2011/4/27 Adrian Schreyer <ams...@cam.ac.uk>: > The largest arrays I expect at the moment are more or less sparse > vectors of around 4.8k elements and I have noticed that the > input/output (C/C++ extension) does not scale well with the number of > elements in the array. > > Using a function that sums all elements in the array, this is the time > it takes for ~150k arrays of various sizes (including ordering desc > and limit 10): >
PostgreSQL doesn't use a index for access to array fields. So access to fields of packed arrays can be slower for higher subscripts. Regards Pavel Stehule > 128: 61ms > 256: 80ms > 512: 681ms > 1024 1065ms > 2048 7682ms > 4096 21332ms > > That's why I thought that the construction of the PostgreSQL array was > not optimal. > > On Wed, Apr 27, 2011 at 14:49, Merlin Moncure <mmonc...@gmail.com> wrote: >> On Wed, Apr 27, 2011 at 6:02 AM, Adrian Schreyer <ams...@cam.ac.uk> wrote: >>> At the moment I am using the following code to construct a PostgreSQL >>> array from a C array in my C extension but I am not so sure if this is >>> really the best solution: >>> >>> const int *data = array.data(); // C array >>> Datum *d = (Datum *) palloc(sizeof(Datum) * size); >>> >>> for (int i = 0; i < size; i++) d[i] = Int32GetDatum(data[i]); >>> >>> ArrayType *a = construct_array(d, size, INT4OID, sizeof(int4), true, 'i'); >>> >>> Is this okay or is there a better solution (existing function in the >>> PostgreSQL source for example)? >> >> That's pretty much the best way AFAIK. Int32GetDatum doesn't do >> anything fancy -- it's just a 32 bit mask/assignment. constructing >> the array at once is going to be a lot better than incrementally >> creating it. Do you expect the arrays to be large, say bigger than >> 10k elements? >> >> merlin >> > > -- > Sent via pgsql-general mailing list (pgsql-general@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-general > -- Sent via pgsql-general mailing list (pgsql-general@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
