Subject: Re: Asynchronous MergeAppend

From: Alena Rybakina <[email-masked]>
Date: Sat, 10 Aug 2024 23:24:43 +0300

Hi! Thank you for your work on this subject! I think this is a very 
useful optimization)

While looking through your code, I noticed some points that I think 
should be taken into account. Firstly, I noticed only two tests to 
verify the functionality of this function and I think that this is not 
enough.
Are you thinking about adding some tests with queries involving, for 
example, join connections with different tables and unusual operators?

In addition, I have a question about testing your feature on a 
benchmark. Are you going to do this?

On 17.07.2024 16:24, Alexander Pyhalov wrote:
> Hello.
>
> I'd like to make MergeAppend node Async-capable like Append node. 
> Nowadays when planner chooses MergeAppend plan, asynchronous execution 
> is not possible. With attached patches you can see plans like
>
> EXPLAIN (VERBOSE, COSTS OFF)
> SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
>                                                           QUERY PLAN
> ------------------------------------------------------------------------------------------------------------------------------ 
>
>  Merge Append
>    Sort Key: async_pt.b, async_pt.a
>    ->  Async Foreign Scan on public.async_p1 async_pt_1
>          Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
>          Remote SQL: SELECT a, b, c FROM public.base_tbl1 WHERE (((b % 
> 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
>    ->  Async Foreign Scan on public.async_p2 async_pt_2
>          Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
>          Remote SQL: SELECT a, b, c FROM public.base_tbl2 WHERE (((b % 
> 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
>
> This can be quite profitable (in our test cases you can gain up to two 
> times better speed with MergeAppend async execution on remote servers).
>
> Code for asynchronous execution in Merge Append was mostly borrowed 
> from Append node.
>
> What significantly differs - in ExecMergeAppendAsyncGetNext() you must 
> return tuple from the specified slot.
> Subplan number determines tuple slot where data should be retrieved 
> to. When subplan is ready to provide some data,
> it's cached in ms_asyncresults. When we get tuple for subplan, 
> specified in ExecMergeAppendAsyncGetNext(),
> ExecMergeAppendAsyncRequest() returns true and loop in 
> ExecMergeAppendAsyncGetNext() ends. We can fetch data for
> subplans which either don't have cached result ready or have already 
> returned them to the upper node. This
> flag is stored in ms_has_asyncresults. As we can get data for some 
> subplan either earlier or after loop in ExecMergeAppendAsyncRequest(),
> we check this flag twice in this function.
> Unlike ExecAppendAsyncEventWait(), it seems 
> ExecMergeAppendAsyncEventWait() doesn't need a timeout - as there's no 
> need to get result
> from synchronous subplan if a tuple form async one was explicitly 
> requested.
>
> Also we had to fix postgres_fdw to avoid directly looking at Append 
> fields. Perhaps, accesors to Append fields look strange, but allows
> to avoid some code duplication. I suppose, duplication could be even 
> less if we reworked async Append implementation, but so far I haven't
> tried to do this to avoid big diff from master.
>
> Also mark_async_capable() believes that path corresponds to plan. This 
> can be not true when create_[merge_]append_plan() inserts sort node.
> In this case mark_async_capable() can treat Sort plan node as some 
> other and crash, so there's a small fix for this.

I think you should add this explanation to the commit message because 
without it it's hard to understand the full picture of how your code works.

-- 
Regards,
Alena Rybakina
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 20 Aug 2024 12:14:44 +0300

Hi.

> example, join connections with different tables and unusual operators?

I've added some more tests - tests for joins and pruning.

> benchmark. Are you going to do this?

The main reason for this work is a dramatic performance degradation when 
Append plans with async foreign scan nodes are switched to MergeAppend 
plans with synchronous foreign scans.

I've performed some synthetic tests to prove the benefits of async Merge 
Append. So far tests are performed on one physical host.

For tests I've deployed 3 PostgreSQL instances on ports 5432-5434.

The first instance:
create server s2 foreign data wrapper postgres_fdw OPTIONS ( port 
'5433', dbname 'postgres', async_capable 'on');
create server s3 foreign data wrapper postgres_fdw OPTIONS ( port 
'5434', dbname 'postgres', async_capable 'on');

create foreign table players_p1 partition of players for values with 
(modulus 4, remainder 0) server s2;
create foreign table players_p2 partition of players for values with 
(modulus 4, remainder 1) server s2;
create foreign table players_p3 partition of players for values with 
(modulus 4, remainder 2) server s3;
create foreign table players_p4 partition of players for values with 
(modulus 4, remainder 3) server s3;

s2 instance:
create table players_p1  (id int, name text, score int);
create table players_p2  (id int, name text, score int);
create index on players_p1(score);
create index on players_p2(score);

s3 instance:
create table players_p3  (id int, name text, score int);
create table players_p4  (id int, name text, score int);
create index on players_p3(score);
create index on players_p4(score);

s1 instance:
insert into players select i, 'player_' ||i, random()* 100 from 
generate_series(1,100000) i;

pgbench script:
\set rnd_offset random(0,200)
\set rnd_limit  random(10,20)

select * from players order by score desc offset :rnd_offset limit 
:rnd_limit;

pgbench was run as:
pgbench -n -f 1.sql  postgres -T 100 -c 16 -j 16

CPU idle was about 5-10%.

pgbench results:

Without patch, async_capable on:

pgbench (14.13, server 18devel)
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 16
number of threads: 16
duration: 100 s
number of transactions actually processed: 130523
latency average = 12.257 ms
initial connection time = 29.824 ms
tps = 1305.363500 (without initial connection time)

Without patch, async_capable off:

pgbench (14.13, server 18devel)
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 16
number of threads: 16
duration: 100 s
number of transactions actually processed: 130075
latency average = 12.299 ms
initial connection time = 26.931 ms
tps = 1300.877993 (without initial connection time)

as expected - we see no difference.

Patched, async_capable on:

pgbench (14.13, server 18devel)
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 16
number of threads: 16
duration: 100 s
number of transactions actually processed: 135616
latency average = 11.796 ms
initial connection time = 28.619 ms
tps = 1356.341587 (without initial connection time)

Patched, async_capable off:

pgbench (14.13, server 18devel)
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 16
number of threads: 16
duration: 100 s
number of transactions actually processed: 131300
latency average = 12.185 ms
initial connection time = 29.573 ms
tps = 1313.138405 (without initial connection time)

Here we can see that async MergeAppend behaves a bit better. You can 
argue that benefit is not so big and perhaps is related to some random 
factors.
However, if we set number of threads to 1, so that CPU has idle cores, 
we'll see more evident improvements:

Patched, async_capable on:
pgbench (14.13, server 18devel)
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 1
number of threads: 1
duration: 100 s
number of transactions actually processed: 20221
latency average = 4.945 ms
initial connection time = 7.035 ms
tps = 202.221816 (without initial connection time)

Patched, async_capable off
transaction type: 1.sql
scaling factor: 1
query mode: simple
number of clients: 1
number of threads: 1
duration: 100 s
number of transactions actually processed: 14941
latency average = 6.693 ms
initial connection time = 7.037 ms
tps = 149.415688 (without initial connection time)

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From 67477ab452dfc57aa9e47e4462c9f87b66911951 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Wed, 19 Jul 2023 15:42:24 +0300
Subject: [PATCH 2/2] MergeAppend should support Async Foreign Scan subplans

