On Fri, Nov 14, 2014 at 02:51:32PM +1300, David Rowley wrote: > Likely for most aggregates, like count, sum, max, min, bit_and and bit_or the > merge function would be the same as the transition function, as the state type > is just the same as the input type. It would only be aggregates like avg(), > stddev*(), bool_and() and bool_or() that would need a new merge function > made... These would be no more complex than the transition functions... Which > are just a few lines of code anyway. > > We'd simply just not run parallel query if any aggregates used in the query > didn't have a merge function. > > When I mentioned this, I didn't mean to appear to be placing a road block.I > was > just bringing to the table the information that COUNT(*) + COUNT(*) works ok > for merging COUNT(*)'s "sub totals", but AVG(n) + AVG(n) does not.
Sorry, late reply, but, FYI, I don't think our percentile functions can't be parallelized in the same way: test=> \daS *percent* List of aggregate functions Schema | Name | Result data type | Argument data types | Description ------------+-----------------+--------------------+----------------------------------------------+------------------------------------- pg_catalog | percent_rank | double precision | VARIADIC "any" ORDER BY VARIADIC "any" | fractional rank of hypothetical row pg_catalog | percentile_cont | double precision | double precision ORDER BY double precision | continuous distribution percentile pg_catalog | percentile_cont | double precision[] | double precision[] ORDER BY double precision | multiple continuous percentiles pg_catalog | percentile_cont | interval | double precision ORDER BY interval | continuous distribution percentile pg_catalog | percentile_cont | interval[] | double precision[] ORDER BY interval | multiple continuous percentiles pg_catalog | percentile_disc | anyelement | double precision ORDER BY anyelement | discrete percentile pg_catalog | percentile_disc | anyarray | double precision[] ORDER BY anyelement | multiple discrete percentiles -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + Everyone has their own god. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers