Private Aggregation API Per Buyer Latency Stats

[maleangrubb]

Hello,

We've implemented the debug mode version for per buyer latency stats as a seller for FLEDGE and have noticed a few issues that limit its usefulness.

To start with, the 20 report per auction limit with a test auction including 36 opted-in IGs resulted in us receiving seller reports solely for the # of IGs and 19 total signals fetch latencies, with no generateBid() latency or # of bids counts at all. The 20 report limit per auction, I assume. Could this be increased?

Note that the external docs communicated that the generateBid() and signals fetch latencies would be sums per interest group owner and not per interest group as we received.

If it cannot be increased, perhaps the reports sent could be divided to give more useful data: i.e. 1 with the # of IGs, 1 with the # of bids, and the remaining X be split between sampled generateBid() and trusted scoring latency results on a per IG owner basis?

Is this something that could be considered?

[alexmturner]

Hi @maleangrubb, looks like you've already found it, but just want to explicitly highlight that patcg-individual-drafts/private-aggregation-api#81 has some recent discussion about this problem.

To briefly summarize, we're discussing increasing the default limit to 100, making this limit customizable, and pre-aggregating (i.e. merging) contributions that have the same bucket (and filtering ID). Increasing the number of reports is something we considered earlier, but unfortunately would require some privacy mitigations.

[morlovich]

So to be honest, I am a bit unclear as to how best to deal with this when it comes to backwards compatibility: the changes required are quite massive, but maybe things are sufficiently bad that maybe it's OK to totally change them since no one is actually using them. There are also subtler semantic issues involved since a lot of these things really are per bid when it comes to how the API can generally be used (rather than how it's normally used).

However, there also has been design sketching going on designing improvements to metrics directly available to the buyers (rather than those delegated to sellers), which contains considerable overlap with this issue, in that it wants to measure some of the same things. Those metrics could also be potentially be made delegatable to sellers via capabilities (though we would have to be careful to make sure they're actually usable since delegated metrics are a lot less flexible in data format). Anyway, the point is that there is a document at https://docs.google.com/document/d/1EHVJkKUKIL4dMFrcJ6FJH65Ad4Ml7pKZ8Iepft5OvYk/edit#heading=h.pw9khvaqdru9
... productive feedback on which would be very much appreciated.

[alexmturner]

To follow up, the client-side contribution merging (i.e. pre-aggregation) feature is being rolled out as part of M129 (see here for more detail).