Comments on: DUAL behavior change http://awads.net/wp/2005/11/09/dual-behavior-change/ News, views, tips and tricks on Oracle and other fun stuff Fri, 21 Nov 2008 03:40:23 +0000 http://wordpress.org/?v=2.6.3 By: Carl r. http://awads.net/wp/2005/11/09/dual-behavior-change/#comment-323 Carl r. Tue, 22 Nov 2005 11:41:19 +0000 http://awads.net/wp/?p=161#comment-323 <p>hi - great news; that's what i like in the 10g release - there are also a lot of small changes with big effect.</p> <p>Carl</p> hi - great news;
that’s what i like in the 10g release - there are also a lot of small changes with big effect.

Carl

]]> By: UM http://awads.net/wp/2005/11/09/dual-behavior-change/#comment-282 UM Thu, 10 Nov 2005 19:31:08 +0000 http://awads.net/wp/?p=161#comment-282 <p>Keep in mind that we should not refer to 'dummy' column of Dual table. If we do, plan will revert back to 5 c.gets.</p> <p>Usually, we don't need to refer dummy column, but I had seen some code like that!</p> Keep in mind that we should not refer to ‘dummy’ column of Dual table. If we do, plan will revert back to 5 c.gets.

Usually, we don’t need to refer dummy column, but I had seen some code like that!

]]> By: yas http://awads.net/wp/2005/11/09/dual-behavior-change/#comment-281 yas Thu, 10 Nov 2005 11:52:41 +0000 http://awads.net/wp/?p=161#comment-281 <p><i>Since I only need the SYSDATE, which is not stored in the DUAL table, why scan (full or not) the DUAL (or any) table?</i> Definitely. We had this query which is executed more than 2 million times in every half hour. SELECT SYS_CONTEXT(:B2,:B1) FROM SYS.DUAL Creating and index on dual made it 1/3. Seems it will be better when we upgrade to 10G.</p> Since I only need the SYSDATE, which is not stored in the DUAL table, why scan (full or not) the DUAL (or any) table?
Definitely. We had this query which is executed more than 2 million times in every half hour.
SELECT SYS_CONTEXT(:B2,:B1) FROM SYS.DUAL
Creating and index on dual made it 1/3. Seems it will be better when we upgrade to 10G.

]]> By: Eddie Awad http://awads.net/wp/2005/11/09/dual-behavior-change/#comment-280 Eddie Awad Wed, 09 Nov 2005 23:54:14 +0000 http://awads.net/wp/?p=161#comment-280 <p>Hi Rob, </p> <p>I guess it does not matter much in the case of DUAL. However, "0 consistent gets" is better than "3 consistent gets" because, quoting <a href="http://asktom.oracle.com/pls/ask/f?p=4950:8:::::F4950_P8_DISPLAYID:6643159615303#6653929680584" rel="nofollow">AskTom</a>: "Each consistent get is a latch, latches = contention".</p> <p>Since I only need the SYSDATE, which is not stored in the DUAL table, why scan (full or not) the DUAL (or any) table?</p> Hi Rob,

I guess it does not matter much in the case of DUAL. However, “0 consistent gets” is better than “3 consistent gets” because, quoting AskTom: “Each consistent get is a latch, latches = contention”.

Since I only need the SYSDATE, which is not stored in the DUAL table, why scan (full or not) the DUAL (or any) table?

]]> By: Robert Vollman http://awads.net/wp/2005/11/09/dual-behavior-change/#comment-279 Robert Vollman Wed, 09 Nov 2005 23:17:35 +0000 http://awads.net/wp/?p=161#comment-279 <p>Eddie, I am missing something. DUAL has just one row, why does it matter if Oracle does a full tablescan of a single-row table (that is very likely in the cache anyway)?</p> Eddie, I am missing something. DUAL has just one row, why does it matter if Oracle does a full tablescan of a single-row table (that is very likely in the cache anyway)?

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