Hai

> On 21 Dec 2016, at 15:26, Alberto Ferrari <aferrari@starconnecting.com> wrote:
>
> Imad, we had the same problem (you can find our mail in list with
> subject "Functions in Monetdb", date nov/22), and had no satisfactory
> solution yet.
> I think monetDb is not good for UDF yet... (though is great db engine!)

Mostly, it’s because monetdb can’t automatically bulk execute user defined functions.
So for UDFs, the overhead of a function call is multiplied by the number of values to process.
While for built-in functions, they all have a bulk version, so that they are only called once with all values to process.

>
>
>
> 2016-12-21 10:40 GMT-03:00 imad hajj chahine <imad.hajj.chahine@gmail.com>:
>> Hi,
>>
>> I have a weird behavior when i package some sql code in a function, the
>> performance deteriorate.
>> The same code running directly in select statement is blinking fast.
>> ex:
>>
>> select date_to_str("Expiry_Date",'%Y-%m-%d') from table: exec time is 0.72s
>>
>> if i create a function:
>> CREATE FUNCTION DayBracket(pdate date) returns char(10)
>> BEGIN
>>    return date_to_str(pdate,'%Y-%m-%d');
>> end;
>> grant execute on function DayBracket to public;
>>
>> and execute select DayBracket("Expiry_Date") from table: exec time is 24s
>>
>> even when i set the limit to 1 its taking the same time, so i guess it
>> should be something related to loading the function.

Using LIMIT in the outer query doesn’t help, your UDF is till called with every value.
The final tuple is only filtered after that.

>>
>> The following function perform much better:
>> CREATE FUNCTION DayBracketOpt(pdate date) returns char(10)
>> BEGIN
>>    return extract(year from pdate) || '-' || lpad(extract(month from
>> pdate),2,'0') || '-' || lpad(dayofmonth(pdate),2,'0');
>> end;
>> grant execute on function DayBracketOpt to public;

Hmm, a bit unexpected.  How much better is it?  How many values are processed?

>>
>> I also tried to create a Python function:
>> CREATE FUNCTION pyDayBracket(pdate date) returns string
>> LANGUAGE PYTHON {
>> from time import strftime, strptime
>> return [strftime("%Y-%m-%d", strptime(pdt,"%Y-%m-%d")) for pdt in pdate]
>> };
>> it is taking too long and throwing an exception:buffer size mismatch
>> PS: the pdate array type is detected in pythons as string not as date;
>>
>>
>> Also how to delete a function with dependency, I need to replace some
>> functions which are used in others functions and views. Any flags to turn
>> off dependency check before dropping?

I think you’ll have to drop the depending functions and views first.

Regards,
Jennie

>>
>> Thank you.
>>
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