Re: Are there performancebenefits to reorganizing database-using export/import?
From: Robert Klemme <shortcutter_at_googlemail.com>
Date: Tue, 11 Nov 2008 23:09:13 +0100
Message-ID: <6nue4aFvmu0U2@mid.individual.net>
>> On Nov 10, 3:52 pm, zigzag..._at_yahoo.com wrote:
>> While you are at it, you might consider key compression of
>> concatenated indexes.
>> This can reduce the space used by indexes, but you might need to re-
>> order the columns in the index in order to gain the space reduction
>> that you're after.
Date: Tue, 11 Nov 2008 23:09:13 +0100
Message-ID: <6nue4aFvmu0U2@mid.individual.net>
On 11.11.2008 16:59, Shakespeare wrote:
> bdbafh schreef:
>> On Nov 10, 3:52 pm, zigzag..._at_yahoo.com wrote:
>>> I am using Oracle 9.2.0.5 on HP UNIX 11i. Since it is a production > ------------------------------------------
>> While you are at it, you might consider key compression of
>> concatenated indexes.
>> This can reduce the space used by indexes, but you might need to re-
>> order the columns in the index in order to gain the space reduction
>> that you're after.
> > I would definitely NOT advise to do so. Column order is rather important > in indexes!
Especially since for fast lookups you want most selective (high cardinality) columns first but for good compression you want low cardinality columns first. And then there are other considerations (i.e. column order which helps most queries) as well...
Kind regards
robert Received on Tue Nov 11 2008 - 16:09:13 CST