>>> Within the data to import most rows have 20 till 50 duplicates.
>>> Sometime much more, sometimes less.
>> In that case (source data has lots of redundancy), after importing the
>> data chunks in parallel, you can run a first pass of de-duplication on
>> the chunks, also in parallel, something like :
>> CREATE TEMP TABLE foo_1_dedup AS SELECT DISTINCT * FROM foo_1;
>> or you could compute some aggregates, counts, etc. Same as before, no
>> WAL needed, and you can use all your cores in parallel.
>> From what you say this should reduce the size of your imported data
>> by a lot (and hence the time spent in the non-parallel operation).
> Thank you very much for this advice. I've tried it inanother project
> with similar import-problems. This really speed the import up.
Glad it was useful ;)