Hash Based Column Sampling In 11g As Compared To RowBased....

From: Aman Sharma <amansharma1981_at_gmail.com>
Date: Fri, 19 Dec 2008 03:49:22 -0800 (PST)
Message-ID: <99537927-999a-431f-9712-21e89e415f63@z6g2000pre.googlegroups.com>


Hi,
In 11g (11106), here is what is mentioned about the stats gathering, http://download.oracle.com/docs/cd/B28359_01/server.111/b28274/stats.htm#PFGRF30102 In the 11g NF guide from OU, it is mentioned that prior to 11g , the column sampling was done with the help of "Row Based Sampling". In 11g, if one uses, ESTIMATE_PERCENT=>AUTO_SAMPLE_SIZE than the sampling technique is Hash Based. This is by default there from 11g onwards. Here are my questions,

1)What is the older Row Based Sampling and how it works?
2) What is the new Hash Based Sampling and how it works?
3) What's the benefit of the new technique?
Thanks in advance.
Aman.... Received on Fri Dec 19 2008 - 05:49:22 CST

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