On 21.10.21 12:55, Alexander Pyhalov wrote:
Now aggregates with internal states can be pushed down, if they are marked as pushdown safe (this flag is set to true for min/max/sum), have internal states and associated converters. Converters are called locally, they transform aggregate result to serialized internal representation. As converters don't have access to internal aggregate state, partial aggregates like avg() are still not pushable.
It seems to me that the system should be able to determine from the existing aggregate catalog entry whether an aggregate can be pushed down. For example, it could check aggtranstype != internal and similar. A separate boolean flag should not be necessary. Or if it is, the patch should provide some guidance about how an aggregate function author should set it.
