Static Allocation with Zig

https://nickmonad.blog/2025/static-allocation-with-zig-kv/

by todsacerdoti • 7 months ago

217 107 7 months ago

All memory must be statically allocated at startup. No memory may be dynamically allocated (or freed and reallocated) after initialization. This avoids unpredictable behavior that can significantly affect performance, and avoids use-after-free. As a second-order effect, it is our experience that this also makes for more efficient, simpler designs that are more performant and easier to maintain and reason about, compared to designs that do not consider all possible memory usage patterns upfront as part of the design. TigerStyle

It's baffling that a technique known for 30+ years in the industry have been repackage into "tiger style" or whatever this guru-esque thing this is.

addaon• 7 months ago

Yep. Those of us who write embedded code for a living call this “writing code.”

nickmonad7• 7 months ago

Author here! That's totally fair. I did learn this is a common technique in the embedded world and I had a whole section in the original draft about how it's not a super well-known technique in the typical "backend web server" world, but I wanted to keep the length of the post down so I cut that out. I think there's a lot we can learn from embedded code, especially around performance.

testdelacc1• 7 months ago

It is known, but not widely used outside of embedded programming. The fact that they’re using it while writing a database when they didn’t need to makes people sit up and notice. So why did they make this conscious choice?

It’s tempting to cut people down to size, but I don’t think it’s warranted here. I think TigerBeetle have created something remarkable and their approach to programming is how they’ve created it.

codys• 7 months ago

It seems it's just a part of a doc on style in tigerbeatle, in a similar way to the various "Google Style Guide" for code. These rarely have something new, but document what a particular project or organization does with respect to code style.

jandrewrogers• 7 months ago

Static allocation has been around for a long time but few people consider it even in contexts where it makes a lot of sense. I’ve designed a few database engines that used pure static allocation and developers often chafe at this model because it seems easier to delegate allocation (which really just obscures the complexity).

Allocation aside, many optimizations require knowing precisely how close to instantaneous resource limits the software actually is, so it is good practice for performance engineering generally.

Hardly anyone does it (look at most open source implementations) so promoting it can’t hurt.

wahern• 7 months ago

I've always thought static allocation was why we got overcommit[1] in Linux and its infamous OOM killer. In the 1990s big boy commercial databases assumed specialized admins, and one of their tasks was to figure out the value for the memory allocation setting in the DB configuration, which the DB would immediately allocate on startup. As a magic value, the easiest path forward was just to specify most of your RAM. DBs used to run on dedicated machines, anyhow. But then Linux came along and democratized running servers, and people wanted to run big boy databases alongside other services like Apache. Without overcommit these databases wouldn't run as typically configured--"best practice" allocation advice used up too much memory, leaving nothing for the rest of the services, especially on the more memory-constrained machines people ran Linux. Because on a typical system most of the memory preallocated to the DB was never used anyhow (the figure wasn't actually carefully chosen as intended), or the DB was designed (or at least the manual's written) with bigger machines in mind, and Linus wanted things to Just Work, whether experienced admins or not, the easy fix was just to overcommit in the kernel, et voila, a pain point for people dabbling with Linux was solved, at least superficially.

NB: I was just a newbie back then, so any older grey beards, please feel free to correct me. But I distinctly remember supporting commercial databases as being one of the justifications for overcommit, despite overcommit not being typical in the environments originally running those DBs, AFAIU.

[1] Note that AFAIU the BSDs had overcommit, too, but just for fork + CoW. Though these days FreeBSD at least has overcommit more similar to Linux. Solaris actually does strict accounting even for fork, and I assume that was true back in the 90s. Did any commercial Unices actually do overcommit by default?

mitchellh• 7 months ago

Snide and condescending (or at best: dismissive) comments like this help no one and can at the extremes stereotype an entire group in a bad light.

I think the more constructive reality is discussing why techniques that are common in some industries such as gaming or embedded systems have had difficulty being adopted more broadly, and celebrating that this idea which is good in many contexts is now spreading more broadly! Or, sharing some others that other industries might be missing out on (and again, asking critically why they aren't present).

