Re: Implementing Incremental View Maintenance

>> 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
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