Re: [HACKERS] GSOC'17 project introduction: Parallel COPY executionwith errors handling

On 9 Jun 2017, at 01:09, Peter Geoghegan <pg@bowt.ie> wrote:

Adding a full support of ON CONFLICT DO NOTHING/UPDATE to COPY seems
to be a large separated task and is out of the current project scope, but
maybe there is
a relatively simple way to somehow perform internally tuples insert with
ON CONFLICT DO NOTHING? I have added Peter Geoghegan to cc, as
I understand he is the major contributor of UPSERT in PostgreSQL. It would
be great
if he will answer this question.

I think that there is a way of making COPY use "speculative
insertion", so that it behaves the same as ON CONFLICT DO NOTHING with
no inference specification. Whether or not this is useful depends on a
lot of things.

I think that you need to more formally identify what errors your new
COPY error handling will need to swallow.

...

My advice right now is: see if you can figure out a way of doing what
you want without subtransactions at all, possibly by cutting some
scope. For example, maybe it would be satisfactory to have the
implementation just ignore constraint violations, but still raise
errors for invalid input for types.

Is there really much value in ignoring errors due to invalid encoding?