---
 .../postgres_fdw/expected/postgres_fdw.out    | 247 ++++++++++
 contrib/postgres_fdw/postgres_fdw.c           |  10 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     |  78 +++
 doc/src/sgml/config.sgml                      |  14 +
 src/backend/executor/execAsync.c              |   4 +
 src/backend/executor/nodeMergeAppend.c        | 458 +++++++++++++++++-
 src/backend/optimizer/path/costsize.c         |   1 +
 src/backend/optimizer/plan/createplan.c       |   8 +
 src/backend/utils/misc/guc_tables.c           |  10 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/executor/nodeMergeAppend.h        |   1 +
 src/include/nodes/execnodes.h                 |  56 +++
 src/include/optimizer/cost.h                  |   1 +
 src/test/regress/expected/sysviews.out        |   3 +-
 14 files changed, 886 insertions(+), 6 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index f3eb055e2c7..3aba5a877af 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11194,6 +11194,46 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+                                                          QUERY PLAN                                                          
+------------------------------------------------------------------------------------------------------------------------------
+ Merge Append
+   Sort Key: async_pt.b, async_pt.a
+   ->  Async Foreign Scan on public.async_p1 async_pt_1
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         Remote SQL: SELECT a, b, c FROM public.base_tbl1 WHERE (((b % 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p2 async_pt_2
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         Remote SQL: SELECT a, b, c FROM public.base_tbl2 WHERE (((b % 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+(8 rows)
+
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+  a   |  b  |  c   
+------+-----+------
+ 1000 |   0 | 0000
+ 2000 |   0 | 0000
+ 1100 | 100 | 0100
+ 2100 | 100 | 0100
+ 1200 | 200 | 0200
+ 2200 | 200 | 0200
+ 1300 | 300 | 0300
+ 2300 | 300 | 0300
+ 1400 | 400 | 0400
+ 2400 | 400 | 0400
+ 1500 | 500 | 0500
+ 2500 | 500 | 0500
+ 1600 | 600 | 0600
+ 2600 | 600 | 0600
+ 1700 | 700 | 0700
+ 2700 | 700 | 0700
+ 1800 | 800 | 0800
+ 2800 | 800 | 0800
+ 1900 | 900 | 0900
+ 2900 | 900 | 0900
+(20 rows)
+
 -- Test error handling, if accessing one of the foreign partitions errors out
 CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
   SERVER loopback OPTIONS (table_name 'non_existent_table');
@@ -11237,6 +11277,35 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+                                              QUERY PLAN                                              
+------------------------------------------------------------------------------------------------------
+ Merge Append
+   Sort Key: async_pt.b, async_pt.a
+   ->  Async Foreign Scan on public.async_p1 async_pt_1
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         Filter: (async_pt_1.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl1 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p2 async_pt_2
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         Filter: (async_pt_2.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl2 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p3 async_pt_3
+         Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+         Filter: (async_pt_3.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl3 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+(14 rows)
+
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+  a   |  b  |  c   
+------+-----+------
+ 1505 | 505 | 0505
+ 2505 | 505 | 0505
+ 3505 | 505 | 0505
+(3 rows)
+
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 -- Check case where the partitioned table has local/remote partitions
@@ -11272,6 +11341,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+                                              QUERY PLAN                                              
+------------------------------------------------------------------------------------------------------
+ Merge Append
+   Sort Key: async_pt.b, async_pt.a
+   ->  Async Foreign Scan on public.async_p1 async_pt_1
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         Filter: (async_pt_1.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl1 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p2 async_pt_2
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         Filter: (async_pt_2.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl2 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Sort
+         Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+         Sort Key: async_pt_3.b, async_pt_3.a
+         ->  Seq Scan on public.async_p3 async_pt_3
+               Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+               Filter: (async_pt_3.b === 505)
+(16 rows)
+
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+  a   |  b  |  c   
+------+-----+------
+ 1505 | 505 | 0505
+ 2505 | 505 | 0505
+ 3505 | 505 | 0505
+(3 rows)
+
 -- partitionwise joins
 SET enable_partitionwise_join TO true;
 CREATE TABLE join_tbl (a1 int, b1 int, c1 text, a2 int, b2 int, c2 text);
@@ -12054,6 +12154,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 NOTICE:  drop cascades to foreign table foreign_tbl2
 DROP TABLE base_tbl;
+-- Test async Merge Append
+CREATE TABLE distr1 (i int, j int, k text) PARTITION BY HASH (i);
+CREATE TABLE base1 (i int, j int, k text);
+CREATE TABLE base2 (i int, j int, k text);
+CREATE FOREIGN TABLE distr1_p1 PARTITION OF distr1 FOR VALUES WITH (MODULUS 2, REMAINDER 0)
+SERVER loopback OPTIONS (table_name 'base1');
+CREATE FOREIGN TABLE distr1_p2 PARTITION OF distr1 FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+SERVER loopback OPTIONS (table_name 'base2');
+CREATE TABLE distr2 (i int, j int, k text) PARTITION BY HASH (i);
+CREATE TABLE base3 (i int, j int, k text);
+CREATE TABLE base4 (i int, j int, k text);
+CREATE FOREIGN TABLE distr2_p1 PARTITION OF distr2 FOR VALUES WITH (MODULUS 2, REMAINDER 0)
+SERVER loopback OPTIONS (table_name 'base3');
+CREATE FOREIGN TABLE distr2_p2 PARTITION OF distr2 FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+SERVER loopback OPTIONS (table_name 'base4');
+INSERT INTO distr1
+SELECT i, i*10, 'data_' || i FROM generate_series(1, 1000) i;
+INSERT INTO distr2
+SELECT i, i*10, 'data_' || i FROM generate_series(1, 100) i;
+ANALYZE distr1_p1;
+ANALYZE distr1_p2;
+ANALYZE distr2_p1;
+ANALYZE distr2_p2;
+SET enable_partitionwise_join TO ON;
+-- Test joins with async Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM distr1, distr2 WHERE distr1.i=distr2.i AND distr2.j > 90 and distr2.k like 'data%'
+ORDER BY distr2.i LIMIT 10;
