7 ms·
Preparing for the .NET 10 GC
- jcmontx 1y agoBut don't you take a hit in performance by running the GC more often?
- NetMageSCW 1y agoNot necessarily if you have more (so smaller) heaps so each GC takes less time.
- deleted 1y ago[deleted]
- stonemetal12 1y agoMaybe, maybe not. If GC is a O(n^2) then running it twice at n=5 is a much shorter run time than once at n=10.
- orphea 1y agoFor those who like me was left wondering what DATAS is, here is the link: https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/datas https://learn.microsoft.com/en-us/dotnet/standard/garbage-co...
- gwbas1c 1y agoYeah, I kept scrolling to the top to see if I overlooked something. Then I realized, "oh, it's hosted on Medium." (I generally find Medium posts to be very low quality.) In this case, the author implies that they are on the .Net team, so I'm continuing to read. (At least I hope the author actually is on the .Net team and isn't blowing hot air, because it's a Medium post and not something from an official MS blog.)
- olidb 1y agoMaoni Stephens is indeed on the .net team and is, as far as I know, the lead architect of the .net garbabe collector for many years: https://github.com/Maoni0 https://github.com/Maoni0 https://devblogs.microsoft.com/dotnet/author/maoni/ https://devblogs.microsoft.com/dotnet/author/maoni/ Therefore she's probably the person with the most knowledge about the .net GC but maybe not the best writer (I haven't read the article yet).
- moomin 1y agoThe writing itself is fine, but she’s assuming a LOT of knowledge e.g. what a GC0 budget is and what increasing it means.
- lomase 1y agoI did not even know Server GC was a thing.
- mrcsharp 1y agoDid it get you curious enough to go look that up?
- moomin 1y agoIt did indeed! :D
- mrcsharp 1y agoGreat! Same here. It was a great read overall. My current use-case won't benefit from DATAS (using Azure App Service), it's good to know this option exists though. Actually, thinking about this more, this is super helpful for Stage VMs that are shared among multiple projects. It can help pack more instances in those VMs.
- bob1029 1y ago> Maximum throughput (measured in RPS) shows a 2-3% reduction, but with a working set improvement of over 80%. I have a hard time finding this approach compelling. The amount of additional GC required in their example seems extreme to me.
- neonsunset 1y ago[dead]
- bilekas 1y agoIt's incredibly frustrating the author doesn't actually say "Garbage Collector (GC)" I'm aware but something niggling in the back of my head had me second guessing.
- nu11ptr 1y agoEven worse: they don't explain what the DATAS acronym means. Seems like the author makes too many assumptions about the knowledge base of their reader IMO.
- stonemetal12 1y agoI am guessing he doesn't expect linking from outside. The blog post before this one starts: "In this blog post I’m going to talk about our .NET 8.0 GC feature called DATAS (Dynamic Adaptation To Application Sizes)."
- Akronymus 1y agoBecause everyone knows at least the formulas for quartz, of course https://xkcd.com/2501/ https://xkcd.com/2501/
- graycat 1y agoBasic rule in technical writing: For obscure terminology, always define and explain that (e.g., maybe with a reference) before using it.
- gwbas1c 1y agoThis post would carry a lot more authority if it was on an official MS or .net blog; instead of Medium. (I typically associate Medium with low-quality blog entries and don't read them.)
- nu11ptr 1y agoI don't generally find them low quality, but I do wish people wouldn't use it since I don't subscribe to it.
- giancarlostoro 1y agoIts the Pinterest of blogs, its really annoying.
- justin66 1y agoOr if the author used their real name.
- giancarlostoro 1y agoAgree. It's not like a blogpost that is about grey hat subjects or something.
- artimaeis 1y agoFor what it's worth, Maoni is the author's real name. Maoni0 is what they go by everywhere. You can find interviews and plenty of their other content if you search around a bit.
