellent tunning books, (including the documentation where is almost all), but people don't read them. I decided something short, a checklist explaining very very briefly what you can tune, the most important, the first steps, for newbies, now if you want more information, you can go to documentation. For example about statistics, I had two pages of a BRIEF explanation, but no body is going to read all that, because instead of 8 pages it will be 60 pages, it will be preferable to read the documentation, but several questions you should had read some moment, shows people don't like to read, people who never took the time to read neither concept manual, so I decided to explain the most important, briefly.

For example, about statistics, the explanation is very short 1.1 Statistics
The optimizer works based on statistics, if they are old, or inaccurate you' ll get a wrong execution plan.

You must recalculate statistics every time an important change had happened in it:

Periodically, based on normal changes in a database

After importing a big amount of data

When distinct values in primary columns change

After creating indexes and table

1.1.1 Test database
If this is the first time you get statistics, you must remember some database has fixed execution plans, or any other consideration can cause a statistics recalculation cause serious problems, as general rule do it first in ha test database, before doing in the production database.

1.1.2 Recalculating statistics
Oracle recommends DON'T USE ANALYZE to gather statistics, the package USE DBMS_STATS, this package get more statistics, specially for new features.

Don't execute DBMS_STATS on SYS schema.

This command has dozens of options, like parallel execution, etc. etc. you must read them.

To gather all statistics

EXEC DBMS_STATS.GATHER_DATABASE_STATS(); To gather statistics in a schema:

EXEC DBMS_UTILITY.ANALYZE_SCHEMA('ADM','COMPUTE'); To gather statistics in a schema, more precisely, the one we use, because our database is a small database:

EXEC DBMS_STATS.GATHER_SCHEMA_STATS( OWNNAME=>'ADM', ESTIMATE_PERCENT=>100,METHOD_OPT=>'FOR ALL COLUMNS SIZE SKEWONLY'); What you understand after this is

-optimizer needs statistics
-changing statistics can cause you problems, first use a test database
-use dbms_stats not analyze

That's all, and I think this is the basic thing you have to understand, I know dbas (not ocps) who don't know that simple fact," they have to recalculate statistics periodically". Because their database are small and comparing with sql server it takes a similar amount of time to process, they don't see it as a problem or a mistake.

2)About the optimizer_index_caching I read a lot, because we have a problem, we solved setting this parameter, about this parameter I say: "This parameter sets the possibility to find blocks accessed through an index in memory.

Default value is 0, 0 means that no one block accessed through index will be found in memory THIS IS FALSE. A value of 90% is advisable"

Could you giveme an example how could I explain it better.

3) About
"but pays no attention to individual business processes (or indeed development modules)."
Could you giveme an example what for example I could add , But I'm not explaining in this paper things like ORDERED hint, because for a newbie, first he have to do the basic things, once he had done all of them, if he continue having problems, then the correct way is to read a more serious document.

Because if you give advanced points, he will try them first, is like special
hints, I think you heard about them, they are not in documentation because
it could cause problems to new dbas, because they could try to use them to
solve problem, when the reality is they can be used only exceptionally. but there are book out there once you get the enough experience you could buy them.

Now if you want another point of view, or a better idea about this, you are welcome :).

hi

I have to admit I don't like the paper much. it looks like a set of checklists with little or no reasoning behind them. for example the suggestions on optimizer_index_caching have just start at x and work from there. where x is apparently an arbitrary number.

my deeper problem is that the article seems to suggest that it is possible to tune systems but pays no attention to individual business processes (or indeed development modules). I disagree, the logical unit for tuning is the thing that runs badly, the logical time to do it is when writing the code for it. setting db wide parameters is sticking plaster on the titanic. perhaps.

Niall

-----Original Message-----
From: AC.GWIA.oracle-l_at_freelists.org [mailto:AC.GWIA.oracle-l_at_freelists.org] Sent: Wed 25/02/2004 18:41
To: jreyes_at_dazasoftware.com; oracle-l_at_freelists.org Cc:
Subject: Your opinion please :)

Hi I took sometime to do a paper, to help newbies in tunning, this is not to become they expert, but at least they know there are statistics in the database

If you get some time, and give some opinion about it, like the previous mistake I did with IN function, you are welcome. Or something important I'm missing (for newbies dbas of course). Did you remember the first time you had a tunning problem, before the ocp, and you didn't knew where to start to check,and lost long time, changing some database parameter to see if that improved something, the idea is to save that step.

http://www.geocities.com/juancarlosreyesp/101basictunningonOracle9i.pdf

Juan Carlos Reyes Pacheco
OCP



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Received on Thu Feb 26 2004 - 06:48:11 CST

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