+                                                                                                    QUERY PLAN                                                                                                     
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: distr1.i, distr1.j, distr1.k, distr2.i, distr2.j, distr2.k
+   ->  Merge Append
+         Sort Key: distr1.i
+         ->  Async Foreign Scan
+               Output: distr1_1.i, distr1_1.j, distr1_1.k, distr2_1.i, distr2_1.j, distr2_1.k
+               Relations: (public.distr1_p1 distr1_1) INNER JOIN (public.distr2_p1 distr2_1)
+               Remote SQL: SELECT r3.i, r3.j, r3.k, r5.i, r5.j, r5.k FROM (public.base1 r3 INNER JOIN public.base3 r5 ON (((r3.i = r5.i)) AND ((r5.j > 90)) AND ((r5.k ~~ 'data%')))) ORDER BY r3.i ASC NULLS LAST
+         ->  Async Foreign Scan
+               Output: distr1_2.i, distr1_2.j, distr1_2.k, distr2_2.i, distr2_2.j, distr2_2.k
+               Relations: (public.distr1_p2 distr1_2) INNER JOIN (public.distr2_p2 distr2_2)
+               Remote SQL: SELECT r4.i, r4.j, r4.k, r6.i, r6.j, r6.k FROM (public.base2 r4 INNER JOIN public.base4 r6 ON (((r4.i = r6.i)) AND ((r6.j > 90)) AND ((r6.k ~~ 'data%')))) ORDER BY r4.i ASC NULLS LAST
+(12 rows)
+
+SELECT * FROM distr1, distr2 WHERE distr1.i=distr2.i AND distr2.j > 90 and distr2.k like 'data%'
+ORDER BY distr2.i LIMIT 10;
+ i  |  j  |    k    | i  |  j  |    k    
+----+-----+---------+----+-----+---------
+ 10 | 100 | data_10 | 10 | 100 | data_10
+ 11 | 110 | data_11 | 11 | 110 | data_11
+ 12 | 120 | data_12 | 12 | 120 | data_12
+ 13 | 130 | data_13 | 13 | 130 | data_13
+ 14 | 140 | data_14 | 14 | 140 | data_14
+ 15 | 150 | data_15 | 15 | 150 | data_15
+ 16 | 160 | data_16 | 16 | 160 | data_16
+ 17 | 170 | data_17 | 17 | 170 | data_17
+ 18 | 180 | data_18 | 18 | 180 | data_18
+ 19 | 190 | data_19 | 19 | 190 | data_19
+(10 rows)
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM distr1 LEFT JOIN distr2 ON distr1.i=distr2.i AND distr2.k like 'data%' WHERE  distr1.i > 90
+ORDER BY distr1.i LIMIT 20;
+                                                                                                     QUERY PLAN                                                                                                     
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: distr1.i, distr1.j, distr1.k, distr2.i, distr2.j, distr2.k
+   ->  Merge Append
+         Sort Key: distr1.i
+         ->  Async Foreign Scan
+               Output: distr1_1.i, distr1_1.j, distr1_1.k, distr2_1.i, distr2_1.j, distr2_1.k
+               Relations: (public.distr1_p1 distr1_1) LEFT JOIN (public.distr2_p1 distr2_1)
+               Remote SQL: SELECT r4.i, r4.j, r4.k, r6.i, r6.j, r6.k FROM (public.base1 r4 LEFT JOIN public.base3 r6 ON (((r4.i = r6.i)) AND ((r6.k ~~ 'data%')))) WHERE ((r4.i > 90)) ORDER BY r4.i ASC NULLS LAST
+         ->  Async Foreign Scan
+               Output: distr1_2.i, distr1_2.j, distr1_2.k, distr2_2.i, distr2_2.j, distr2_2.k
+               Relations: (public.distr1_p2 distr1_2) LEFT JOIN (public.distr2_p2 distr2_2)
+               Remote SQL: SELECT r5.i, r5.j, r5.k, r7.i, r7.j, r7.k FROM (public.base2 r5 LEFT JOIN public.base4 r7 ON (((r5.i = r7.i)) AND ((r7.k ~~ 'data%')))) WHERE ((r5.i > 90)) ORDER BY r5.i ASC NULLS LAST
+(12 rows)
+
+SELECT * FROM distr1 LEFT JOIN distr2 ON  distr1.i=distr2.i AND distr2.k like 'data%' WHERE distr1.i > 90
+ORDER BY distr1.i LIMIT 20;
+  i  |  j   |    k     |  i  |  j   |    k     
+-----+------+----------+-----+------+----------
+  91 |  910 | data_91  |  91 |  910 | data_91
+  92 |  920 | data_92  |  92 |  920 | data_92
+  93 |  930 | data_93  |  93 |  930 | data_93
+  94 |  940 | data_94  |  94 |  940 | data_94
+  95 |  950 | data_95  |  95 |  950 | data_95
+  96 |  960 | data_96  |  96 |  960 | data_96
+  97 |  970 | data_97  |  97 |  970 | data_97
+  98 |  980 | data_98  |  98 |  980 | data_98
+  99 |  990 | data_99  |  99 |  990 | data_99
+ 100 | 1000 | data_100 | 100 | 1000 | data_100
+ 101 | 1010 | data_101 |     |      | 
+ 102 | 1020 | data_102 |     |      | 
+ 103 | 1030 | data_103 |     |      | 
+ 104 | 1040 | data_104 |     |      | 
+ 105 | 1050 | data_105 |     |      | 
+ 106 | 1060 | data_106 |     |      | 
+ 107 | 1070 | data_107 |     |      | 
+ 108 | 1080 | data_108 |     |      | 
+ 109 | 1090 | data_109 |     |      | 
+ 110 | 1100 | data_110 |     |      | 
+(20 rows)
+
+-- Test pruning with async Merge Append
+DELETE FROM distr2;
+INSERT INTO distr2
+SELECT i%10, i*10, 'data_' || i FROM generate_series(1, 1000) i;
+DEALLOCATE ALL;
+SET plan_cache_mode TO force_generic_plan;
+PREPARE async_pt_query (int, int) AS
+  SELECT * FROM distr2 WHERE i = ANY(ARRAY[$1, $2])
+  ORDER BY i,j
+  LIMIT 10;
+EXPLAIN (VERBOSE, COSTS OFF)
+	EXECUTE async_pt_query(1, 1);
+                                                                         QUERY PLAN                                                                         
+------------------------------------------------------------------------------------------------------------------------------------------------------------
+ Limit
+   Output: distr2.i, distr2.j, distr2.k
+   ->  Merge Append
+         Sort Key: distr2.i, distr2.j
+         Subplans Removed: 1
+         ->  Async Foreign Scan on public.distr2_p1 distr2_1
+               Output: distr2_1.i, distr2_1.j, distr2_1.k
+               Remote SQL: SELECT i, j, k FROM public.base3 WHERE ((i = ANY (ARRAY[$1::integer, $2::integer]))) ORDER BY i ASC NULLS LAST, j ASC NULLS LAST
+(8 rows)
+
+EXECUTE async_pt_query(1, 1);
+ i |  j  |    k    
+---+-----+---------
+ 1 |  10 | data_1
+ 1 | 110 | data_11
+ 1 | 210 | data_21
+ 1 | 310 | data_31
+ 1 | 410 | data_41
+ 1 | 510 | data_51
+ 1 | 610 | data_61
+ 1 | 710 | data_71
+ 1 | 810 | data_81
+ 1 | 910 | data_91
+(10 rows)
+
+RESET plan_cache_mode;
+RESET enable_partitionwise_join;
+DROP TABLE distr1, distr2, base1, base2, base3, base4;
 ALTER SERVER loopback OPTIONS (DROP async_capable);
 ALTER SERVER loopback2 OPTIONS (DROP async_capable);
 -- ===================================================================
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index fc65d81e217..13093190d45 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -7262,12 +7262,16 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)
 	ForeignScanState *node = (ForeignScanState *) areq->requestee;
 	PgFdwScanState *fsstate = (PgFdwScanState *) node->fdw_state;
 	AsyncRequest *pendingAreq = fsstate->conn_state->pendingAreq;
-	AppendState *requestor = (AppendState *) areq->requestor;
-	WaitEventSet *set = requestor->as_eventset;
+	PlanState  *requestor = areq->requestor;
+	WaitEventSet *set;
+	Bitmapset  *needrequest;
 