- justin66 1y agoUsing a handle instead of their full name on an article is a choice. The first impression is not “knowledgeable employee making post about company’s product.” Posting from a Microsoft blog would to some extent fix this, to the OP’s point. (I know - who cares. But first impressions are what they are)
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- gwbas1c 1y agoOne anecdote from working with .Net for over 20 years: I've had a few situations where someone (who isn't a programmer and/or doesn't work with .Net) insists that the application has a memory leak. First, I explain that garbage collected applications don't release memory immediately. Then I get sucked into a wild goose chase looking for a memory leak that doesn't exist. Finally, I point out that the behavior they see is normal, usually to some grumbling. From what I can tell, DATAS basically makes a .Net application have a normal memory footprint. Otherwise, .Net is quite a pig when it comes to memory. https://github.com/GWBasic/soft_matrix https://github.com/GWBasic/soft_matrix, implemented in Rust, generally has very low memory consumption. An earlier version that I wrote in C# would consume gigabytes of memory (and often run out of memory when run on Mono with the Bohem garbage collector.) --- > If startup perf is critical, DATAS is not for you This is one of my big frustrations with .net, (although I tend to look at how dependency injection is implemented as a bigger culprit.) It does make me wonder: How practical is it to just use traditional reference counting and then periodically do a mark-and-sweep? I know it's a very different approach than .net was designed for. (Because they deliberately decided that dereferencing an object should have no computational cost.) It's more of a rhetorical question.
- nu11ptr 1y ago> It does make me wonder: How practical is it to just use traditional reference counting and then periodically do a mark-and-sweep? I know it's a very different approach than .net was designed for. (Because they deliberately decided that dereferencing an object should have no computational cost.) It's more of a rhetorical question. This is what CPython does. The trade off is solidly worse allocator performance, however. You also have the reference counting overhead, which is not trivial unless it is deferred. There is always a connection between the allocator and collector. If you use a compacting collector (which I assumed .NET does), you get bump pointer allocation, which is very fast. However, if you use a non-compacting collector (mark-and-sweep is non-compacting), you would then fallback to a normal free list allocator (aka as "malloc") which has solidly higher overhead. You can see the impact of this (and reference counting) in any benchmark that builds a tree (and therefore is highly contended on allocation). This is also why languages that use free list allocation often have some sort of "arena" library, so they can have high speed bump pointer allocation in hot spots (and then free all that memory at once later on). BTW, reference counting, malloc/free performance also impact Rust, but given Rust's heavy reliance on the stack it often doesn't impact performance much (aka just doing less allocations). For allocation heavy code, many of us use MiMalloc one of the better malloc/free implementations.
- daxfohl 1y agoMaybe I missed it, but is there a shadow mode to estimate the memory and perf impact without actually enabling the feature? Or better yet, a way to analyze existing dotnet 8 GC logs to understand the approx impact?
- mrcsharp 1y agoBenchmarking is the best way to go here. Enabling/disabling DATAS, Server GC, and Workstation GC is pretty straightforward anyways.