Ideas in general require marketing to spread, that's literally what marketing is in the positive (in the negative its all sorts of slime!). If a coding standard used by a company is the marketing this idea needs to live and grow, then hell yeah, "tiger style" it is! Such is humanity.

pjmlp• 7 months ago

It was a common practice in 8 and 16 bit home computing.

brabel2• 7 months ago

had difficulty being adopted more broadly

Most applications don’t need to bother the user with things like how much memory they think will be needed upfront. They just allocate how much and when necessary. Most applications today are probably servers that change all the time. You would not know upfront how much memory you’d need as that would keep changing on every release! Static allocation may work in a few domains but it certainly doesn’t work in most.

astrobe_• 7 months ago

Because garbage-collected languages are easier to teach and to use. So the low-level, low-resource or high-performance stuff is left to a handful of specialists - or "insects" according to Heinlein. Speaking of old things, this reminds me of one of Asimov's short stories, where someone who rediscovers mental calculus is believed to be a genius.

kennykartman3• 7 months ago

Marketing is the thing that makes uninformed people adopt thing they don't need.

I dont think we need marketing, but rather education, which is the actually useful way to spread information.

If you think marketing is the way knowledge spreads, you'll end up with millions of dollars in your pocket and the belief that you have money because you're doing good, while the truth is that you have millions because you exploited others.

diimdeep• 7 months ago

Lord moral tuning fork, listen to this, the more marketing you throw at people the more you decrease SNR, until you hear nothing but "welcome to cosco we love you" advertisements and you live in the reality of the same movie this phrase is from.

publicdebates• 7 months ago

a technique known for 30+ years in the industry have been

Knowledge sharing with next generations is one of those very tricky things.

For one thing, how would I know where to find this? What book? What teacher? There are so many books, must I read all of them? What if my coworkers awaren't aware of it, how can they share it with me?

Also, an old saying goes, if you're good at something, never do it for free. This isn't exactly a trade secret, but how many people blog about every advanced technique and trick they know? I blogged about how to create real C function pointers from Lua closures, as a way to advertise for my product, but that could very well have been kept a trade secret (and probably should have, as I got 0 sales from that blog post still). Why would anyone want to share this "tiger style" knowledge with newer generations with no personal benefit? Aren't they incentivized to use it secretly, or maybe write it in a book, or blog about it for advertising?

Nevermark• 7 months ago

Trade secrets are not necessary to build up interest/visibility momentum. And likely "wasted" for external rewards, without pre-existing momentum.

(External = a marketing/sales bump. vs. Internal = enjoy sharing, writing to self-clarify, writing practice.)

Developing the abilities to repeatedly pick attractive topics (not as widely known as they are useful/interesting), and communicating (in a clear well-received voice/style), until those are validated by increasing visibility and sales/marketing impact, is where to start.

After that, the choice to share a trade secret can be made based on a more predictable reward trade off.

But every post already made, is a post to build on.

mytailorisrich• 7 months ago

I'd say usually you learn those techniques when you join a company as a junior dev and come in contact with engineers with decades of experience and systems that have been in production for years, too.

I think it's when people consider that anything more than 5 years old is ancient and dismiss it that we lose established techniques and knowledge that we are then bound to rediscover again and again.

matklad7• 7 months ago

To add more context, TigerStyle is quite a bit more than just static allocation, and it indeed explicitly attributes earlier work:

NASA's Power of Ten — Rules for Developing Safety Critical Code will change the way you code forever. To expand:

* https://github.com/tigerbeetle/tigerbeetle/blob/main/docs/TI...

* https://spinroot.com/gerard/pdf/P10.pdf

kibwen6• 7 months ago

Those guidelines are quite clear that they're written specifically in the context of the C programming language, and may not make sense in other contexts:

"For fairly pragmatic reasons, then, our coding rules primarily target C and attempt to optimize our ability to more thoroughly check the reliability of critical applications written in C."

A version of this document targeting, say, Ada would look quite different.

zozbot234• 7 months ago

All memory must be statically allocated at startup. No memory may be dynamically allocated (or freed and reallocated) after initialization ... It's baffling that a technique known for 30+ years in the industry have been repackaged

This is also how GPU shader programming works: there's no real equivalent to heap allocation or general pointers, you're expected to work as far as possible with local memory and sometimes preallocated shared buffers. So the technique may be quite relevant in the present day, even though it has a rather extensive history of its own.

array_key_first3• 7 months ago

I think it's more relevant than ever when most systems seem to dynamically allocate everything, some down to each individual object being its own runtime allocation, popularized by the likes of java.

On the surface it seems great: infinite scale and perfectly generic. The system can handle anything. But does it need to handle everything? And, what's the cost in terms of complexity of handling every single possible scenario?

ivanjermakov• 7 months ago

Related recent post from Tigerbeetle developer: https://matklad.github.io/2025/12/23/static-allocation-compi...

Zambyte• 7 months ago

I'm doing pretty much this exact pattern with NATS right now instead of Redis. Cool to see other people following similar strategies.

