Re: the 20% rule
Date: Sat, 26 Jul 2008 15:59:48 +1000
David BL <davidbl_at_iinet.net.au> writes:
> On Jul 24, 10:01 pm, aark..._at_gmail.com wrote:
>> The fastest way to retrieve rows from a table is to access the row
>> with exact row id. An
>> index is the second fastest way
> I'm no expert in oracle, but my understanding is that it provides so
> called heap organised tables or else index organised tables. The
> above comment would seem to apply to the former not the latter.
Oracle provides a wealth of options with respect to table organisation, indexes etc. Rowid is very fast because it identifies the exact row in the table to retrieve. The problem is that you rarely know the rowid without first having selected the row - its not like using an index where you can say "give me all records where the field x = y". However, if you do know the rowid of the row you are interested in, it is very fast because you access it directly from the table and not by first reading the index to get the table location and then reading it from the table. At least, thats sort of my understanding in a siplistic way.
-- tcross (at) rapttech dot com dot auReceived on Sat Jul 26 2008 - 07:59:48 CEST