I tried the string_concat function. Looks like it only works with comma.

[d22shen]

I tried to call this function with "-" delimeter, but it looks like comma is still used as part of the separators somehow. I didn't make any change to the udf sample code.

create aggregate function string_concat(string, string) returns string
location '/user/history/libudasample.so'
init_fn='StringConcatInit'
update_fn='StringConcatUpdate'
merge_fn='StringConcatMerge'
finalize_fn='StringConcatFinalize';

My data is as follows:
+----+----------+-----+-----------+--------+
| id | name | age | address | salary |
+----+----------+-----+-----------+--------+
| 7 | Hardik | 22 | MP | 32000 |
| 8 | Komal | 22 | Bhopal | 32000 |
| 9 | Khilan | 25 | Kota | 15000 |
| 12 | Khilan4 | 25 | Kota | 15000 |
| 14 | Khilan6 | 25 | Kota | 15000 |
| 11 | Khilan3 | 25 | Kota | 15000 |
| 15 | Khilan7 | 25 | Kota | 15000 |
| 2 | Khilan | 25 | Delhi | 15000 |
| 13 | Khilan5 | 25 | Kota | 15000 |
| 4 | Chaitali | 25 | Mumbai | 35000 |
| 1 | Ramesh | 32 | Ahmedabad | 20000 |
| 6 | Komal | 22 | MP | 32000 |
| 3 | kaushik | 23 | Kota | 30000 |
| 10 | Khilan2 | 25 | Kota | 15000 |
| 5 | Hardik | 27 | Bhopal | 40000 |
+----+----------+-----+-----------+--------+

select string_concat(name, "-") from employee_kudu group by address;
+----------------------------------------------------------------+
| db_kudu.string_concat(name, '-') |
+----------------------------------------------------------------+
| Chaitali |
| Khilan |
| Khilan5,Khilan,kaushik-Khilan2,Khilan4-Khilan6-Khilan3-Khilan7 |
| Hardik,Komal |
| Ramesh |
| Komal,Hardik |
+----------------------------------------------------------------+

[d22shen]

Weird, github won't display understore "_" but it is there in the edit window.
Changed underscore to "-" but the result is actually the same.

[d22shen]

To complement this issue, I used the sample on Kudu with two nodes. Is it because of the merge issue? The merge calls "StringConcatUpdate(context, src, ",", dst);" that comma is hard-coded and used.

[timarmstrong]

@d22shen yes it looks like the bug is in StringConcatMerge() like you mentioned. I think to fix it the UDA would need to be modified to store the separator in the intermediate value.