Hi I'm trying to write an aggrecate collect_distinct(int8) which puts all distinct values into an array. My first try was defining an aggregate "collect" using array_append, and doing "select collect(distinct <field>) ..", but this is quite slow - probably because distinct sorts the values, instead of using a hash to filter out duplicates. Using perl, and a perl-hash was even slower, so I wrote my to c-functions (actualy c++), which use a STL hash_set to filter out duplicates. I initially defined my state-transaction function as "collect_distinct(internal, int8) returns internal". The parameter marked internal was a pointer to a STL hash_set. But using this to define an aggregate failed, because internal seems to be forbidden as a state-type. I now resorted to a crude hack to get this running - I changed "internal" to "int4", and just cast my pointer to a int4 before returning it, and after receiving it as an argument. This at least enabled me to do some benchmarking, and performance-wise things look good... Before using this on a production system, I need to get rid of that hack, but I don't see how this could be done ATM... Maybe someone here could give me a hint how this could work... greetings, Florian Pflug
