Hi, Mark.
I'm not Tim, but I did encounter such a situation.
This was not a temp table, but a permanent one.
We have a db with a very strange block size of 4608
(actually Tim is painfully aware of this one). We have
a very large table in this database. It was expanding
at about 200 megs per week -- way out of control for a
relataively small database.
The database was not reusing blocks. Oracle
recommends that (100% - (pctfree+pcused)) be greater
than the maximum sie of a row. So we did an exact
calculation of the blocksize less %free+%used
1% of a block is 46.08
80% of a block is 3686.4
4608 - (46.08 + 3686.4) = 875.52
our largest row length is 860
So we set pctfree at 1% and pctused at 80%
One of the reasons we can get by with this is because
the vendor designed the database with all char (not
varchar2), so we pretty much know exactly what each
row is going to consume. (It's a Cobol app)
After this change, the database stopped it's wild
expansion.
Not a normal situation, but then nothing here is
normal. (Kids -- don't try this at home!)
Barb
- Mark Leith <mark_at_cool-tools.co.uk> wrote:
> Tim,
>
> Can you sum up a few situations when the need *has*
> arisen to change these
> values?
>
> Cheers
>
> Mark
>
>
>
> -----Original Message-----
> Tim Gorman
> Sent: 21 October 2003 06:09
> To: Multiple recipients of list ORACLE-L
>
>
> Unless you typo'd, there are some serious problems
> here...
>
> Setting PCTFREE to 99 is not likely to "pack in the
> blocks". Rather the
> opposite; you are instead leaving blocks 99% empty.
> Quite a bit of wasted
> I/O in performing a FULL table scan here... :-)
>
> Anyway, it is not a good idea to have PCTFREE and
> PCTUSED sum to a value
> greater than 70 or 80 or so, just as a rule of
> thumb. Having them sum to a
> value near 100 ensures that each insert, delete, or
> even update will
> potentially cause the block to be removed or
> reinserted to one of the
> segment's free list. Think about it: the width of
> a single row crossing
> the boundary from "off the free list" to "on the
> free list". Better to
> leave a bit of a "no man's land" between the two
> values. The default
> settings of PCTFREE=10 and PCTUSED=40 are one of the
> few default settings
> that need little manipulation for most situations.
>
>
>
> on 10/20/03 7:34 AM, rgaffuri_at_cox.net at
> rgaffuri_at_cox.net wrote:
>
> > we drop and recreate the temp tables every night.
> We also use PCTFREE
> PCTUSED
> > at 99 and 1 to pack in the blocks and we use very
> small extent sizes. then
> we
> > analyze with an estimate size of 20 percent which
> is quite fast.
> >
> > All of them are used for full table scans and do
> not have indexes. Ive
> found
> > that a 'create table as' is MUCH faster than
> inserting into global
> temporary
> > tables when you do not have to worry about latch
> contention(ie 1-3 users
> > logged in at a time).
> >
> > anyone else notice this? Seems to go against
> conventional wisdom which
> says
> > never use them. So I want to make sure Im not
> missing something.
> >>
> >> From: Tim Gorman <tim_at_sagelogix.com>
> >> Date: 2003/10/20 Mon AM 10:19:33 EDT
> >> To: Multiple recipients of list ORACLE-L
> <ORACLE-L_at_fatcity.com>
> >> Subject: Re: using temp tables for staging
> databases?
> >>
> >> All the time. Oracle Apps's "open interfaces"
> are built this way, for
> >> example.
> >>
> >> However, "the guys here" covered their bases by
> specifying "smaller
> >> temporary tables", as if they could prevent them
> from becoming large. I
> >> suppose they might feel that they indemnify
> themselves if the tables
> should
> >> ever become "large"?
> >>
> >> As with OraApps "open interface" tables, it is
> when a large volume of
> data
> >> is pushed through that the trouble starts. The
> "high-water marks" on all
> >> the tables are pushed to a high level, thereafter
> causing full table
> scans
> >> on the interface/temporary tables to run slowly.
> The only way to bring
> the
> >> HWM back down is quiesce the interface/app and
> then truncate the tables.
> >>
> >>
> >>
> >> on 10/20/03 6:39 AM, rgaffuri_at_cox.net at
> rgaffuri_at_cox.net wrote:
> >>
> >>> This is for non-transactional data load
> instances. The guys here sware
> that
> >>> by
> >>> using smaller temporary tables(not global temp
> tables) they can increase
> the
> >>> speed of the data loads.
> >>>
> >>> Not worried about latch contention because its
> just for bulk loads. I
> know
> >>> this bad in transactional instances. Has anyone
> used these in
> >>> non-transactional data load instances?
> >>
> >> --
> >> Please see the official ORACLE-L FAQ:
> http://www.orafaq.net
> >> --
> >> Author: Tim Gorman
> >> INET: tim_at_sagelogix.com
> >>
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> --
> Please see the official ORACLE-L FAQ:
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> --
> Author: Tim Gorman
> INET: tim_at_sagelogix.com
>
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Received on Tue Oct 21 2003 - 10:19:25 CDT