 	/* This should not be called unless callback_pending */
 	Assert(areq->callback_pending);
 
+	set = GetAppendEventSet(requestor);
+	needrequest = GetNeedRequest(requestor);
+
 	/*
 	 * If process_pending_request() has been invoked on the given request
 	 * before we get here, we might have some tuples already; in which case
@@ -7305,7 +7309,7 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)
 		 * below, because we might otherwise end up with no configured events
 		 * other than the postmaster death event.
 		 */
-		if (!bms_is_empty(requestor->as_needrequest))
+		if (!bms_is_empty(needrequest))
 			return;
 		if (GetNumRegisteredWaitEvents(set) > 1)
 			return;
diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index 0734716ad90..d90978e8bfc 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -3789,6 +3789,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+
 -- Test error handling, if accessing one of the foreign partitions errors out
 CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
   SERVER loopback OPTIONS (table_name 'non_existent_table');
@@ -3809,6 +3814,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 
@@ -3824,6 +3834,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+
 -- partitionwise joins
 SET enable_partitionwise_join TO true;
 
@@ -4062,6 +4077,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;
 
+-- Test async Merge Append
+CREATE TABLE distr1 (i int, j int, k text) PARTITION BY HASH (i);
+CREATE TABLE base1 (i int, j int, k text);
+CREATE TABLE base2 (i int, j int, k text);
+CREATE FOREIGN TABLE distr1_p1 PARTITION OF distr1 FOR VALUES WITH (MODULUS 2, REMAINDER 0)
+SERVER loopback OPTIONS (table_name 'base1');
+CREATE FOREIGN TABLE distr1_p2 PARTITION OF distr1 FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+SERVER loopback OPTIONS (table_name 'base2');
+
+CREATE TABLE distr2 (i int, j int, k text) PARTITION BY HASH (i);
+CREATE TABLE base3 (i int, j int, k text);
+CREATE TABLE base4 (i int, j int, k text);
+CREATE FOREIGN TABLE distr2_p1 PARTITION OF distr2 FOR VALUES WITH (MODULUS 2, REMAINDER 0)
+SERVER loopback OPTIONS (table_name 'base3');
+CREATE FOREIGN TABLE distr2_p2 PARTITION OF distr2 FOR VALUES WITH (MODULUS 2, REMAINDER 1)
+SERVER loopback OPTIONS (table_name 'base4');
+
+INSERT INTO distr1
+SELECT i, i*10, 'data_' || i FROM generate_series(1, 1000) i;
+
+INSERT INTO distr2
+SELECT i, i*10, 'data_' || i FROM generate_series(1, 100) i;
+
+ANALYZE distr1_p1;
+ANALYZE distr1_p2;
+ANALYZE distr2_p1;
+ANALYZE distr2_p2;
+
+SET enable_partitionwise_join TO ON;
+
+-- Test joins with async Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM distr1, distr2 WHERE distr1.i=distr2.i AND distr2.j > 90 and distr2.k like 'data%'
+ORDER BY distr2.i LIMIT 10;
+SELECT * FROM distr1, distr2 WHERE distr1.i=distr2.i AND distr2.j > 90 and distr2.k like 'data%'
+ORDER BY distr2.i LIMIT 10;
+
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM distr1 LEFT JOIN distr2 ON distr1.i=distr2.i AND distr2.k like 'data%' WHERE  distr1.i > 90
+ORDER BY distr1.i LIMIT 20;
+SELECT * FROM distr1 LEFT JOIN distr2 ON  distr1.i=distr2.i AND distr2.k like 'data%' WHERE distr1.i > 90
+ORDER BY distr1.i LIMIT 20;
+
+-- Test pruning with async Merge Append
+DELETE FROM distr2;
+INSERT INTO distr2
+SELECT i%10, i*10, 'data_' || i FROM generate_series(1, 1000) i;
+
+DEALLOCATE ALL;
+SET plan_cache_mode TO force_generic_plan;
+PREPARE async_pt_query (int, int) AS
+  SELECT * FROM distr2 WHERE i = ANY(ARRAY[$1, $2])
+  ORDER BY i,j
+  LIMIT 10;
+EXPLAIN (VERBOSE, COSTS OFF)
+	EXECUTE async_pt_query(1, 1);
+EXECUTE async_pt_query(1, 1);
+RESET plan_cache_mode;
+
+RESET enable_partitionwise_join;
+
+DROP TABLE distr1, distr2, base1, base2, base3, base4;
+
 ALTER SERVER loopback OPTIONS (DROP async_capable);
 ALTER SERVER loopback2 OPTIONS (DROP async_capable);
 
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 2937384b001..a9c66fb6d54 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5316,6 +5316,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-enable-async-merge-append" xreflabel="enable_async_merge_append">
+      <term><varname>enable_async_merge_append</varname> (<type>boolean</type>)
+      <indexterm>
+       <primary><varname>enable_async_merge_append</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Enables or disables the query planner's use of async-aware
+        merge append plan types. The default is <literal>on</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-enable-bitmapscan" xreflabel="enable_bitmapscan">
       <term><varname>enable_bitmapscan</varname> (<type>boolean</type>)
       <indexterm>
diff --git a/src/backend/executor/execAsync.c b/src/backend/executor/execAsync.c
index 6129b803370..9d4a4bfa7c1 100644
--- a/src/backend/executor/execAsync.c
+++ b/src/backend/executor/execAsync.c
@@ -17,6 +17,7 @@
 #include "executor/execAsync.h"
 #include "executor/executor.h"
 #include "executor/nodeAppend.h"
+#include "executor/nodeMergeAppend.h"
 #include "executor/nodeForeignscan.h"
 
 /*
@@ -121,6 +122,9 @@ ExecAsyncResponse(AsyncRequest *areq)
 		case T_AppendState:
 			ExecAsyncAppendResponse(areq);
 			break;
+		case T_MergeAppendState:
+			ExecAsyncMergeAppendResponse(areq);
+			break;
 		default:
 			/* If the node doesn't support async, caller messed up. */
 			elog(ERROR, "unrecognized node type: %d",
diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c
index e1b9b984a7a..7743368c20d 100644
--- a/src/backend/executor/nodeMergeAppend.c
+++ b/src/backend/executor/nodeMergeAppend.c
@@ -39,10 +39,15 @@
 #include "postgres.h"
 
 #include "executor/executor.h"
+#include "executor/execAsync.h"
 #include "executor/execPartition.h"
 #include "executor/nodeMergeAppend.h"
 #include "lib/binaryheap.h"
 #include "miscadmin.h"
+#include "storage/latch.h"
+#include "utils/wait_event.h"
+
+#define EVENT_BUFFER_SIZE                     16
 
 /*
  * We have one slot for each item in the heap array.  We use SlotNumber
@@ -54,6 +59,12 @@ typedef int32 SlotNumber;
 static TupleTableSlot *ExecMergeAppend(PlanState *pstate);
 static int	heap_compare_slots(Datum a, Datum b, void *arg);
 
+static void classify_matching_subplans(MergeAppendState *node);
+static void ExecMergeAppendAsyncBegin(MergeAppendState *node);
+static void ExecMergeAppendAsyncGetNext(MergeAppendState *node, int mplan);
+static bool ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan);
+static void ExecMergeAppendAsyncEventWait(MergeAppendState *node);
+
 
 /* ----------------------------------------------------------------
  *		ExecInitMergeAppend
@@ -70,6 +81,8 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	int			nplans;
 	int			i,
 				j;
+	Bitmapset  *asyncplans;
+	int			nasyncplans;
 
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
@@ -104,7 +117,10 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 		 * later calls to ExecFindMatchingSubPlans.
 		 */
 		if (!prunestate->do_exec_prune && nplans > 0)
+		{
 			mergestate->ms_valid_subplans = bms_add_range(NULL, 0, nplans - 1);
+			mergestate->ms_valid_subplans_identified = true;
+		}
 	}
 	else
 	{
@@ -117,6 +133,7 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 		Assert(nplans > 0);
 		mergestate->ms_valid_subplans = validsubplans =
 			bms_add_range(NULL, 0, nplans - 1);
+		mergestate->ms_valid_subplans_identified = true;
 		mergestate->ms_prune_state = NULL;
 	}
 
