Hacker News new | ask | show | jobs
by tremon 133 days ago
I'm also in the GP's camp; RAM is for volatile data, disk is for data persistence. The first "why would you do that" that needs to be addressed is why volatile data should be written to disk. And "it's just a few % of your disk" is not a sufficient answer to that question.
2 comments
112233 133 days ago
> RAM is for volatile data, disk is for data persistence.

Genuinely curious where this idea has come from. Is it something being taught currently?

link
tremon 133 days ago
No, not currently -- since the start of computers. This is quite literally part of Computing 101; see https://web.stanford.edu/class/cs101/lecture02.html#/9 , slides 10-12.

You can ask your favourite search engine or language fabricator about the differences between RAM and disk storage, they will all tell you the same thing. Frankly, it's kind of astonishing that this needs to be explained on a site like HN.

link
112233 133 days ago
I have no idea where on those slides it says non-volatile storage should not be used for non-permanent, temporary data.

It does note main differences (speed, latency, permanence). How does that limit what data disk can be used for?

What would one use optane DIMMs for?

Also, if my program requires huge working set to process the data, why would I spend the effort and implement my own paging to templrary working files, instead of allocating ridiculous amount of memory and letting OS manage it for me? What is the benefit?

link
ch_123 133 days ago
Because of cost - particularly given the current state of the RAM market. In order to have so much memory that you never hit memory spikes, you will deliberately need to buy RAM to never be used.

Note that simply buying more RAM than what you expect to use is not going to help. Going back to my post from earlier, I had a laptop with 8GB of RAM at a time where I would usually only need about 2-4GB of RAM for even relatively heavy usage. However, every once in a while, I would run something that would spike memory usage and make the system unresponsive. While I have much more than 8GB nowadays, I'm not convinced that it's enough to have completely outrun the risk of this sort of behaviour re-occuring.

link
em-bee 133 days ago
how much swap do you have? i have 16GB now, and 16GB ram. i had a machine before with 48GB ram. obviously having more ram and no swap should perform better than the same amount of memory split into ram and swap.
link