What is a SGA Granule?

Memory allocation in SGA is done in small chunks. The unit is called as granule. The number and size of granules are determined at startup.

The Granule size will depend on the SGA_MAX_SIZE value and hardware platform.

If SGA_MAX_SIZE <= 128 mb, granule size will be 4 mb
If SGA_MAX_SIZE > 128 mb, granule size will be 16 mb

Following query can be used to check the granule size of SGA components

SELECT COMPONENT, GRANULE_SIZE/(1024*1024) “GRANULE_SIZE(Mb)” FROM V$SGA_DYNAMIC_COMPONENTS
/


In some exceptional cases, we will have to change the granule size > 16

For example: We have 128G of physical memory & we want to allocate 100G to SGA_MAX_SIZE, then granule size of 16Mb may not be sufficient.

Hidden parameter “_ksmg_granule_size” can be used to change the granule size. This parameter should only be changed after consulting with Oracle support.

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