RAM Is the New Disk • Hacker News Board

Re: RAM Is the New Disk

#31

Post by AndyNemmity » Mon, Jul 31, 2017, 4:45 AM UTC

arielweisberg wrote: post #5

... I was the third engineer at VoltDB and spent six years making that bet. It's not a good bet. Maybe there are other factors, but if VoltDB could page out cold data to disk I think it would be at least 2x if not more successful. No one agreed with me so it never happened. I saw so many use cases go out the door because hey you know what? RAM is expensive and it's cheaper to page out cold data. The scale where that…

Have spent 6 years I think working on SAP HANA. The one feature I've always asked for is seamless paging of even warmish data to disk.

In memory is fast and awesome, but it doesn't have to be as mind boggling expensive as it is. Why are we all making the same mistakes?

Re: RAM Is the New Disk

#32

Post by AndyNemmity » Mon, Jul 31, 2017, 4:47 AM UTC

adrianratnapala wrote: post #21

If a terabyte is a lot of data to you -- and it is for many, many things, then this post is right; you should buy as much RAM as you have data, and access it accordingly. The commenters who are saying disk has a different price/performance trade-off that is still valuable are also right, but that applies to large data sets.

I worked on a petabyte in memory hana cluster. It all depends on what you're doing, and how important it is to you.

I don't even know what a large data set is anymore. I think my general definition is one you won't put into memory, whatever your threshold is for that.

Re: RAM Is the New Disk

#33

Post by flukus » Mon, Jul 31, 2017, 4:50 AM UTC

0xbear wrote: post #12

And 99% of developers spend their entire careers without giving as much as a passing thought to cache locality. Quick, how long, in cycles, does it take to retrieve data from RAM? About 200 cycles. 200 cycles is a very long time if you miss cache often. Scattered RAM reads can be _slower_ than sustained linear disk reads (that is, once the disk actually gets around to reading, which takes a while).

90% of developers are working in languages where you can't really do much about cache misses, or doing so will at least involve some very non-idiomatic code. If you can't do much about the problem it's not really helpful to be thinking about it much.

Re: RAM Is the New Disk

#34

Post by everheardofc » Mon, Jul 31, 2017, 4:51 AM UTC

olegkikin wrote: post #2

Are you sure latency stayed around 100ns? http://pics.crucial.com/wcsstore/CrucialSAS/images/campaigns...

There are these things called speed of light and virtual memory. The latency of the physical RAM is completely irrelevant unless its embedded directly on the cpu

Re: RAM Is the New Disk

#35

Post by drudru11 » Mon, Jul 31, 2017, 4:54 AM UTC

This post is 10 late

Re: RAM Is the New Disk

#36

Post by pvg » Mon, Jul 31, 2017, 5:25 AM UTC

zeusk wrote: post #29

vbezhenar wrote: post #24

May be with very high-end servers it is. But generally it's not. I can buy 4TB HDD For $200. I think, I'll have to add 2-3 zeros for 4TB RAM machine, and I'm not even saying only about RAM, I need some server motherboard, some server processor, while I can use 4TB RAM HDD with pretty much any computer. And SSD isn't going to be even with HDD in near future as well for $/Byte. So optimizing software for HDD won't go a…

NVMe drives which are approaching RAM speeds are a good compromise if RAM and server components are outside of your financial reach.

For a very generous definition of 'approaching'.

Re: RAM Is the New Disk

#37

Post by sand500 » Mon, Jul 31, 2017, 5:43 AM UTC

Ive wondered in estimation how much of "my" data is stored in various types of memory. CPU cache if I am actively browsing a website, those last couple IMs stored in the RAM of some server? Any content i have ever uploaded to the internet is probably on a hard disk ready to be brought to cache at a moments notice. Then there are all the backups on tape.

Re: RAM Is the New Disk

#38

Post by ericfrenkiel » Mon, Jul 31, 2017, 5:47 AM UTC

arielweisberg wrote: post #5

... I was the third engineer at VoltDB and spent six years making that bet. It's not a good bet. Maybe there are other factors, but if VoltDB could page out cold data to disk I think it would be at least 2x if not more successful. No one agreed with me so it never happened. I saw so many use cases go out the door because hey you know what? RAM is expensive and it's cheaper to page out cold data. The scale where that…

Yes, it's why we at MemSQL added a column store on disk in 2014. Memory-only is too limiting and has evolved to a notion of "memory-first."

Re: RAM Is the New Disk

#39

Post by hinkley » Mon, Jul 31, 2017, 5:49 AM UTC

sumanthvepa wrote: post #16

The problem with asking a programmer to keep track of the locality of their data, is that most modern programming languages make reasoning about locality hard to do. With the exception of C and C++. Even for those languages, unless all relevant data is in simple arrays, making assertions about locality is hard. For interpreted languages like Python or Javascript, figuring out RAM storage and access patterns of data i…

Lots of developers are blind to issues of local reasoning. It becomes a self fulfilling prophecy, because the code they write is often inscrutable. The people who generally can follow things like this can't anymore.

Re: RAM Is the New Disk

#40

Post by slackingoff2017 » Mon, Jul 31, 2017, 5:53 AM UTC

WalterBright wrote: post #25

Extensive use of "RAM" disks was commonplace in the 1980s.

And old is new again :). The ratio of ram to disk cost has historically varied wildly. The pendulum will come around again in a few years when huge SSD's are cheap.

I have a feeling with multi terabyte SSD's at cheaper prices we'll be shuffling all our data back to "disk" again :).