@@ -145,16 +162,69 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	 * the results into the mergeplanstates array.
 	 */
 	j = 0;
+	asyncplans = NULL;
+	nasyncplans = 0;
+
 	i = -1;
 	while ((i = bms_next_member(validsubplans, i)) >= 0)
 	{
 		Plan	   *initNode = (Plan *) list_nth(node->mergeplans, i);
 
+		/*
+		 * Record async subplans.  When executing EvalPlanQual, we treat them
+		 * as sync ones; don't do this when initializing an EvalPlanQual plan
+		 * tree.
+		 */
+		if (initNode->async_capable && estate->es_epq_active == NULL)
+		{
+			asyncplans = bms_add_member(asyncplans, j);
+			nasyncplans++;
+		}
+
 		mergeplanstates[j++] = ExecInitNode(initNode, estate, eflags);
 	}
 
 	mergestate->ps.ps_ProjInfo = NULL;
 
+	/* Initialize async state */
+	mergestate->ms_asyncplans = asyncplans;
+	mergestate->ms_nasyncplans = nasyncplans;
+	mergestate->ms_asyncrequests = NULL;
+	mergestate->ms_asyncresults = NULL;
+	mergestate->ms_has_asyncresults = NULL;
+	mergestate->ms_asyncremain = NULL;
+	mergestate->ms_needrequest = NULL;
+	mergestate->ms_eventset = NULL;
+	mergestate->ms_valid_asyncplans = NULL;
+
+	if (nasyncplans > 0)
+	{
+		mergestate->ms_asyncrequests = (AsyncRequest **)
+			palloc0(nplans * sizeof(AsyncRequest *));
+
+		i = -1;
+		while ((i = bms_next_member(asyncplans, i)) >= 0)
+		{
+			AsyncRequest *areq;
+
+			areq = palloc(sizeof(AsyncRequest));
+			areq->requestor = (PlanState *) mergestate;
+			areq->requestee = mergeplanstates[i];
+			areq->request_index = i;
+			areq->callback_pending = false;
+			areq->request_complete = false;
+			areq->result = NULL;
+
+			mergestate->ms_asyncrequests[i] = areq;
+		}
+
+		mergestate->ms_asyncresults = (TupleTableSlot **)
+			palloc0(nplans * sizeof(TupleTableSlot *));
+
+		if (mergestate->ms_valid_subplans_identified)
+			classify_matching_subplans(mergestate);
+	}
+
 	/*
 	 * initialize sort-key information
 	 */
@@ -216,9 +286,16 @@ ExecMergeAppend(PlanState *pstate)
 		 * run-time pruning is disabled then the valid subplans will always be
 		 * set to all subplans.
 		 */
-		if (node->ms_valid_subplans == NULL)
+		if (!node->ms_valid_subplans_identified)
+		{
 			node->ms_valid_subplans =
 				ExecFindMatchingSubPlans(node->ms_prune_state, false);
+			node->ms_valid_subplans_identified = true;
+		}
+
+		/* If there are any async subplans, begin executing them. */
+		if (node->ms_nasyncplans > 0)
+			ExecMergeAppendAsyncBegin(node);
 
 		/*
 		 * First time through: pull the first tuple from each valid subplan,
@@ -231,6 +308,16 @@ ExecMergeAppend(PlanState *pstate)
 			if (!TupIsNull(node->ms_slots[i]))
 				binaryheap_add_unordered(node->ms_heap, Int32GetDatum(i));
 		}
+
+		/* Look at async subplans */
+		i = -1;
+		while ((i = bms_next_member(node->ms_asyncplans, i)) >= 0)
+		{
+			ExecMergeAppendAsyncGetNext(node, i);
+			if (!TupIsNull(node->ms_slots[i]))
+				binaryheap_add_unordered(node->ms_heap, Int32GetDatum(i));
+		}
+
 		binaryheap_build(node->ms_heap);
 		node->ms_initialized = true;
 	}
@@ -245,7 +332,13 @@ ExecMergeAppend(PlanState *pstate)
 		 * to not pull tuples until necessary.)
 		 */
 		i = DatumGetInt32(binaryheap_first(node->ms_heap));
-		node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
+		if (bms_is_member(i, node->ms_asyncplans))
+			ExecMergeAppendAsyncGetNext(node, i);
+		else
+		{
+			Assert(bms_is_member(i, node->ms_valid_subplans));
+			node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
+		}
 		if (!TupIsNull(node->ms_slots[i]))
 			binaryheap_replace_first(node->ms_heap, Int32GetDatum(i));
 		else
@@ -261,6 +354,8 @@ ExecMergeAppend(PlanState *pstate)
 	{
 		i = DatumGetInt32(binaryheap_first(node->ms_heap));
 		result = node->ms_slots[i];
+		/*  For async plan record that we can get the next tuple */
+		node->ms_has_asyncresults = bms_del_member(node->ms_has_asyncresults, i);
 	}
 
 	return result;
@@ -340,6 +435,7 @@ void
 ExecReScanMergeAppend(MergeAppendState *node)
 {
 	int			i;
+	int			nasyncplans = node->ms_nasyncplans;
 
 	/*
 	 * If any PARAM_EXEC Params used in pruning expressions have changed, then
@@ -350,8 +446,11 @@ ExecReScanMergeAppend(MergeAppendState *node)
 		bms_overlap(node->ps.chgParam,
 					node->ms_prune_state->execparamids))
 	{
+		node->ms_valid_subplans_identified = false;
 		bms_free(node->ms_valid_subplans);
 		node->ms_valid_subplans = NULL;
+		bms_free(node->ms_valid_asyncplans);
+		node->ms_valid_asyncplans = NULL;
 	}
 
