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This article shows you how to analyze Extent in ASM. The content is concise and easy to understand. It will definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

The unit in which space is allocated in ASM is that AU,Extent contains one or more AU.

Before 11g, 1 Extent corresponds to 1 AU. Starting from 11.1.0, Oracle introduced Variable Sized Extents,ASM to automatically determine the size of Extent according to the size of the file. The specific algorithm is as follows:

1. If the AU is less than 4MB:

The first 20000 Extent (0-19999J 20GB), Extent size = 1*AU

The next 20000 Extent (20000-39999) 20GB Murray 40GB, Extent size = 4*AU

For the next Extent (40000 minutes and above 40GB), Extent size = 16*AU

2. If AU is greater than or equal to 4MB, and RDBMS compatible is 11.2.0.4 or above, ASM will calculate the size of Extent according to Application Block Size.

By introducing Variable Sized Extents, you can reduce the memory of SGA and improve performance.

Let's take a look at the Extent allocation in the real world:

1. Small data files

FILE_NAME SIZE (MB)

-

+ DATA01/HERA/DATAFILE/system.258.940635333 790

The data file has only 790MB. According to the above allocation rules, the Extent=1*AU of the data file

09:31:28 nolog > select distinct size_kffxp from x$kffxp where number_kffxp = 258

SIZE_KFFXP

-

one

The above information shows that there is really only one case like 1AU.

2. Larger data files

FILE_NAME SIZE (MB)

-

+ DATA01/HERA/DATAFILE/test.363.941274405 24576

The data file is 24g. According to the above allocation rules, the Extent of the data file has two situations: 1AU and 4AU.

09:03:51 nolog > select distinct size_kffxp from x$kffxp where number_kffxp = 363

SIZE_KFFXP

-

one

four

The above is how to analyze Extent in ASM. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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