Re: Is there an efficient way to delete multiple elements from a set?

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Thu, Feb 01, 2024 at 10:41:21AM +0100, Pablo Neira Ayuso wrote:
> On Wed, Jan 31, 2024 at 10:14:41AM +0200, Anton wrote:
> > Hello, I've been experimenting with nftables sets for the purpose of
> > geoip blocking. Let's say I'd like to add ip blocks for multiple
> > countries to a blacklist or to a whitelist. Perhaps the most efficient
> > way to do that would be by combining all required ip blocks in one set
> > (for each family). However since country ip blocks are a moving
> > target, I would need to regularly refresh parts of that set. My idea
> > was to delete all ip addresses corresponding to an ip block from the
> > set and then add the updated ip block. The problem is, this is very
> > slow. While adding an ip block takes (in my VM) 0.09s, deleting all
> > ip's from that same block takes 14.5s.
> > 
> > This is how I'm doing the deletion and the time measurement:
> > printf '%s\n' "delete element inet test testset { $(cat test.set) };"
> > | /usr/bin/time -f %es nft -f -
> > 
> > (the test.set file stores a comma-separated list of subnets)
> > 
> > Is there a more efficient way to do this? I could of course flush the
> > set and rebuild it every time I need to update some part of it, but I
> > thought I'd ask before deciding to implement that.
> 
> It is possible to flush the set and fill up with content again:
> 
> flush set inet test testset
> add element inet test testset { ...  }

I forgot to mention: Run this a batch .nft file, then:

        # nft -f update-set.nft