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	<title>Dion Cho - Oracle Performance Storyteller</title>
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	<description>We are natural born scientists</description>
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		<title>Dion Cho - Oracle Performance Storyteller</title>
		<link>http://dioncho.wordpress.com</link>
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		<item>
		<title>Interesting case of the restriction of global hints</title>
		<link>http://dioncho.wordpress.com/2010/12/17/interesting-case-of-the-restriction-of-global-hints/</link>
		<comments>http://dioncho.wordpress.com/2010/12/17/interesting-case-of-the-restriction-of-global-hints/#comments</comments>
		<pubDate>Fri, 17 Dec 2010 05:21:59 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Uncategorized]]></category>
		<category><![CDATA[dbms_xplan]]></category>
		<category><![CDATA[global hint]]></category>
		<category><![CDATA[qb_name]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1096</guid>
		<description><![CDATA[One of my colleagues sent following test case, of which he couldn&#8217;t control the join order with hints. 1. Create objects &#8211; table t1, t2 and t3 SQL&#62; create table t1(c1 number, c2 number); Table created. SQL&#62; create table t2(c1 number, c2 number); Table created. SQL&#62; create table t3(c1 number, c2 number); Table created. 2. [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1096&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/12/17/interesting-case-of-the-restriction-of-global-hints/feed/</wfw:commentRss>
		<slash:comments>1</slash:comments>
	
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		<title>Interpreting Parallel MERGE Statement</title>
		<link>http://dioncho.wordpress.com/2010/12/10/interpreting-parallel-merge-statement/</link>
		<comments>http://dioncho.wordpress.com/2010/12/10/interpreting-parallel-merge-statement/#comments</comments>
		<pubDate>Fri, 10 Dec 2010 04:19:43 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Parallel Execution]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1081</guid>
		<description><![CDATA[This post is inspired by one of my colleagues, who had small difficulty while interpreting parallel MERGE execution plan. This is the step-by-step explanation I gave him. 1. Create tables. SQL&#62; create table t1 2 as 3 select 4 level as c1, 5 level as c2, 6 rpad('x',100) as c3 7 from 8 dual 9 [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1081&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/12/10/interpreting-parallel-merge-statement/feed/</wfw:commentRss>
		<slash:comments>1</slash:comments>
	
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		<item>
		<title>Making self deadlock on the library cache pin</title>
		<link>http://dioncho.wordpress.com/2010/09/16/making-self-deadlock-on-the-library-cache-pin/</link>
		<comments>http://dioncho.wordpress.com/2010/09/16/making-self-deadlock-on-the-library-cache-pin/#comments</comments>
		<pubDate>Thu, 16 Sep 2010 02:06:26 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Troubleshooting]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1071</guid>
		<description><![CDATA[It&#8217;s very easy to make your session deadlocked on the library cache pin. Let me prove it. Step 1. Make a dummy procedure called TEST_PROC1. TPACK@ukja1120&#62; select * from v$version where rownum = 1; BANNER ----------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.1.0 - Production create or replace procedure test_proc1 is begin null; end; / [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1071&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/09/16/making-self-deadlock-on-the-library-cache-pin/feed/</wfw:commentRss>
		<slash:comments>4</slash:comments>
	