 	for (i = 0; i < node->ms_nplans; i++)
@@ -372,6 +471,361 @@ ExecReScanMergeAppend(MergeAppendState *node)
 		if (subnode->chgParam == NULL)
 			ExecReScan(subnode);
 	}
+
+	/* Reset async state */
+	if (nasyncplans > 0)
+	{
+		i = -1;
+		while ((i = bms_next_member(node->ms_asyncplans, i)) >= 0)
+		{
+			AsyncRequest *areq = node->ms_asyncrequests[i];
+
+			areq->callback_pending = false;
+			areq->request_complete = false;
+			areq->result = NULL;
+		}
+
+		bms_free(node->ms_asyncremain);
+		node->ms_asyncremain = NULL;
+		bms_free(node->ms_needrequest);
+		node->ms_needrequest = NULL;
+		bms_free(node->ms_has_asyncresults);
+		node->ms_has_asyncresults = NULL;
+	}
 	binaryheap_reset(node->ms_heap);
 	node->ms_initialized = false;
 }
+
+/* ----------------------------------------------------------------
+ *              classify_matching_subplans
+ *
+ *              Classify the node's ms_valid_subplans into sync ones and
+ *              async ones, adjust it to contain sync ones only, and save
+ *              async ones in the node's ms_valid_asyncplans.
+ * ----------------------------------------------------------------
+ */
+static void
+classify_matching_subplans(MergeAppendState *node)
+{
+	Bitmapset  *valid_asyncplans;
+
+	Assert(node->ms_valid_subplans_identified);
+	Assert(node->ms_valid_asyncplans == NULL);
+
+	/* Nothing to do if there are no valid subplans. */
+	if (bms_is_empty(node->ms_valid_subplans))
+	{
+		node->ms_asyncremain = NULL;
+		return;
+	}
+
+	/* Nothing to do if there are no valid async subplans. */
+	if (!bms_overlap(node->ms_valid_subplans, node->ms_asyncplans))
+	{
+		node->ms_asyncremain = NULL;
+		return;
+	}
+
+	/* Get valid async subplans. */
+	valid_asyncplans = bms_intersect(node->ms_asyncplans,
+								   node->ms_valid_subplans);
+
+	/* Adjust the valid subplans to contain sync subplans only. */
+	node->ms_valid_subplans = bms_del_members(node->ms_valid_subplans,
+											  valid_asyncplans);
+
+	/* Save valid async subplans. */
+	node->ms_valid_asyncplans = valid_asyncplans;
+}
+
+/* ----------------------------------------------------------------
+ *              ExecMergeAppendAsyncBegin
+ *
+ *              Begin executing designed async-capable subplans.
+ * ----------------------------------------------------------------
+ */
+static void
+ExecMergeAppendAsyncBegin(MergeAppendState *node)
+{
+	int			i;
+
+	/* Backward scan is not supported by async-aware MergeAppends. */
+	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+
+	/* We should never be called when there are no subplans */
+	Assert(node->ms_nplans > 0);
+
+	/* We should never be called when there are no async subplans. */
+	Assert(node->ms_nasyncplans > 0);
+
+	/* If we've yet to determine the valid subplans then do so now. */
+	if (!node->ms_valid_subplans_identified)
+	{
+		node->ms_valid_subplans =
+			ExecFindMatchingSubPlans(node->ms_prune_state, false);
+		node->ms_valid_subplans_identified = true;
+
+		classify_matching_subplans(node);
+	}
+
+	/* Initialize state variables. */
+	node->ms_asyncremain = bms_copy(node->ms_valid_asyncplans);
+
+	/* Nothing to do if there are no valid async subplans. */
+	if (bms_is_empty(node->ms_asyncremain))
+		return;
+
+	/* Make a request for each of the valid async subplans. */
+	i = -1;
+	while ((i = bms_next_member(node->ms_valid_asyncplans, i)) >= 0)
+	{
+		AsyncRequest *areq = node->ms_asyncrequests[i];
+
+		Assert(areq->request_index == i);
+		Assert(!areq->callback_pending);
+
+		/* Do the actual work. */
+		ExecAsyncRequest(areq);
+	}
+}
+
+/* ----------------------------------------------------------------
+ *              ExecMergeAppendAsyncGetNext
+ *
+ *              Get the next tuple from specified asynchronous subplan.
+ * ----------------------------------------------------------------
+ */
+static void
+ExecMergeAppendAsyncGetNext(MergeAppendState *node, int mplan)
+{
+	node->ms_slots[mplan] = NULL;
+
+	/* Request a tuple asynchronously. */
+	if (ExecMergeAppendAsyncRequest(node, mplan))
+		return;
+
+	/*
+	 * node->ms_asyncremain can be NULL if we have fetched tuples, but haven't
+	 * returned them yet. In this case ExecMergeAppendAsyncRequest() above just
+	 * returns tuples without performing a request.
+	 */
+	while (bms_is_member(mplan, node->ms_asyncremain))
+	{
+		CHECK_FOR_INTERRUPTS();
+
+		/* Wait or poll for async events. */
+		ExecMergeAppendAsyncEventWait(node);
+
+		/* Request a tuple asynchronously. */
+		if (ExecMergeAppendAsyncRequest(node, mplan))
+			return;
+
+		/*
+		 * Waiting until there's no async requests pending or we got some
+		 * tuples from our request
+		 */
+	}
+
+	/* No tuples */
+	return;
+}
+
+/* ----------------------------------------------------------------
+ *              ExecMergeAppendAsyncRequest
+ *
+ *              Request a tuple asynchronously.
+ * ----------------------------------------------------------------
+ */
+static bool
+ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
+{
+	Bitmapset  *needrequest;
+	int			i;
+
+	/*
+	 * If we've already fetched necessary data, just return it
+	 */
+	if (bms_is_member(mplan, node->ms_has_asyncresults))
+	{
+		node->ms_slots[mplan] = node->ms_asyncresults[mplan];
+		return true;
+	}
+
+	/*
+	 * Get a list of members which can process request and don't have data
+	 * ready.
+	 */
+	needrequest = NULL;
+	i = -1;
+	while ((i = bms_next_member(node->ms_needrequest, i)) >= 0)
+	{
+		if (!bms_is_member(i, node->ms_has_asyncresults))
+			needrequest = bms_add_member(needrequest, i);
+	}
+
+	/*
+	 * If there's no members, which still need request, no need to send it.
+	 */
+	if (bms_is_empty(needrequest))
+		return false;
+
+	/* Clear ms_needrequest flag, as we are going to send requests now */
+	node->ms_needrequest = bms_del_members(node->ms_needrequest, needrequest);
+
+	/* Make a new request for each of the async subplans that need it. */
+	i = -1;
+	while ((i = bms_next_member(needrequest, i)) >= 0)
+	{
+		AsyncRequest *areq = node->ms_asyncrequests[i];
+
+		/*
+		 * We've just checked that subplan doesn't already have some fetched
+		 * data
+		 */
+		Assert(!bms_is_member(i, node->ms_has_asyncresults));
+
+		/* Do the actual work. */
+		ExecAsyncRequest(areq);
+	}
+	bms_free(needrequest);
+
+	/* Return needed asynchronously-generated results if any. */
+	if (bms_is_member(mplan, node->ms_has_asyncresults))
+	{
+		node->ms_slots[mplan] = node->ms_asyncresults[mplan];
+		return true;
+	}
+
+	return false;
+}
+
+/* ----------------------------------------------------------------
+ *              ExecAsyncMergeAppendResponse
+ *
+ *              Receive a response from an asynchronous request we made.
+ * ----------------------------------------------------------------
+ */
+void
+ExecAsyncMergeAppendResponse(AsyncRequest *areq)
+{
+	MergeAppendState *node = (MergeAppendState *) areq->requestor;
+	TupleTableSlot *slot = areq->result;
+
+	/* The result should be a TupleTableSlot or NULL. */
+	Assert(slot == NULL || IsA(slot, TupleTableSlot));
+	Assert(!bms_is_member(areq->request_index, node->ms_has_asyncresults));
+
+	node->ms_asyncresults[areq->request_index] = NULL;
+	/* Nothing to do if the request is pending. */
+	if (!areq->request_complete)
+	{
+		/* The request would have been pending for a callback. */
+		Assert(areq->callback_pending);
+		return;
+	}
+
+	/* If the result is NULL or an empty slot, there's nothing more to do. */
+	if (TupIsNull(slot))
+	{
+		/* The ending subplan wouldn't have been pending for a callback. */
+		Assert(!areq->callback_pending);
+		node->ms_asyncremain = bms_del_member(node->ms_asyncremain, areq->request_index);
+		return;
+	}
+
+	node->ms_has_asyncresults = bms_add_member(node->ms_has_asyncresults, areq->request_index);
+	/* Save result so we can return it. */
+	node->ms_asyncresults[areq->request_index] = slot;
+
+	/*
+	 * Mark the subplan that returned a result as ready for a new request.  We
+	 * don't launch another one here immediately because it might complete.
+	 */
+	node->ms_needrequest = bms_add_member(node->ms_needrequest,
+										  areq->request_index);
+}
+
+/* ----------------------------------------------------------------
+ *		ExecMergeAppendAsyncEventWait
+ *
+ *		Wait or poll for file descriptor events and fire callbacks.
+ * ----------------------------------------------------------------
+ */
+static void
+ExecMergeAppendAsyncEventWait(MergeAppendState *node)
+{
+	int			nevents = node->ms_nasyncplans + 1; /* one for PM death */
+	WaitEvent	occurred_event[EVENT_BUFFER_SIZE];
+	int			noccurred;
+	int			i;
+
+	/* We should never be called when there are no valid async subplans. */
+	Assert(bms_num_members(node->ms_asyncremain) > 0);
+
+	node->ms_eventset = CreateWaitEventSet(CurrentResourceOwner, nevents);
+	AddWaitEventToSet(node->ms_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
+					  NULL, NULL);
+
+	/* Give each waiting subplan a chance to add an event. */
+	i = -1;
+	while ((i = bms_next_member(node->ms_asyncplans, i)) >= 0)
+	{
+		AsyncRequest *areq = node->ms_asyncrequests[i];
+
+		if (areq->callback_pending)
+			ExecAsyncConfigureWait(areq);
+	}
+
+	/*
+	 * No need for further processing if there are no configured events other
+	 * than the postmaster death event.
+	 */
+	if (GetNumRegisteredWaitEvents(node->ms_eventset) == 1)
+	{
+		FreeWaitEventSet(node->ms_eventset);
+		node->ms_eventset = NULL;
+		return;
+	}
+
+	/* We wait on at most EVENT_BUFFER_SIZE events. */
+	if (nevents > EVENT_BUFFER_SIZE)
+		nevents = EVENT_BUFFER_SIZE;
+
+	/*
+	 * Wait until at least one event occurs.
+	 */
+	noccurred = WaitEventSetWait(node->ms_eventset, -1 /* no timeout */, occurred_event,
+								 nevents, WAIT_EVENT_APPEND_READY);
+	FreeWaitEventSet(node->ms_eventset);
+	node->ms_eventset = NULL;
+	if (noccurred == 0)
+		return;
+
+	/* Deliver notifications. */
+	for (i = 0; i < noccurred; i++)
+	{
+		WaitEvent  *w = &occurred_event[i];
+
+		/*
+		 * Each waiting subplan should have registered its wait event with
+		 * user_data pointing back to its AsyncRequest.
+		 */
+		if ((w->events & WL_SOCKET_READABLE) != 0)
+		{
+			AsyncRequest *areq = (AsyncRequest *) w->user_data;
+
+			if (areq->callback_pending)
+			{
+				/*
+				 * Mark it as no longer needing a callback.  We must do this
+				 * before dispatching the callback in case the callback resets
+				 * the flag.
+				 */
+				areq->callback_pending = false;
+
+				/* Do the actual work. */
+				ExecAsyncNotify(areq);
+			}
+		}
+	}
+}
diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c
index 79991b19807..f9557a8281f 100644
--- a/src/backend/optimizer/path/costsize.c
+++ b/src/backend/optimizer/path/costsize.c
@@ -152,6 +152,7 @@ bool		enable_parallel_hash = true;
 bool		enable_partition_pruning = true;
 bool		enable_presorted_aggregate = true;
 bool		enable_async_append = true;
+bool		enable_async_merge_append = true;
 
