# Disabled chunk caching

**URL:** <https://forum.hdfgroup.org/t/disabled-chunk-caching/3554>\
**Category:** Hdf-forum archives\
**Created:** [September 11, 2015, 4:34pm UTC](https://forum.hdfgroup.org/t/disabled-chunk-caching/3554 "2015-09-11T16:34:54Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Brock\_Hargreaves](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/b/fbc32d/32.png) [@Brock\_Hargreaves](https://forum.hdfgroup.org/u/Brock_Hargreaves)\
**Post date:** [September 11, 2015, 4:34pm UTC](https://forum.hdfgroup.org/t/disabled-chunk-caching/3554/1 "2015-09-11T16:34:54Z")

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Hi forum,

Does anyone know a general reason why disabling chunk caching would improve  
performance? I found this to be the case in my application but can't  
explain why.

In a tutorial from Elena Pourmal,

> **[Chunking\_Tutorial\_EOS13\_2009.pdf](https://support.hdfgroup.org/HDF5/doc/Advanced/Chunking/Chunking_Tutorial_EOS13_2009.pdf)**
>
> 672.02 KB

  
:

"Chunk cache size (rdcc\_nbytes) should be large enough to hold all the  
chunks in a selection • If this is not possible, it may be best to disable  
chunk caching altogether (set rdcc\_nbytes to 0)"

Note that even though it is possible in my application, I still gain  
performance by disabling it.

Cheers,  
Brock

---

<div class="post-metadata">

**Author:** ![epourmal](https://forum.hdfgroup.org/letter_avatar_proxy/v4/letter/e/c67d28/32.png) [@epourmal](https://forum.hdfgroup.org/u/epourmal)\
**Post date:** [September 13, 2015, 4:15am UTC](https://forum.hdfgroup.org/t/disabled-chunk-caching/3554/2 "2015-09-13T04:15:26Z")

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Hi Brock,

Less memory is used when chunk cache is disabled (default setting is 1MB per each opened dataset), but it is hard to say without profiling the application.

Elena

> **···**
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  
> Elena Pourmal The HDF Group [http://hdfgroup.org](http://hdfgroup.org)  
> 1800 So. Oak St., Suite 203, Champaign IL 61820  
> 217.531.6112  
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> On Sep 11, 2015, at 11:34 AM, Brock Hargreaves \<[brock.hargreaves@gmail.com](mailto:brock.hargreaves@gmail.com)\<[mailto:brock.hargreaves@gmail.com](mailto:brock.hargreaves@gmail.com)\>\> wrote:
> 
> Hi forum,
> 
> Does anyone know a general reason why disabling chunk caching would improve performance? I found this to be the case in my application but can't explain why.
> 
> In a tutorial from Elena Pourmal, [https://www.hdfgroup.org/HDF5/doc/Advanced/Chunking/Chunking\_Tutorial\_EOS13\_2009.pdf](https://www.hdfgroup.org/HDF5/doc/Advanced/Chunking/Chunking_Tutorial_EOS13_2009.pdf) :
> 
> "Chunk cache size (rdcc\_nbytes) should be large enough to hold all the chunks in a selection • If this is not possible, it may be best to disable chunk caching altogether (set rdcc\_nbytes to 0)"
> 
> Note that even though it is possible in my application, I still gain performance by disabling it.
> 
> Cheers,  
> Brock  
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