Re: using temp tables for staging databases?

From: Tim Gorman <tim_at_sagelogix.com>
Date: Mon, 20 Oct 2003 21:09:26 -0800
Message-ID: <F001.005D3C4D.20031020210926@fatcity.com>

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: http://www.orafaq.net
-- 
Author: Tim Gorman
  INET: tim_at_sagelogix.com

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Received on Tue Oct 21 2003 - 00:09:26 CDT