Re: POC: postgres_fdw insert batching

>I didn't get this. We are executing an INSERT on the foreign server,
>so we get the number of rows INSERTed from that server. We should just
>add those up across batches. If there's a failure, it would abort the
>transaction, local as well as remote.
>

True, but it's not the FDW code doing the counting - it's the caller,
depending on whether the ExecForeignInsert returns a valid slot or NULL.
So it's not quite possible to just return a number of inserted tuples,
as returned by the remote server.

>In your patch, I see that an INSERT statement with batch is
>constructed as INSERT INTO ... VALUES (...), (...) as many values as
>the batch size. That won't work as is for UPDATE/DELETE since we can't
>pass multiple pairs of ctids and columns to be updated for each ctid
>in one statement. Maybe we could build as many UPDATE/DELETE
>statements as the size of a batch, but that would be ugly. What we
>need is a feature like a batch prepared statement in libpq similar to
>what JDBC supports
>((https://mkyong.com/jdbc/jdbc-preparedstatement-example-batch-update/).
>This will allow a single prepared statement to be executed with a
>batch of parameters, each batch corresponding to one foreign DML
>statement.
>

I'm pretty sure we could make it work with some array/unnest tricks to
build a relation, and use that as a source of data.

I don't see why not support both, the use cases are somewhat different I
think.