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Home -> Community -> Mailing Lists -> Oracle-L -> Re: using temp tables for staging databases?
For PCTFREE, setting it to less than the default of 10 is an option for
tables that are INSERT-only where someone wants to "pack" rows into the
blocks. The attendent risks are that UPDATEs causing row expansion may be
forced to migrate to another block, thus hurting subsequent query
performance. Setting PCTFREE greater than the default of 10 is a good idea
if you have experienced row-migration in the past (or expect to experience
it) and you want to leave more free space in each block to accommodate row
expansion from UPDATE statements.
For PCTUSED, I just can't imagine any practical real-world reasons to change it from the default of 40. I'm sure someone else can...
on 10/21/03 2:19 AM, Mark Leith at 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
>> at 99 and 1 to pack in the blocks and we use very small extent sizes. then
>> 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
>> that a 'create table as' is MUCH faster than inserting into global
>> 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
>> 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
>>> ever become "large"? >>> >>> As with OraApps "open interface" tables, it is when a large volume of
>>> 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
>>> on the interface/temporary tables to run slowly. The only way to bring
>>> 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
>>>> by >>>> using smaller temporary tables(not global temp tables) they can increase
>>>> speed of the data loads. >>>> >>>> Not worried about latch contention because its just for bulk loads. I
>>>> 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 >>> >>> Fat City Network Services -- 858-538-5051 http://www.fatcity.com >>> San Diego, California -- Mailing list and web hosting services >>> --------------------------------------------------------------------- >>> To REMOVE yourself from this mailing list, send an E-Mail message >>> to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in >>> the message BODY, include a line containing: UNSUB ORACLE-L >>> (or the name of mailing list you want to be removed from). You may >>> also send the HELP command for other information (like subscribing). >>>
-- Please see the official ORACLE-L FAQ: http://www.orafaq.net -- Author: Tim Gorman INET: tim_at_sagelogix.com Fat City Network Services -- 858-538-5051 http://www.fatcity.com San Diego, California -- Mailing list and web hosting services --------------------------------------------------------------------- To REMOVE yourself from this mailing list, send an E-Mail message to: ListGuru_at_fatcity.com (note EXACT spelling of 'ListGuru') and in the message BODY, include a line containing: UNSUB ORACLE-L (or the name of mailing list you want to be removed from). You may also send the HELP command for other information (like subscribing).Received on Tue Oct 21 2003 - 08:24:25 CDT
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