Oracle-L: Re: Re[2]: sequence numbers

From: Mark J. Bobak <mark_at_bobak.net>
Date: Thu, 10 Oct 2002 16:33:50 -0800
Message-ID: <F001.004E6644.20021010163350@fatcity.com>

Hi Dick,

I have to disagree with you here. Particularly in the case where this sequence will see any sort of concurrency, from multiple concurrent sessions accessing it. This is due to the serialization on the SQ enqueue. This will cause far worse scalability issues than any I/O. Not that I/O is insignificant, but in this situation, serialization on the enqueue will be the real showstopper for scalability.

As to losing the cached values, well, so what? If your design is such that it's important to have an unbroken contiguous sequence of numbers with no gaps, then I would argue that is a serious design flaw. Also, if that's your requirement, then a sequence is not appropriate, since it can and will end up causing gaps, the first time you roll back a transaction.

Finally, as to sequences losing cached values, unless your instance crashes or does a shutdown abort, Oracle should not loose any sequence values.

-Mark

On Thu, 2002-10-10 at 18:18, dgoulet_at_vicr.com wrote:
> Actually there is no IO penalty since Oracle has to treat the sequence just like
> any table with the old LRU algorithm. I have several sequences with a cache of
> 0 and they perform as well as those with a cache value. The big difference is
> when you shut down the database and all of those cached values end up in the
> trash.
>
> Dick Goulet
>
> ____________________Reply Separator____________________
> Author: "Yechiel Adar" <adar76_at_inter.net.il>
> Date: 10/10/2002 1:38 PM
>
> I think that you will have an update to the sequence number EVERY time instead
> of every 20 times. That's mean I/o for every nextval.
>
> Yechiel Adar
> Mehish
> ----- Original Message -----
> From: Tim Gorman
> To: Multiple recipients of list ORACLE-L
> Sent: Thursday, October 10, 2002 7:43 PM
> Subject: Re: sequence numbers
>
>
> CACHE 20 is the default, so if you remove the clause, it will have absolutely
> no impact on performance or anything else...
>
> ...of course, I get the feeling that that wasn't the gist of your question,
> was it?
> ----- Original Message -----
> From: April Wells
> To: Multiple recipients of list ORACLE-L
> Sent: Wednesday, October 09, 2002 8:54 AM
> Subject: sequence numbers
>
>
> I have been given create scripts for sequences to be used in tables that
> will be loaded via bulk loads. How huge is the potential performance hit if I
> take out the cache 20?
>
> April Wells
> Oracle DBA
> There is neither good nor bad, but thinking makes it so. -Shakespeare
>
>
> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
> <HTML><HEAD>
> <META content="text/html; charset=iso-8859-1" http-equiv=Content-Type>
> <META content="MSHTML 5.00.2314.1000" name=GENERATOR>
> <STYLE></STYLE>
> </HEAD>
> <BODY bgColor=#ffffff
> style="FONT: 10pt Times New Roman; MARGIN-LEFT: 2px; MARGIN-TOP: 2px">
> <DIV><FONT face=Arial size=3>I think that you will have an update to the
> sequence number EVERY time instead of every 20 times. That's mean I/o for every
> nextval.</FONT></DIV>
> <DIV> </DIV>
> <DIV>Yechiel Adar<BR>Mehish</DIV>
> <BLOCKQUOTE dir=ltr
> style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px;
> PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
> <DIV
> style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
> <A href="mailto:Tim_at_SageLogix.com" title=Tim_at_SageLogix.com>Tim Gorman</A>
> </DIV>
> <DIV style="FONT: 10pt arial"><B>To:</B> <A href="mailto:ORACLE-L_at_fatcity.com"
>
> title=ORACLE-L_at_fatcity.com>Multiple recipients of list ORACLE-L</A> </DIV>
> <DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, October 10, 2002 7:43
> PM</DIV>
> <DIV style="FONT: 10pt arial"><B>Subject:</B> Re: sequence numbers</DIV>
> <DIV><BR></DIV>
> <DIV><FONT face=Arial>CACHE 20 is the default, so if you remove the clause, it
>
> will have absolutely no impact on performance or anything else...</FONT></DIV>
> <DIV><FONT face=Arial></FONT> </DIV>
> <DIV><FONT face=Arial>...of course, I get the feeling that that wasn't the
> gist of your question, was it?</FONT></DIV>
> <BLOCKQUOTE dir=ltr
> style="BORDER-LEFT: #000000 2px solid; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px;
> PADDING-LEFT: 5px; PADDING-RIGHT: 0px">
> <DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
> <DIV
> style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color:
> black"><B>From:</B>
> <A href="mailto:awells_at_csedge.com" title=awells_at_csedge.com>April Wells</A>
> </DIV>
> <DIV style="FONT: 10pt arial"><B>To:</B> <A
> href="mailto:ORACLE-L_at_fatcity.com" title=ORACLE-L_at_fatcity.com>Multiple
> recipients of list ORACLE-L</A> </DIV>
> <DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, October 09, 2002 8:54
> AM</DIV>
> <DIV style="FONT: 10pt arial"><B>Subject:</B> sequence numbers</DIV>
> <DIV><BR></DIV>
> <DIV><SPAN class=841194713-09102002>I have been given create scripts for
> sequences to be used in tables that will be loaded via bulk loads.  How
>
> huge is the potential performance hit if I take out the cache
> 20?</SPAN></DIV>
> <DIV> </DIV>
> <P><FONT face="Courier New">April Wells</FONT> <BR><FONT
> face="Courier New">Oracle DBA </FONT><BR><SPAN
> class=841194713-09102002><FONT face="Courier New">T<SPAN
> class=841194713-09102002>here is neither good nor bad, but thinking makes it
>
> so.
> -Shakespeare</SPAN></FONT></SPAN></P></BLOCKQUOTE></BLOCKQUOTE></BODY></HTML>
>

-- 
--
Mark J. Bobak
Oracle DBA
mark_at_bobak.net
"It is not enough to have a good mind.  The main thing is to use it
well."
 						-- Rene Descartes
-- 
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Author: Mark J. Bobak
  INET: mark_at_bobak.net

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Received on Thu Oct 10 2002 - 19:33:50 CDT