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		<title>Batching NLJ optimization and ordering</title>
		<link>http://dioncho.wordpress.com/2010/08/16/batching-nlj-optimization-and-ordering/</link>
		<comments>http://dioncho.wordpress.com/2010/08/16/batching-nlj-optimization-and-ordering/#comments</comments>
		<pubDate>Mon, 16 Aug 2010 06:33:04 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Troubleshooting]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1049</guid>
		<description><![CDATA[You might be aware of the batching nested loops join(batching NLJ) optimization introduced at Oracle 11g. For who are not aware of this new feature, let me show you two different execution plans(Oracle 10g vs. 11g) of the same SQL. -- Oracle 10g ------------------------------------------------ &#124; Id &#124; Operation &#124; Name &#124; ------------------------------------------------ &#124; 0 &#124; [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1049&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/08/16/batching-nlj-optimization-and-ordering/feed/</wfw:commentRss>
		<slash:comments>5</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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		<item>
		<title>_gby_hash_aggregation_enabled bug</title>
		<link>http://dioncho.wordpress.com/2010/07/06/_gby_hash_aggregation_enabled-bug/</link>
		<comments>http://dioncho.wordpress.com/2010/07/06/_gby_hash_aggregation_enabled-bug/#comments</comments>
		<pubDate>Tue, 06 Jul 2010 05:52:49 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Troubleshooting]]></category>
		<category><![CDATA[HASH GROUP BY]]></category>
		<category><![CDATA[SORT GROUP BY]]></category>
		<category><![CDATA[_gby_hash_aggregation_enabled]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1035</guid>
		<description><![CDATA[One of the customers complained that Oracle refuses to use the HASH GROUP BY operation under any circumstances. It&#8217;s 10gR2(10.2.0.1) database. TPACK@ukja1021&#62; select * from v$version where rownum = 1; BANNER ---------------------------------------------------------------- Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Prod See that Oracle simply refuses to use HASH GROUP BY operation even with the [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1035&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/07/06/_gby_hash_aggregation_enabled-bug/feed/</wfw:commentRss>
		<slash:comments>2</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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	</item>
		<item>
		<title>Rapid PGA size increase</title>
		<link>http://dioncho.wordpress.com/2010/06/14/rapid-pga-size-increase/</link>
		<comments>http://dioncho.wordpress.com/2010/06/14/rapid-pga-size-increase/#comments</comments>
		<pubDate>Mon, 14 Jun 2010 02:10:45 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Troubleshooting]]></category>
		<category><![CDATA[10261]]></category>
		<category><![CDATA[ORA-4030]]></category>
		<category><![CDATA[ORA-600]]></category>
		<category><![CDATA[PGA]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1020</guid>
		<description><![CDATA[A couple of days ago, one of our customers experienced a rapid PGA increase and the system got rebounced by PMON. We suggested dumping the PGA heap while the problem reoccurs. But the problem is that the PGA increase is too rapid(upto 3.6G in less than 2 min), so it is a bit hard to [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1020&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/06/14/rapid-pga-size-increase/feed/</wfw:commentRss>
		<slash:comments>8</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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		<item>
		<title>Interesting combination of RAC and serial direct path read</title>
		<link>http://dioncho.wordpress.com/2010/06/09/interesting-combination-of-rac-and-serial-direct-path-read/</link>
		<comments>http://dioncho.wordpress.com/2010/06/09/interesting-combination-of-rac-and-serial-direct-path-read/#comments</comments>
		<pubDate>Wed, 09 Jun 2010 04:31:36 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[I/O]]></category>
		<category><![CDATA[serial direct path read]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1013</guid>
		<description><![CDATA[For who are not aware, Oracle 11g has introduced a serial direct path read which enables the efficient direct path read for the serial table scan. Disabling Direct path read for the serial full table scan-11g A couple of days ago, I was reported a weird performance bias between 2 nodes in 11g RAC. The [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1013&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/06/09/interesting-combination-of-rac-and-serial-direct-path-read/feed/</wfw:commentRss>
		<slash:comments>7</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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		<item>
		<title>Underperformance of V$SQL_OPTIMIZER_ENV</title>
		<link>http://dioncho.wordpress.com/2010/05/20/underperformance-of-vsql_optimizer_env/</link>
		<comments>http://dioncho.wordpress.com/2010/05/20/underperformance-of-vsql_optimizer_env/#comments</comments>
		<pubDate>Thu, 20 May 2010 02:21:55 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Misc.]]></category>
		<category><![CDATA[V$SQL_OPTIMIZER_ENV]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=1003</guid>
		<description><![CDATA[A couple of days ago, I was trying to search the non-default optimizer environments(aka. parameters) of a specific SQL query which has multiple child cursors. But it soon turned out that it&#8217;s almost impossible to search this simple view just because of the underperformance. Followings are what I mean. 1. Create simple objects and gather [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=1003&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2010/05/20/underperformance-of-vsql_optimizer_env/feed/</wfw:commentRss>
		<slash:comments>8</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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		<item>
		<title>Trivial Research on the Cardinality Feedback on 11gR2</title>
		<link>http://dioncho.wordpress.com/2009/12/17/trivial-research-on-the-cardinality-feedback-on-11gr2/</link>
		<comments>http://dioncho.wordpress.com/2009/12/17/trivial-research-on-the-cardinality-feedback-on-11gr2/#comments</comments>
		<pubDate>Thu, 17 Dec 2009 07:45:46 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Optimizer]]></category>
		<category><![CDATA[Cardinality feedback]]></category>
		<category><![CDATA[OPT_ESTIMATE]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=981</guid>
		<description><![CDATA[These are findings and dicussions on the undocumented cardinality feedback implementation on Oracle 11gR2. Adaptive Optimisation ? Hidden and Undocumented &#8220;Cardinality Feedback&#8221; This is a very fantastic but embarassing feature, so I decided to reproduce it myself and have some research on it. I focused on the following questions. Can I reproduce it? How does [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=981&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2009/12/17/trivial-research-on-the-cardinality-feedback-on-11gr2/feed/</wfw:commentRss>
		<slash:comments>9</slash:comments>
	
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			<media:title type="html">dioncho</media:title>
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		<item>
		<title>Logging in PL/SQL</title>
		<link>http://dioncho.wordpress.com/2009/11/10/logging-in-plsql/</link>
		<comments>http://dioncho.wordpress.com/2009/11/10/logging-in-plsql/#comments</comments>
		<pubDate>Tue, 10 Nov 2009 08:40:42 +0000</pubDate>
		<dc:creator>Dion Cho</dc:creator>
				<category><![CDATA[Programming]]></category>
		<category><![CDATA[PL/SQL]]></category>

		<guid isPermaLink="false">http://dioncho.wordpress.com/?p=972</guid>
		<description><![CDATA[What is the best debugging tool ever invented in the history of the programming langauge? We have a choice of many powerful and cutting-edge tools these days, but still, the most powerful and handy debugging tool is logging which is written by developers themselves. But unfortunately, PL/SQL has a weaking functionality on the logging and [...]<img alt="" border="0" src="http://stats.wordpress.com/b.gif?host=dioncho.wordpress.com&amp;blog=3612783&amp;post=972&amp;subd=dioncho&amp;ref=&amp;feed=1" width="1" height="1" />]]></description>
		<wfw:commentRss>http://dioncho.wordpress.com/2009/11/10/logging-in-plsql/feed/</wfw:commentRss>
		<slash:comments>3</slash:comments>
	
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