<div style="margin: 12px 0px; font-family: arial; color: #333333; background: #ffffff; border: solid 4px #e5e5e5; width: 100%; clear: left;"><div class="CM_CTB_Content_Wrap" style="margin: 0px; padding: 0px;background-color: #ffffff;"><div style="border-bottom: solid 1px #dcdcdc; white-space: nowrap; margin-bottom: 8px; background-color: #eeeeee ;background-image: url(http://www.clipmarks.com/images/source-bg.gif); background-repeat: repeat-x; height: 24px; line-height: 24px; vertical-align: middle; padding-bottom: 4px; color: #666666; font-size: 10px;" ><a href="http://clipmarks.com/clip-to-blog/" title="see clips that are hot right now"><img src="http://content.clipmarks.com/blog_embed/34c11257-104f-4f24-89c3-28b1c05a62be/2A2B3467-0C81-4E66-B739-0D2DEECDF21F/" alt="" width="19" height="19" border="0" style="vertical-align: middle; margin: 0px 4px; display: inline; border: none; float:none;" /></a>clipped from <a title="http://www.akadia.com/services/ora_interpreting_explain_plan.html" href="http://www.akadia.com/services/ora_interpreting_explain_plan.html" style="font-size: 11px;">www.akadia.com</a></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.akadia.com/services/ora_interpreting_explain_plan.html"><P class="normal">An explain plan is a representation of the access path that is taken when a query is executed within Oracle.</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.akadia.com/services/ora_interpreting_explain_plan.html"><P class="normal">Query processing can be divided into 7 phases:</P></blockquote><div style="height: 2px; font-size: 2px; background: #dcdcdc; border-bottom: solid 1px #f5f5f5; margin: 2px 4px;"></div><blockquote style="text-align: left; padding: 0px 8px; margin: 4px 0px 8px 0px; background: transparent; border: none;" cite="http://www.akadia.com/services/ora_interpreting_explain_plan.html"><TABLE width="100%" cellpadding="0" border="0"><TBODY><TR><TD width="25%" valign="top">[1] Syntactic</TD><TD width="75%" valign="top">Checks the syntax of the query</TD></TR><TR><TD width="25%" valign="top">[2] Semantic</TD><TD width="75%" valign="top">Checks that all objects exist and are accessible</TD></TR><TR><TD width="25%" valign="top">[3] View Merging</TD><TD width="75%" valign="top">Rewrites query as join on base tables as opposed to using views</TD></TR><TR><TD width="25%" valign="top">[4] Statement Transformation</TD><TD width="75%" valign="top">Rewrites query transforming some complex constructs into simpler ones where appropriate (e.g. subquery merging, in/or transformation)</TD></TR><TR><TD width="25%" valign="top">[5] Optimization</TD><TD width="75%" valign="top">Determines the optimal access path for the query to take. With the Rule Based Optimizer (RBO) it uses a set of heuristics to determine access path. With the Cost Based Optimizer (CBO) we use statistics to analyze the relative costs of accessing objects.</TD></TR><TR><TD width="25%" valign="top">[6] QEP Generation</TD><TD width="75%" valign="top">QEP = Query Evaluation Plan</TD></TR><TR><TD width="25%" valign="top">[7] QEP Execution</TD><TD width="75%" valign="top">QEP = Query Evaluation Plan</TD></TR></TBODY></TABLE></blockquote></div><div style="margin: 0px 6px 6px 4px;"><table style="font-size: 11px;border-spacing: 0px;padding: 0px;" cellpadding="0" cellspacing="0" width="100%"><tr><td style="background:transparent;border-width:0px;padding:0px;">&nbsp;</td><td align="right" style="background:transparent;border-width:0px;padding:0px;width:107px" width="107"><a href="http://clipmarks.com/share/2A2B3467-0C81-4E66-B739-0D2DEECDF21F/blog/" title="blog or email this clip"><img src="http://content7.clipmarks.com/images/c2b-foot.png" border="0" alt="blog it" width="107" height="17" style="border-width:0px;padding:0px;margin:0px;" /></a></td></tr></table></div></div>

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