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3 Replies Latest reply: Apr 18, 2013 11:45 PM by Hemant K Chitale RSS

Direct path read vs Full table scan

706543 Newbie
Currently Being Moderated
Hi,

I am bit confused the term Direct path read with Full table scan.

Does direct path read refers to Full table scan operation?
  • 1. Re: Direct path read vs Full table scan
    Marc Fielding Journeyer
    Currently Being Moderated
    Hello user8018298,

    This is a great question but a bit complex to answer in this type of forum. The quick answer: a full table scan is sometimes a direct path read. It depends on your database version (adaptive direct path reads appeared in 11g), table size, parallelism, and other factors. If you're interested in the topic. Frits Hoogland has done quite a bit of work on this topic, and has an excellent presentation on it: http://fritshoogland.files.wordpress.com/2012/06/about-multiblock-reads-v2.pdf

    Marc
  • 2. Re: Direct path read vs Full table scan
    UweHesse Expert
    Currently Being Moderated
    A Direct Read can happen on behalf of a Full Table Scan or an Index Fast Full Scan
    Not every Full Table Scan respectively Index Fast Full Scan will trigger a Direct Read, though.

    A Direct Read is a prerequisite to get a Smart Scan

    Kind regards
    Uwe Hesse

    "Don't believe it, test it!"
    http://uhesse.com
  • 3. Re: Direct path read vs Full table scan
    Hemant K Chitale Oracle ACE
    Currently Being Moderated
    A direct path read bypasses the buffer cache --- data is read from the database directly to the server process'es PGA. A Full Table Scan may be a direct path read if it is not small. Reads using Parallel Query are direct path reads.


    Hemant K Chitale

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