Tuning Authoritative Memory Usage

[Matt Corallo]

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