The fact that the Zig ecosystem follows the pattern set by the standard library to pass the Allocator interface around makes it super easy to write idiomatic code, and then decide on your allocation strategies at your call site. People have of course been doing this for decades in other languages, but it's not trivial to leverage existing ecosystems like libc while following this pattern, and your callees usually need to know something about the allocation strategy being used (even if only to avoid standard functions that do not follow that allocation strategy).

nickmonad7• 7 months ago

I have a few cases in this (proof of concept) codebase that require knowledge about allocation strategy, even in Zig, but that's on me and the design at this point. Something I wanted to touch on more in the post was the attempt to make the components of the system work with any kind of allocation strategy. I see a common thing in Zig projects today where something like `gpa: std.mem.Allocator` or even `arena: std.mem.Allocator` is used to signal intent, even though the allocator interface is generic.

d3ckard4• 7 months ago

Personally I believe static allocation has pretty huge consequences for theoretical computer science.

It’s the only kind of program that can be actually reasoned about. Also, not exactly Turing complete in classic sense.

Makes my little finitist heart get warm and fuzzy.

dnautics5• 7 months ago

i think you mean "exactly not Turing complete"

d3ckard4• 7 months ago

Nice correction :)

It’s actually quite tricky though. The allocation still happens and it’s not limited to, so you could plausibly argue both ways.

mikepurvis2• 7 months ago

I'm not an academic, but all those ByteArray linked lists have me feeling like this is less "static allocation" and more "I re-implemented a site-specific allocator and all that that implies".

Also it's giving me flashbacks to LwIP, which was a nightmare to debug when it would exhaust its preallocated buffer structures.

d3ckard4• 7 months ago

Personally, I see dynamic allocation more and more as a premature optimization and a historical wart.

We used to have very little memory, so we developed many tricks to handle it.

Now we have all the memory we need, but tricks remained. They are now more harmful than helpful.

Interestingly, embedded programming has a reputation for stability and AFAIK game development is also more and more about avoiding dynamic allocation.

kevin_thibedeau• 7 months ago

This is still a more dependable approach with resource constraints. Fragmentation is eliminated and you can monitor pools for usage in a worst case scenario. The only other risk here versus true static allocation is a memory leak which can be guarded against with suitable modern language design.

LwIPs buffers get passed around across interrupt handler boundaries in and out of various queues. That's that makes it hard to reason about. The allocation strategy is still sound when you can't risk using a heap.

kibwen6• 7 months ago

It’s the only kind of program that can be actually reasoned about.

Theoretically infinite memory isn't really the problem with reasoning about Turing-complete programs. In practice, the inability to guarantee that any program will halt still applies to any system with enough memory to do anything more than serve as an interesting toy.

I mean, I think this should be self-evident: our computers already do have finite memory. Giving a program slightly less memory to work with doesn't really change anything; you're still probably giving that statically-allocated program more memory than entire machines had in the 80s, and it's not like the limitations of computers in the 80s made us any better at reasoning about programs in general.

d3ckard4• 7 months ago

Yes, but allocations generate ever increasing combinatorial space of possible failure modes.

Static allocation requires you to explicitly handle overflows, but also by centralizing them, you probably need not to have as many handlers.

Technically, all of this can happen as well in language with allocations. It’s just that you can’t force the behavior.

IshKebab• 7 months ago

It’s the only kind of program that can be actually reasoned about.

What do you mean? There are loads of formal reasoning tools that use dynamic allocation, e.g. Lean.

muvlon2• 7 months ago

It’s the only kind of program that can be actually reasoned about.

No. That is one restriction that allows you to theoretically escape the halting problem, but not the only one. Total functional programming languages for example do it by restricting recursion to a weaker form.

Also, more generally, we can reason about plenty of programs written in entirely Turing complete languages/styles. People keep mistaking the halting problem as saying that we can never successfully do termination analysis on any program. We can, on many practical programs, including ones that do dynamic allocations.

Conversely, there are programs that use only a statically bounded amount of memory for which this analysis is entirely out of reach. For example, you can write one that checks the Collatz conjecture for the first 2^1000 integers that only needs about a page of memory.

loeg• 7 months ago

We do a lazier version of this with a service at work. All of the large buffers and caches are statically (runtime-configured) sized, but various internal data structures assumed to be approximately de minimis can use the standard allocator to add items without worrying about it.

nromiun• 7 months ago

All memory must be statically allocated at startup.

But why? If you do that you are just taking memory away from other processes. Is there any significant speed improvement over just dynamic allocation?

AnimalMuppet• 7 months ago

1. On modern OSes, you probably aren't "taking it away from other processes" until you actually use it. Statically allocated but untouched memory is probably just an entry in a page table somewhere.

