I wonder if it is getting slower because of the date query that you're
doing? You may try indexing raster_date field. Putting an index on that
might slow down inserts but it would improve updates. I would certainly
expect that your updates would get slower overtime for a non-indexed date
match.
Sounds reasonable to me. You could try splitting the process between your 4 or
8 processors, each importing a selection of files. Maybe this could help, maybe
this could make the whole process even slower (depend on what is slow the CPU
or the disk)...
If you don't necessarily need all the