- graycat 1y agoFor the author, some definitions: GC? -- Maybe "Garbage Collection", i.e., have some memory (mainly computer main memory) allocated, don't need it (just now or forever), and want to release it, i.e., no longer have it allocated for its original purpose. By releasing can make it available for other purposes, software threads, programs, virtual machines, etc. DATAS? -- Not a spelling error or about any usual meaning for data and instead is as in https://learn.microsoft.com/en-us/dotnet/standard/garbage-collection/datas https://learn.microsoft.com/en-us/dotnet/standard/garbage-co... for "Dynamic adaptation to application sizes" So, we're trying to take actions over time in response to some inputs that are in some respects unpredictable. Okay, what is the objective, i.e., the reason, what we hope to gain, or why bother? And for the part that is somewhat unpredictable over time, that's one or more stochastic processes (or one multidimensional stochastic process?). So, in broad terms, we are interested in stochastic optimal control. "Dynamic adaptation", is close and also close to one method, dynamic programming -- in an earlier thread at Hacker News, gave a list of references. Confession, wrote my applied math Ph.D. dissertation in that subject. Hmm, how to proceed??? Maybe, (A) Know more about the context, e.g., what the computer is doing, what's to be minimized or maximized. (B) Collect some data on the way to knowing more about the stochastic processes involved. For me, how to get paid? If tried to make a living from applied stochastic optimal control, would have died from starvation. Got the Ph.D. JUST to be better prepared as an employee for such problems and had to learn that NO one, not even one in the galaxy, cares as much as one photon of ~1 Hz light. So, am starting a business heavily in computing and applied math. The code from Microsoft tools is all in .NET, ASP.NET, ADO.NET, etc. Code runs fine. The .NET software, via the VB.NET syntactic sugar, is GREAT for writing the code. So, MUST keep up on Microsoft tools, and here just did that. Since .NET 10 is changing some versions of Windows, my reaction is (i) add a lot of main memory until GC is nearly irrelevant, (ii) in general, wait a few years to give Microsoft time to fix problems, i.e., usually be a few years behind the latest versions, i.e., to "Prepare for .NET 10", first wait a few years. Experience: At one time, saw some server farms big on reliability. One site had two of everything, one for the real work and another to test the latest for bugs before being used for real work. Another had their own electrical power, Diesel generators ~30 feet high, a second site duplicating everything, ~400 miles away, with every site with lots of redundancy. In such contexts, working hard and taking risks trying to save money on main memory seem unwise.
- kg 1y agoSome translations for acronyms and terms from this post (sourced from the glossary in dotnet/runtime along with source code grepping): GC: Garbage Collector DATAS: Dynamic adaptation to application sizes UOH: User Old Heap. I can't find an explanation for what this is. LOH: Large Object Heap. This is where allocations over a size threshold go in .NET. POH: Pinned Object Heap. Pinning is used to stop an object in the GC's memory from being moved around by the GC (for compaction). ASP.net: Active Server Pages for .NET. This is a framework for building web applications using .NET, a successor to the classic ASP which was built on COM and scripting languages like JScript/VBScript. Workstation / Server GC: .NET has two major GC modes which have different configurations for things like having per-cpu-core segregated heaps, doing background or foreground GCs, etc. This is designed to optimize for different workloads, like running a webserver vs a graphical application. Ephemeral GC / Ephemeral generation: To quote the docs: > For small objects the heap is divided into 3 generations: gen0, gen1 and gen2. For large objects there's one generation – gen3. Gen0 and gen1 are referred to as ephemeral (objects lasting for a short time) generations. Essentially, generation 0 or gen0 is where brand new objects live. If the GC sees that gen0 objects have survived when it does a collection, it promotes them to gen1, and then they will eventually get promoted to gen2. Most temporary objects live and die in gen0. Pause time: Most garbage collectors will need to pause the whole application in order to run, though they may not need the application to stay paused the whole time they are working. So pause time and % pause time track how much time the application spends paused for the GC to do its job; ideally these values are low. BCD: Quoting the post: > 1) introduced a concept of “Budget Computed via DATAS (BCD)” which is calculated based on the application size and gives us an upper bound of the gen0 budget for that size, which can approximate the generation size for gen0 Essentially, this is an estimate of how much space the ephemeral generation (temporary objects plus some extras) is using. TCP: Quoting the post again: > 2) within this upper bound, we can further reduce memory if we can still maintain reasonable performance. And we define this “reasonable performance” with a target Throughput Cost Percentage (TCP). This takes into consideration both GC pauses and how much allocating threads have to wait.
- moomin 1y agoGood guide. I _think_ UOH is “unpinned object heap”, which is a variant of the large object heap that allows compaction. So the only things going into the LOH these days are both large and pinned. But I’m not 100% on this.