2. Speed improvement? No. The improvement is in your ability to reason about memory usage, and about time usage. Dynamic allocations add a very much non-deterministic amount of time to whatever you're doing.

Ericson23142• 7 months ago

If you use it and stop using it, the OS cannot reclaim the pages, because it doesn't know that you've stopped. At best, it can offload the memory to disk, but this waste disk space, and also time for pointless writes.

kibwen6• 7 months ago

On modern OSes, you probably aren't "taking it away from other processes" until you actually use it.

But if you're assuming that overcommit is what will save you from wasting memory in this way, then that sabotages the whole idea of using this scheme in order to avoid potential allocation errors.

jeffreygoesto• 7 months ago

Using this as well in embddded. The whole point is to commit and lock the pages after allocation, to not experience what you correctly describe. You want to have a single checkpoint after which you simply can stop worrying about oom.

jrmg• 7 months ago

In response to (1) - you’re right, but that also implies that the added safety from static allocation when running on a modern OS is just an illusion: the OS may be unable to supply a fresh page from your ‘statically allocated’ memory when you actually write to it and it has to be backed by something real. The real stuff may have run out.

pastage• 7 months ago

Use mlock as long as it is allocated it is going to be rather deterministic, of course you might be running in a VM on an over commited host. I guess you can "prefault" in a busy loop instead of only on startup, waste memory and cpu!

matklad7• 7 months ago

See https://github.com/tigerbeetle/tigerbeetle/blob/main/docs/TI... for motivation.

- Operational predictability --- latencies stay put, the risk of threshing is reduced (_other_ applications on the box can still misbehave, but you are probably using a dedicated box for a key database)

- Forcing function to avoid use-after-free. Zig doesn't have a borrow checker, so you need something else in its place. Static allocation is a large part of TigerBeetle's something else.

- Forcing function to ensure existence of application-level limits. This is tricky to explain, but static allocation is a _consequence_ of everything else being limited. And having everything limited helps ensure smooth operations when the load approaches deployment limit.

- Code simplification. Surprisingly, static allocation is just easier than dynamic. It has the same "anti-soup-of-pointers" property as Rust's borrow checker.

pron4• 7 months ago

Forcing function to avoid use-after-free

Doesn't reusing memory effectively allow for use-after-free, only at the progam level (even with a borrow checker)?

dale-cooper• 7 months ago

Maybe I'm missing something, but two thoughts:

1. Doesn't the overcommit feature lessen the benefits of this? Your initial allocation works but you can still run out of memory at runtime.

2. For a KV store, you'd still be at risk of application level use-after-free bugs since you need to keep track of what of your statically allocated memory is in use or not?

nickmonad7• 7 months ago

Author here! Overcommit is definitely a thing to watch out for. I believe TigerBeetle calls this out in their documentation. I think you'd have to explicitly disable it on Linux.

For the second question, yes, we have to keep track of what's in use. The keys and values are allocated via a memory pool that uses a free-list to keep track of what's available. When a request to add a key/value pair comes in, we first check if we have space (i.e. available buffers) in both the key pool and value pool. Once those are marked as "reserved", the free-list kind of forgets about them until the buffer is released back into the pool. Hopefully that helps!

justincormack• 7 months ago

You can work around overcommit by writing a byte to every allocated page at allocation time, so that it has to be actually allocated.

dnautics5• 7 months ago

out of curiosity, does that generally mean that (linux) OOM killer can't get you? IIRC the oom killer is only triggered on new page request, and only the requesting process is eligble for the murder?

kristoff_it• 7 months ago

A coincidental counterpart to this project is my zero allocation Redis client. If kv supports RESPv3 then it should work without issue :^)

https://github.com/kristoff-it/zig-okredis

nickmonad7• 7 months ago

Nice! Will definitely take a look :)

lazy-lambda• 7 months ago

No mention of AI - such a good post.

MatthiasPortzel• 7 months ago

One key thing to understand about TigerBeetle is that it's a file-system-backed database. Static allocation means they limit the number of resources in memory at once (number of connections, number of records that can be returned from a single query, etc). One of the points is that these things are limited in practice anyways (MySQL and Postgres have a simultaneous connection limit, applications should implement pagination). Thinking about and specifying these limits up front is better than having operations time out or OOM. On the other hand, TigerBeetle does not impose any limit on the amount of data that can be stored in the database.

=> https://tigerbeetle.com/blog/2022-10-12-a-database-without-d...

It's always bad to use O(N) memory if you don't have to. With a FS-backed database, you don't have to. (Whether you're using static allocation or not. I work on a Ruby web-app, and we avoid loading N records into memory at once, using fixed-sized batches instead.) Doing allocation up front is just a very nice way of ensuring you've thought about those limits, and making sure you don't slip up, and avoiding the runtime cost of allocations.

