[schema] aggregation-share/sum-part has incorrect cardinality of sum and batch_uuid

[yuriks]

In the original protobuf schema defined in the IDL document, PrioSumPart contained a single bytes value_sum field, and a repeated batch_uuid list. The batch_uuid list represents the uuids of all of the batches (tracing back to the ingestor) that participated in this aggregation.

At some point in the conversion to Avro, this got flipped and the current schema now has only a single batch_uuid, but an array of sums.

Not only does this not let us properly represent the batch_uuids when we do the final multi-batch reduction sum, the sums array will also always contain only one value (because all aggregations we'll do always produce a single output sum per file, both the per-batch sum, and the overall sum for a given time range), so this seems like an oversight and should be fixed to match the intent of the original schema.

[tlepoint]

Actually, the sums array needs to be an array, because the sum is done over a vector containing n bins. We can choose the terminology that you prefer (one sum of a vector, or many individual sums, the current avro file choosing the latter formulation). In the original proto schema, sum was represented as bytes (assuming proper serialization): I modified this to be int64 to be consistent with the f_r, g_r, h_r, and r_pit terms.

Thanks for catching the error for the batch_uuid, this indeed should be an array. I may have been thrown off by the comment above the batch_uuid field.

[tgeoghegan]

You're quite right @tlepoint, and Yuri and I realized as much last Friday, but failed to say as much in this issue. I think what I currently have in #2 is consistent with what you're saying.

[tgeoghegan]

Addressed in #2. Please file a new issue for further schema amendments, referencing this one if necessary.