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What happens if an index does not fit into RAM in mongodb?

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What happens if an index does not fit into RAM in mongodb?
posted Jan 20, 2017 by Dhaval Vaghela

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1 Answer

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If the indexes do not fit into RAM, MongoDB reads data from disk which is relatively very much slower than reading from RAM.

answer Jan 20, 2017 by Manikandan J
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As far as I know , to check for the amount of installed RAM on my centos server I checked it as:

#more /proc/meminfo

Can you please let me know how can I check for the instantaneous occupied amount of my RAM the similar way the task manager shows it on my Win server?

+3 votes

I have few questions about Cache Memory

1) My understanding of cache memory is, there are 3 type of cache memory,
1. Within RAM
2. Within CPU (L1,L2,L3)
3. Separate Hardware which is costlier than all others.

Please correct if I am wrong,

2) Who stores the data into cache? I mean, can we write a program which should use only cache memory? If yes then how to do it? if no then who manages that?
For example,
Cache memory within RAM, is it managed by Kernel?(Memory Management Unit)
Cache memory within CPU, is it managed by CPU itself?

3) Why cache memory is faster than RAM?

0 votes

According to CDD document, it is stated below"Device implementations MUST have at least 340MB of memory available to the kernel and userspace. The 340MB MUST be in addition to any memory dedicated to hardware components such as radio, video, and so on that is not under the kernel's control."

MY understanding:
340 MB is required for both user and kernel space. 340 MB is for hardware components , So, in total minimum 680 MB (Please correct me if my understanding is wrong ?)

But, if i look at mobiles that are available in the market, they are not compliance with the requirement. (HTC ONE V , has 512 MB of RAM, but still runs android 4.0.3 , in which the requirement is 680MB.)

Considering above, how the OEM vendor passes compatibility test?

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