This is totally different from OP's situation, where they're implementing an in-memory database. This means that 1) they've had to impose a limit on the number of kv-pairs they store, and 2) they're paying the cost for all kv-pairs at startup. This is only acceptable if you know you have a fixed upper bound on the number of kv-pairs to store.

levkk• 7 months ago

That makes sense. For example, your redis instance will have fixed RAM, so might as well pre-allocate it at boot and avoid fragmentation.

Memcached works similarly (slabs of fixed size), except they are not pre-allocated.

If you're sharing hardware with multiple services, e.g. web, database, cache, the kind of performance this is targeting isn't a priority.

matklad7• 7 months ago

Yes, very good point, thanks!

As a tiny nit, TigerBeetle isn't _file system_ backed database, we intentionally limit ourselves to a single "file", and can work with a raw block device or partition, without file system involvement.

fsckboy• 7 months ago

we intentionally limit ourselves to a single "file", and can work with a raw block device or partition, without file system involvement

those features all go together as one thing. and it's the unix way of accessing block devices (and their interchangeability with streams from the client software perspective)

you're right, it's not the file system.

netik• 7 months ago

Didn’t we solve this already with slab allocators in memcached? The major problem with fixed allocation like this is fragmentation in memory over time, which you then have to reinvent GC for.

TheMagicHorsey• 7 months ago

In a strange coincidence (or maybe its actually inevitable given the timing) I also saw a podcast with Matklad of Tigerbeetle and had a similar idea--I've been working on a massively multiplayer game as a hobby project, also built in zig, also fully allocating all memory at startup, and also had an experience almost identical to OP's. In my case both my client and server are in Zig. Zig is pretty great at doing performant game code (rendering and physics on the client) ... it's less great on the server compared to Go (early days and fewer batteries included, fewer things just work out of the box ... but you can find pretty much everything you need for a game server with a little hunting and pecking and a debugging few build issues).

Zig also works "okay" with vibe coding. Golang works much better (maybe a function of the models I use (primarily through Cursor) or maybe its that there's less Zig code out in the wild for models to scrape and learn from, or maybe idiomatic Zig just isn't a thing yet the way it is with Go. Not quite sure.

dnautics5• 7 months ago

claude is really good at zig.

amount of examples on the web is not a good predictor of llm capability, since we know you can poison an llm with ~250 examples. it doesn't take much.

xthe• 7 months ago

Nice write-up. Static allocation forcing you to think about limits up front feels like a real design win

ogogmad• 7 months ago

This might be a silly thing to point out, but where do people draw the line between an allocation happening or not happening? You still need to track vacant/occupied memory even when there's no OS or other programs around. It's especially bewildering when people claim that some database program "doesn't allocate".

nickmonad7• 7 months ago

This is the fundamental question which motivated the post. :)

I think there are a few different ways to approach the answer, and it kind of depends on what you mean by "draw the line between an allocation happening or not happening." At the surface level, Zig makes this relatively easy, since you can grep for all instances of `std.mem.Allocator` and see where those allocations are occurring throughout the codebase. This only gets you so far though, because some of those Allocator instances could be backed by something like a FixedBufferAllocator, which uses already allocated memory either from the stack or the heap. So the usage of the Allocator instance at the interface level doesn't actually tell you "this is for sure allocating memory from the OS." You have to consider it in the larger context of the system.

And yes, we do still need to track vacant/occupied memory, we just do it at the application level. At that level, the OS sees it all as "occupied". For example, in kv, the connection buffer space is marked as vacant/occupied using a memory pool at runtime. But, that pool was allocated from the OS during initialization. As we use the pool we just have to do some very basic bookkeeping using a free-list. That determines if a new connection can actually be accepted or not.

Hopefully that helps. Ultimately, we do allocate, it just happens right away during initialization and that allocated space is reused throughout program execution. But, it doesn't have to be nearly as complicated as "reinventing garbage collection" as I've seen some other comments mention.

CashWasabi2• 7 months ago

This also works well for games. I use a FixedBufferAllocator that allocates everything except assets upfront (systems, entities, etc.). Tigerstyle is a good starting point for efficient and debuggable software.Thanks for the article!

CashWasabi2• 7 months ago

Great read! I'm doing something similar with my game engine. I use a FixedBufferAllocator for static allocation and initialize/allocate all my systems and entities with the necessary size at the start. The only exception currently is asset loading because this can be quite dynamic at times.

Static Allocation with Zig

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