Tuning Authoritative Memory Usage

[Matt Corallo]

Hmm, they all have max-cache-size set to 8M (see config snippets in OP) but still show the divergent 
memory usage.

That said, I tried bumping one to 1024M on one of the smaller hosts and usage increased from ~270MB 
to ~437MB.

Matt

On 4/28/22 8:44 AM, Ondřej Surý wrote:
>  From top of my head - try setting the max-cache-size to infinite.  The internal views might still pre-allocate some stuff based on available memory.
> 
> Ondrej
> --
> Ondřej Surý (He/Him)
> ondrej at isc.org
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>> On 28. 4. 2022, at 17:26, Matt Corallo <bugmlmi at mattcorallo.com> wrote:
>>
>>
>>
>> On 4/27/22 9:19 AM, Petr Špaček wrote:
>>> On 27. 04. 22 16:04, Matt Corallo wrote:
>>>> I run a number of BIND9 (9.16-27-1~deb11u1 - Debian Stable) secondaries with some large zones (10s of DNSSEC-signed zones with ~100k records, not counting signatures, with a smattering of other zones). Somewhat to my surprise, even with "recursion no" the memory usage of instances is highly correlated with the hosts's available memory - BIN9 uses ~400M RSS on hosts with 1G of non-swap memory, but 2.3G on hosts with 4G of non-swap memory, all with identical configs and the same zones.
>>> Before we dive in, the general recommendation is:
>>> "If you are concerned about memory usage, upgrade to BIND 9.18." It has lot smaller memory footprint than 9.16.
>>> It can have many reasons, but **if the memory usage is not growing without bounds** then I'm betting it is just an artifact of the old memory allocator. It has a design quirk which causes it not return memory to OS (if it allocated in small blocks). As a result, the memory usage visible on OS level peaks at some value and then stays there.
>>> If that's what's happening you should see it in internal BIND statistics: Stats channel at URL /json/v1 shows value memory/InUse which will be significantly smaller than value seen by OS.
>>> In case the two values are close then you are seeing some other quirk and we need to dig deeper.
>>> Petr Špaček
>>> P.S. BIND 9.18 does not suffer from this, so I suggest you just upgrade and see.
>>
>> Upgraded to 9.18.2 and indeed memory usage is down double-digit-%, but the surprising host-dependent memory usage is still there - on hosts with 1G of non-swap memory bind is eating 470M, on hosts with 4G of non-swap memory 1.9G.
>>
>> This is right after startup, but at least with 9.16 I wasn't seeing any evidence of leaks. Indeed, heap fragmentation meant the memory usage increased a bit over time and then plateaued, but not by much, and ultimately the peak memory usage was still highly dependent on the host's available memory.
>>
>> Matt
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