Modifies the Private Aggregation API to merge histogram contributions with the same bucket and filtering ID before embedding in the aggregatable report's encrypted payload. Private Aggregation imposes a limit on the number of contributions that can be embedded in a single aggregatable report, with any additional contributions being dropped. By merging together contributions where possible, we can get additional utility out of the limit. Note that, ignoring the dropping of excess contributions, merging these sorts of contributions should not have any impact on the final outputs (i.e. summary reports).
Private Aggregation imposes a limit on the number of histogram contributions that can be embedded in a single aggregatable report, with any additional contributions being dropped. While we are considering increasing this limit (and allowing it to be customized), we can get additional utility out of any limit by “pre-aggregating” on the client. That is, we can merge any contributions that have the same bucket and same filtering ID. Note that, ignoring the dropping of excess contributions, merging these sorts of contributions should not have any impact on the final outputs (i.e. summary reports).
Explainers: https://github.com/patcg-individual-drafts/private-aggregation-api/pull/135