 typedef struct
 {
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index d1d259e802a..977f1ea4896 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1448,6 +1448,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	ListCell   *subpaths;
 	RelOptInfo *rel = best_path->path.parent;
 	PartitionPruneInfo *partpruneinfo = NULL;
+	bool		consider_async = false;
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1462,6 +1463,9 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->righttree = NULL;
 	node->apprelids = rel->relids;
 
+	consider_async = (enable_async_merge_append &&
+					  !best_path->path.parallel_safe &&
+					  list_length(best_path->subpaths) > 1);
 	/*
 	 * Compute sort column info, and adjust MergeAppend's tlist as needed.
 	 * Because we pass adjust_tlist_in_place = true, we may ignore the
@@ -1537,6 +1541,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 			subplan = (Plan *) sort;
 		}
 
+		/* If needed, check to see if subplan can be executed asynchronously */
+		if (consider_async)
+			mark_async_capable_plan(subplan, subpath);
+
 		subplans = lappend(subplans, subplan);
 	}
 
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 79ecaa4c4c2..836aaf60028 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -986,6 +986,16 @@ struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_async_merge_append", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of async merge append plans."),
+			NULL,
+			GUC_EXPLAIN
+		},
+		&enable_async_merge_append,
+		true,
+		NULL, NULL, NULL
+	},
 	{
 		{"enable_group_by_reordering", PGC_USERSET, QUERY_TUNING_METHOD,
 			gettext_noop("Enables reordering of GROUP BY keys."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 667e0dc40a2..124b6a9f895 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -392,6 +392,7 @@
 # - Planner Method Configuration -
 
 #enable_async_append = on
+#enable_async_merge_append = on
 #enable_bitmapscan = on
 #enable_gathermerge = on
 #enable_hashagg = on
diff --git a/src/include/executor/nodeMergeAppend.h b/src/include/executor/nodeMergeAppend.h
index c39a9fc0cb2..4371426bea1 100644
--- a/src/include/executor/nodeMergeAppend.h
+++ b/src/include/executor/nodeMergeAppend.h
@@ -19,5 +19,6 @@
 extern MergeAppendState *ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags);
 extern void ExecEndMergeAppend(MergeAppendState *node);
 extern void ExecReScanMergeAppend(MergeAppendState *node);
+extern void ExecAsyncMergeAppendResponse(AsyncRequest *areq);
 
 #endif							/* NODEMERGEAPPEND_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 87f1519ec65..e48ab044581 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1488,10 +1488,66 @@ typedef struct MergeAppendState
 	TupleTableSlot **ms_slots;	/* array of length ms_nplans */
 	struct binaryheap *ms_heap; /* binary heap of slot indices */
 	bool		ms_initialized; /* are subplans started? */
+	Bitmapset  *ms_asyncplans;	/* asynchronous plans indexes */
+	int			ms_nasyncplans; /* # of asynchronous plans */
+	AsyncRequest **ms_asyncrequests;	/* array of AsyncRequests */
+	TupleTableSlot **ms_asyncresults;	/* unreturned results of async plans */
+	Bitmapset   *ms_has_asyncresults;	/* plans which have async results */
+	Bitmapset  *ms_asyncremain; /* remaining asynchronous plans */
+	Bitmapset  *ms_needrequest; /* asynchronous plans needing a new request */
+	struct WaitEventSet *ms_eventset;	/* WaitEventSet used to configure file
+										 * descriptor wait events */
 	struct PartitionPruneState *ms_prune_state;
+	bool		ms_valid_subplans_identified;   /* is ms_valid_subplans valid? */
 	Bitmapset  *ms_valid_subplans;
+	Bitmapset  *ms_valid_asyncplans;	/* valid asynchronous plans indexes */
 } MergeAppendState;
 
