Fix crash in multi-insert COPY

A bug introduced in 0d5f05cde0
considered the *previous* partition's triggers when deciding whether
multi-insert can be used.  Rearrange the code so that the current
partition is considered.

Author: Ashutosh Sharma <ashu.coek88@gmail.com>

src/backend/commands/copy.c

@@ -2783,21 +2783,7 @@ CopyFrom(CopyState cstate)
 						lastPartitionSampleLineNo = cstate->cur_lineno;
 						nPartitionChanges = 0;
 					}
-
-					/*
-					 * Tests have shown that using multi-inserts when the
-					 * partition changes on every tuple slightly decreases the
-					 * performance, however, there are benefits even when only
-					 * some batches have just 2 tuples, so let's enable
-					 * multi-inserts even when the average is quite low.
-					 */
-					leafpart_use_multi_insert = avgTuplesPerPartChange >= 1.3 &&
-						!has_before_insert_row_trig &&
-						!has_instead_insert_row_trig &&
-						resultRelInfo->ri_FdwRoutine == NULL;
 				}
-				else
-					leafpart_use_multi_insert = false;
 
 				/*
 				 * Overwrite resultRelInfo with the corresponding partition's
@@ -2821,6 +2807,19 @@ CopyFrom(CopyState cstate)
 				has_instead_insert_row_trig = (resultRelInfo->ri_TrigDesc &&
 											   resultRelInfo->ri_TrigDesc->trig_insert_instead_row);
 
+				/*
+				 * Tests have shown that using multi-inserts when the
+				 * partition changes on every tuple slightly decreases the
+				 * performance, however, there are benefits even when only
+				 * some batches have just 2 tuples, so let's enable
+				 * multi-inserts even when the average is quite low.
+				 */
+				leafpart_use_multi_insert = insertMethod == CIM_MULTI_CONDITIONAL &&
+					avgTuplesPerPartChange >= 1.3 &&
+					!has_before_insert_row_trig &&
+					!has_instead_insert_row_trig &&
+					resultRelInfo->ri_FdwRoutine == NULL;
+
 				/*
 				 * We'd better make the bulk insert mechanism gets a new
 				 * buffer when the partition being inserted into changes.

src/test/regress/input/copy.source

@@ -162,4 +162,23 @@ copy parted_copytest from '@abs_builddir@/results/parted_copytest.csv';
 select tableoid::regclass,count(*),sum(a) from parted_copytest
 group by tableoid order by tableoid::regclass::name;
 
+truncate parted_copytest;
+
+-- create before insert row trigger on parted_copytest_a2
+create function part_ins_func() returns trigger language plpgsql as $$
+begin
+  return new;
+end;
+$$;
+
+create trigger part_ins_trig
+	before insert on parted_copytest_a2
+	for each row
+	execute procedure part_ins_func();
+
+copy parted_copytest from '@abs_builddir@/results/parted_copytest.csv';
+
+select tableoid::regclass,count(*),sum(a) from parted_copytest
+group by tableoid order by tableoid::regclass::name;
+
 drop table parted_copytest;

src/test/regress/output/copy.source

@@ -121,4 +121,24 @@ group by tableoid order by tableoid::regclass::name;
  parted_copytest_a2 |    10 |  10055
 (2 rows)
 
+truncate parted_copytest;
+-- create before insert row trigger on parted_copytest_a2
+create function part_ins_func() returns trigger language plpgsql as $$
+begin
+  return new;
+end;
+$$;
+create trigger part_ins_trig
+	before insert on parted_copytest_a2
+	for each row
+	execute procedure part_ins_func();
+copy parted_copytest from '@abs_builddir@/results/parted_copytest.csv';
+select tableoid::regclass,count(*),sum(a) from parted_copytest
+group by tableoid order by tableoid::regclass::name;
+      tableoid      | count |  sum   
+--------------------+-------+--------
+ parted_copytest_a1 |  1010 | 510655
+ parted_copytest_a2 |    10 |  10055
+(2 rows)
+
 drop table parted_copytest;