>> One thing pending in this development line is how to catalogue aggregate >> functions that can be used in incrementally-maintainable views. >> I saw a brief mention somewhere that the devels knew it needed to be >> done, but I don't see in the thread that they got around to doing it. >> Did you guys have any thoughts on how it can be represented in catalogs? >> It seems sine-qua-non ... > > Yes, this is a pending issue. Currently, supported aggregate functions are > identified their name, that is, we support aggregate functions named "count", > "sum", "avg", "min", or "max". As mentioned before, this is not robust > because there might be user-defined aggregates with these names although all > built-in aggregates can be used in IVM. > > In our implementation, the new aggregate values are calculated using "+" and > "-" operations for sum and count, "/" for agv, and ">=" / "<=" for min/max. > Therefore, if there is a user-defined aggregate on a user-defined type which > doesn't support these operators, errors will raise. Obviously, this is a > problem. Even if these operators are defined, the semantics of user-defined > aggregate functions might not match with the way of maintaining views, and > resultant might be incorrect. > > I think there are at least three options to prevent these problems. > > In the first option, we support only built-in aggregates which we know able > to handle correctly. Supported aggregates can be identified using their OIDs. > User-defined aggregates are not supported. I think this is the simplest and > easiest way.
I think this is enough for the first cut of IVM. So +1. Best regards, -- Tatsuo Ishii SRA OSS, Inc. Japan English: http://www.sraoss.co.jp/index_en.php Japanese:http://www.sraoss.co.jp