Refactor CopyFrom() in copyfrom.c.

This commit simplifies CopyFrom() by removing the unnecessary local variable
'skipped', which tracked the number of rows skipped due to on_error = 'ignore'.
That count is already handled by cstate->num_errors, so the 'skipped' variable
was redundant.

Additionally, the condition on_error != COPY_ON_ERROR_STOP is removed.
Since on_error == COPY_ON_ERROR_IGNORE is already checked, and on_error
only has two values (ignore and stop), the additional check was redundant
and made the logic harder to read. Seemingly this was introduced
in preparation for a future patch, but the current checks don’t offer
clear value and have been removed to improve readability.

Author: Atsushi Torikoshi
Reviewed-by: Masahiko Sawada, Fujii Masao
Discussion: https://postgr.es/m/ab59dad10490ea3734cf022b16c24cfd@oss.nttdata.com

src/backend/commands/copyfrom.c

@@ -657,7 +657,6 @@ CopyFrom(CopyFromState cstate)
 	CopyMultiInsertInfo multiInsertInfo = {0};	/* pacify compiler */
 	int64		processed = 0;
 	int64		excluded = 0;
-	int64		skipped = 0;
 	bool		has_before_insert_row_trig;
 	bool		has_instead_insert_row_trig;
 	bool		leafpart_use_multi_insert = false;
@@ -1004,26 +1003,22 @@ CopyFrom(CopyFromState cstate)
 		if (!NextCopyFrom(cstate, econtext, myslot->tts_values, myslot->tts_isnull))
 			break;
 
-		if (cstate->opts.on_error != COPY_ON_ERROR_STOP &&
+		if (cstate->opts.on_error == COPY_ON_ERROR_IGNORE &&
 			cstate->escontext->error_occurred)
 		{
 			/*
-			 * Soft error occurred, skip this tuple and deal with error
-			 * information according to ON_ERROR.
+			 * Soft error occurred, skip this tuple and just make
+			 * ErrorSaveContext ready for the next NextCopyFrom. Since we
+			 * don't set details_wanted and error_data is not to be filled,
+			 * just resetting error_occurred is enough.
 			 */
-			if (cstate->opts.on_error == COPY_ON_ERROR_IGNORE)
-
-				/*
-				 * Just make ErrorSaveContext ready for the next NextCopyFrom.
-				 * Since we don't set details_wanted and error_data is not to
-				 * be filled, just resetting error_occurred is enough.
-				 */
-				cstate->escontext->error_occurred = false;
+			cstate->escontext->error_occurred = false;
 
 			/* Report that this tuple was skipped by the ON_ERROR clause */
 			pgstat_progress_update_param(PROGRESS_COPY_TUPLES_SKIPPED,
-										 ++skipped);
+										 cstate->num_errors);
 
+			/* Repeat NextCopyFrom() until no soft error occurs */
 			continue;
 		}