Solving the Cardano node huge memory usage - done

sorry. the quote above…

“I think that GHC 9.2 with the new -Fd , -I0.3 (the default) and -Iw600 will solve this issue completely as it will allow releasing memory to the OS which never happen with GHC 8.10.x.”

i was wondering when GHC 9.2 would be released, and more importantly, how would i get it? would this be a git pull and rebuild?


It’s difficult to trigger the problematic behavior on purpose. Certain of my relays did experience this “heap leak” and start swapping after just 12h some after 3 days and some never (like your relay which was up for 3 weeks with constant RAM usage). Now it’s true that none of my relays have 16Gb of RAM so GHC’s RTS might indeed behave differently depending on the amount of free RAM you have, or depending on your GNU/Linux distro.
It may also depend on the kind of requests your node gets from the Internet or locally (ledger dumps for example), etc… If you can already run your nodes for 3 weeks without increasing RAM usage, then you probably do not need this solution, at least for now. At first only one of my relays was experiencing this then a few monts later a second… At some point I even thought that I was victim of a kind of DOS attack.

You need to check GHC’s website for that then IOG probably will have to update their build to allow 9.2 to be used (there can be breaking changes between major versions of GHC). Once it’s released you just need to install it and build the node with it following the usual instructions with the proper modification to change the compiler version.

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Interesting work.

We’ve always found memory management to be fine (excepting one leak which was quickly fixed about 5 node versions ago). Cardano-node will use what memory you give it over time (lazy collection) up to about 20GB. For busy relays keeping track of 60+ connections inbound and outbound we like to allow 16GB. For block producers 10-12GB is fine.

You can get by on less (the minimum spec is 8GB) but these numbers give us a very stable setup.

Hi 2072,

Thanks for posting this. I’ve been very interested in heap size / garbage collection tuning in Java as from my experience it can indeed make a world of difference. I have no experience with this in Haskell though.

I was wondering, do you know what the application throughput is with the default GC parameters?

I understand Haskell will inherently produce more garbage since it is a true functional language. An application throughput of just 64% seems low when compared to the numbers I’m used to in Java. That’s why I am wondering. :slight_smile:

Thanks in advance!

I got the following after running a relay with default parameters for an hour.

 22380288   1225752   2285880  0.204  0.209   80.196 4146.292    0    0  (Gen:  1)
     3736                      0.000  0.000

  36,327,280,448 bytes allocated in the heap
   8,365,121,336 bytes copied during GC
   1,552,878,096 bytes maximum residency (20 sample(s))
      31,581,680 bytes maximum slop
            3099 MiB total memory in use (0 MB lost due to fragmentation)

                                     Tot time (elapsed)  Avg pause  Max pause
  Gen  0      1197 colls,  1197 par   13.495s   6.840s     0.0057s    0.0697s
  Gen  1        20 colls,    19 par    7.179s   3.752s     0.1876s    1.6108s

  Parallel GC work balance: 33.57% (serial 0%, perfect 100%)

  TASKS: 17 (1 bound, 14 peak workers (16 total), using -N2)

  SPARKS: 0 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 0 fizzled)

  INIT    time    0.002s  (  0.002s elapsed)
  MUT     time   59.519s  (4135.698s elapsed)
  GC      time   20.674s  ( 10.592s elapsed)
  EXIT    time    0.004s  (  0.009s elapsed)
  Total   time   80.199s  (4146.300s elapsed)

  Alloc rate    610,346,326 bytes per MUT second

  Productivity  74.2% of total user, 99.7% of total elapsed

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What’s the reason that it’s configured to only use 2 cores? Will allocating more be a problem or is that just unnecessary?

This is exactly why Cardano delegators should support small decentralized pools. By supporting a wider range of pools, delegators promote more insights into the better running of the Cardano system. Just chasing perceived better returns, supporting dubious missions or following the latest influencer is not enough to ensure that Cardano reaches its full potential or even survives.


Thank you so much for this, this is amazing work!

This may be a dumb question but with the -N parameter, do you have two cpus in your one relay? if I had one cpu in the relay would I set it to -N1. Or is this parameter for your node as a whole eg relay, relay and BP? I am just quite surprised if you have two cpus in the one relay haha.

If you have a node that uses up to 20GB it would be really interesting to try those parameters and tell us the results.

No I have not made that test but from my observation this can vary a lot depending on the relays, I’m not sure why (probably depends on the kind of work and various system hardware specificities).

for example, my most efficient relay is at 80% of productivity while the median is 65%, the worst one is a raspberry pie with only 34% (probably because memory copy and move are much slower on this kind of hardware where GHC is still using LLVM to compile as far as I know…).

The problem is that each major GC implies to copy the whole live data each time (around 3Gb) even if there is nothing to collect because with these settings a major GC is forced every 10 minutes if the node is not busy. So this productivity rating just shows that CPU is wasted doing GCs while the program is idle.

-N2 is the default setting the node is compiled with, maybe they don’t know that -N without a number use all the CPUs available, or maybe this is a new GHC feature, or they find -N2 is enough… Only IOG can answer to this question. I have several nodes running with -N4 without problem.


Like the others here I just wanted to thank you for sharing this information that you clearly put a lot of effort into uncovering.

It’s fascinating and benefits everyone to better understand the systems we’re using and how they can be optimized. Your attitude about it is also impressive, and I think says a lot about you and this community. I truly sympathize with the sentiment of your intro and I’ve already recommended your pool to a few people :slight_smile:

Well done and thank you again!

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