[HACKERS] Stats for triggers on partitioned tables not shown in EXPLAIN ANALYZE

Hi hackers,

I noticed that runtime stats for BEFORE ROW INSERT triggers on leaf 
partitions of partitioned tables aren't reported in EXPLAIN ANALYZE. 
Here is an example:

postgres=# create table trigger_test (a int, b text) partition by list (a);
CREATE TABLE
postgres=# create table trigger_test1 partition of trigger_test for 
values in (1);
CREATE TABLE
postgres=# create trigger before_ins_row_trig BEFORE INSERT ON 
trigger_test1 FOR EACH ROW EXECUTE PROCEDURE trigger_data();
CREATE TRIGGER
postgres=# create trigger after_ins_row_trig AFTER INSERT ON 
trigger_test1 FOR EACH ROW EXECUTE PROCEDURE trigger_data();
CREATE TRIGGER
postgres=# explain analyze insert into trigger_test values (1, 'foo');
NOTICE:  before_ins_row_trig() BEFORE ROW INSERT ON trigger_test1
NOTICE:  NEW: (1,foo)
NOTICE:  after_ins_row_trig() AFTER ROW INSERT ON trigger_test1
NOTICE:  NEW: (1,foo)
                                              QUERY PLAN
-----------------------------------------------------------------------------------------------------
  Insert on trigger_test  (cost=0.00..0.01 rows=1 width=36) (actual 
time=0.193..0.193 rows=0 loops=1)
    ->  Result  (cost=0.00..0.01 rows=1 width=36) (actual 
time=0.002..0.003 rows=1 loops=1)
  Planning time: 0.027 ms
  Trigger after_ins_row_trig on trigger_test1: time=0.075 calls=1
  Execution time: 0.310 ms
(5 rows)

where trig_data() is borrowed from the regression test in postgres_fdw. 
The stats for the AFTER ROW INSERT trigger after_ins_row_trig are well 
shown in the output, but the stats for the BEFORE ROW INSERT trigger 
before_ins_row_trig aren't at all.  I think we should show the latter as 
well.

Another thing I noticed is: runtime stats for BEFORE STATEMENT 
UPDATE/DELETE triggers on partitioned table roots aren't reported in 
EXPLAIN ANALYZE, either, as shown in a below example:

postgres=# create trigger before_upd_stmt_trig BEFORE UPDATE ON 
trigger_test FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
CREATE TRIGGER
postgres=# create trigger after_upd_stmt_trig AFTER UPDATE ON 
trigger_test FOR EACH STATEMENT EXECUTE PROCEDURE trigger_func();
CREATE TRIGGER
postgres=# explain analyze update trigger_test set b = 'bar' where a = 1;
NOTICE:  trigger_func(<NULL>) called: action = UPDATE, when = BEFORE, 
level = STATEMENT
NOTICE:  trigger_func(<NULL>) called: action = UPDATE, when = AFTER, 
level = STATEMENT
                                                   QUERY PLAN

----------------------------------------------------------------------------------------------------------
-----
  Update on trigger_test  (cost=0.00..25.88 rows=6 width=42) (actual 
time=0.296..0.296 rows=0 loops=1)
    Update on trigger_test1
    ->  Seq Scan on trigger_test1  (cost=0.00..25.88 rows=6 width=42) 
(actual time=0.010..0.011 rows=1 loops=1)
          Filter: (a = 1)
  Planning time: 0.152 ms
  Trigger after_upd_stmt_trig on trigger_test: time=0.141 calls=1
  Execution time: 0.476 ms
(7 rows)

where trigger_func() is borrowed from the regression test, too.  The 
stats for the BEFORE STATEMENT UPDATE trigger before_upd_stmt_trig 
aren't shown at all in the output.  I think this should also be fixed. 
So here is a patch for fixing both issues.  Changes I made are:

* To fix the former, I added a new List member es_leaf_result_relations 
to EState, modified ExecSetupPartitionTupleRouting so that it creates 
ResultRelInfos with the EState's es_instrument and then saves them in 
that list, and modified ExplainPrintTriggers to show stats for BEFORE 
ROW INSERT triggers on leaf partitions (if any) by looking at that list. 
  I also modified copy.c so that ExecSetupPartitionTupleRouting and 
related things are performed in CopyFrom after its EState creation.

* To fix the latter, I modified ExplainPrintTriggers to show stats for 
BEFORE STATEMENT UPDATE/DELETE triggers on partitioned table roots (if 
any) by looking at the es_root_result_relations array.

* While fixing these, I noticed that AFTER ROW INSERT triggers on leaf 
partitions and BEFORE STATEMENT UPDATE/DELETE triggers on partitioned 
table roots re-open relations and re-create ResultRelInfos (trigger-only 
ResultRelInfos!) in ExecGetTriggerResultRel when executing triggers (and 
that in the above examples, the stats for AFTER ROW INSERT trigger/AFTER 
STATEMENT UPDATE trigger are shown the result for 
es_trig_target_relations in ExplainPrintTriggers).  But that wouldn't be 
efficient (and EXPLAIN ANALYZE might produce odd outputs), so I modified 
ExecGetTriggerResultRel so that it searches es_leaf_result_relations and 
es_root_result_relations in addition to es_result_relations.

Best regards,
Etsuro Fujita

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