Re: on_error table, saving error info to a table

Generally looks good to me, I only found a few typos:

+								errmsg("saving error information to table \"%s\" row due to
data type incompatibility at line %" PRIu64 " for column \"%s\":
\"%s\"",

Is row needed there?

+	 * TODO: Allow cstate->error_rel to be a partitioned table. This should be
+	 * not difficult, but requires proper handling of constraints and triggers

should not be difficult

+        privileges on it. During the error records inseration,
+        <literal>NOT NULL</literal> and <literal>CHECK</literal>
constraints are enforced,
+        and both row-level and statement-level triggers will be fired.

record's insertion

Maybe this could explicitly mention that failure to insert into the
error table will fail the copy statement? Or some better wording of
that, as it is allowed behavior with triggers.