+/* Getters for AppendState and MergeAppendState */
+static inline struct WaitEventSet *
+GetAppendEventSet(PlanState *ps)
+{
+	Assert (IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *)ps)->as_eventset;
+	else
+		return ((MergeAppendState *)ps)->ms_eventset;
+}
+
+static inline Bitmapset *
+GetNeedRequest(PlanState *ps)
+{
+	Assert (IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *)ps)->as_needrequest;
+	else
+		return ((MergeAppendState *)ps)->ms_needrequest;
+}
+
+static inline Bitmapset *
+GetValidAsyncplans(PlanState *ps)
+{
+	Assert (IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *)ps)->as_valid_asyncplans;
+	else
+		return ((MergeAppendState *)ps)->ms_valid_asyncplans;
+}
+
+static inline AsyncRequest*
+GetValidAsyncRequest(PlanState *ps, int nreq)
+{
+	Assert (IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *)ps)->as_asyncrequests[nreq];
+	else
+		return ((MergeAppendState *)ps)->ms_asyncrequests[nreq];
+}
+
 /* ----------------
  *	 RecursiveUnionState information
  *
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index 57861bfb446..e95a8e36dca 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -70,6 +70,7 @@ extern PGDLLIMPORT bool enable_parallel_hash;
 extern PGDLLIMPORT bool enable_partition_pruning;
 extern PGDLLIMPORT bool enable_presorted_aggregate;
 extern PGDLLIMPORT bool enable_async_append;
+extern PGDLLIMPORT bool enable_async_merge_append;
 extern PGDLLIMPORT int constraint_exclusion;
 
 extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index fad7fc3a7e0..d5105bc28a8 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -149,6 +149,7 @@ select name, setting from pg_settings where name like 'enable%';
               name              | setting 
 --------------------------------+---------
  enable_async_append            | on
+ enable_async_merge_append      | on
  enable_bitmapscan              | on
  enable_gathermerge             | on
  enable_group_by_reordering     | on
@@ -170,7 +171,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(22 rows)
+(23 rows)
 
 -- There are always wait event descriptions for various types.  InjectionPoint
 -- may be present or absent, depending on history since last postmaster start.
-- 
2.34.1

From 23b95137343206c2e18578357b5bf1850744b48d Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Fri, 21 Jul 2023 12:05:07 +0300
Subject: [PATCH 1/2] mark_async_capable(): subpath should match subplan

---
 src/backend/optimizer/plan/createplan.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 28addc1129a..d1d259e802a 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1147,10 +1147,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
-				 * If the generated plan node includes a gating Result node,
-				 * we can't execute it asynchronously.
+				 * If the generated plan node includes a gating Result node or
+				 * a Sort node, we can't execute it asynchronously.
 				 */
-				if (IsA(plan, Result))
+				if (IsA(plan, Result) || IsA(plan, Sort))
 					return false;
 
 				/*
@@ -1168,10 +1168,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
-				 * If the generated plan node includes a gating Result node,
-				 * we can't execute it asynchronously.
+				 * If the generated plan node includes a gating Result node or
+				 * a Sort node, we can't execute it asynchronously.
 				 */
-				if (IsA(plan, Result))
+				if (IsA(plan, Result) || IsA(plan, Sort))
 					return false;
 
 				Assert(fdwroutine != NULL);
@@ -1184,9 +1184,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 			 * If the generated plan node includes a Result node for the
-			 * projection, we can't execute it asynchronously.
+			 * projection or a Sort node, we can't execute it asynchronously.
 			 */
-			if (IsA(plan, Result))
+			if (IsA(plan, Result) || IsA(plan, Sort))
 				return false;
 
 			/*
-- 
2.34.1

---

From: Alexander Pyhalov <[email-masked]>
Date: Sat, 26 Jul 2025 10:56:22 +0300

Hi.

I've updated patches for asynchronous merge append. They allowed us to 
significantly improve performance in practice. Earlier select from 
partitioned (and distributed table) could switch to synchronous merge 
append plan from asynchronous append. Given that table could have 20+ 
partitions, it was cheaper, but much less efficient due to remote parts 
executing synchronously.

In this version there's a couple of small fixes - earlier 
ExecMergeAppend() scanned all asyncplans, but should do this only for 
valid asyncplans. Also incorporated logic from

commit af717317a04f5217728ce296edf4a581eb7e6ea0
Author: Heikki Linnakangas <[email-masked]>
Date:   Wed Mar 12 20:53:09 2025 +0200

     Handle interrupts while waiting on Append's async subplans

into ExecMergeAppendAsyncEventWait().

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From fe64d52c836eb1120d7446d9f1ea1ea5b27b0bbf Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 26 Jul 2025 10:43:57 +0300
Subject: [PATCH 2/2] MergeAppend should support Async Foreign Scan subplans

---
 .../postgres_fdw/expected/postgres_fdw.out    | 247 +++++++++
 contrib/postgres_fdw/postgres_fdw.c           |  10 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     |  78 +++
 doc/src/sgml/config.sgml                      |  14 +
 src/backend/executor/execAsync.c              |   4 +
 src/backend/executor/nodeMergeAppend.c        | 481 +++++++++++++++++-
 src/backend/optimizer/path/costsize.c         |   1 +
 src/backend/optimizer/plan/createplan.c       |   9 +
 src/backend/utils/misc/guc_tables.c           |  10 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/executor/nodeMergeAppend.h        |   1 +
 src/include/nodes/execnodes.h                 |  56 ++
 src/include/optimizer/cost.h                  |   1 +
 src/test/regress/expected/sysviews.out        |   3 +-
 14 files changed, 910 insertions(+), 6 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 4b6e49a5d95..ca5f0926e22 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11453,6 +11453,46 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -11496,6 +11536,35 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -11531,6 +11600,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -12313,6 +12413,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
index 25b287be069..8438d67a6be 100644
@@ -7213,12 +7213,16 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)

@@ -7256,7 +7260,7 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)
index 31b6c685b55..55708af4736 100644
@@ -3861,6 +3861,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
@@ -3881,6 +3886,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
 
@@ -3896,6 +3906,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4134,6 +4149,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 20ccb2d6b54..3a83f2eddd9 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5443,6 +5443,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
index 5d3cabe73e3..6dc19ebc374 100644
 
 /*
index 405e8f94285..6f899a2d5f5 100644

 /*

 /* ----------------------------------------------------------------
  *		ExecInitMergeAppend
@@ -71,6 +82,8 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	int			nplans;
 	int			i,
 				j;
+	Bitmapset  *asyncplans;
+	int			nasyncplans;
 
@@ -106,7 +119,10 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
@@ -119,6 +135,7 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 
@@ -135,11 +152,25 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	 * the results into the mergeplanstates array.
 	 */
 	j = 0;
+	asyncplans = NULL;
+	nasyncplans = 0;
+
 	i = -1;
 	while ((i = bms_next_member(validsubplans, i)) >= 0)
 	{
 		Plan	   *initNode = (Plan *) list_nth(node->mergeplans, i);
 
+		/*
 
@@ -170,6 +201,45 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	 */
 	mergestate->ps.ps_ProjInfo = NULL;
 
@@ -231,9 +301,16 @@ ExecMergeAppend(PlanState *pstate)
 				ExecFindMatchingSubPlans(node->ms_prune_state, false, NULL);
 
 		/*
@@ -246,6 +323,16 @@ ExecMergeAppend(PlanState *pstate)
+		/* Look at valid async subplans */
@@ -260,7 +347,13 @@ ExecMergeAppend(PlanState *pstate)
@@ -276,6 +369,8 @@ ExecMergeAppend(PlanState *pstate)
 
 	return result;
@@ -355,6 +450,7 @@ void
 
 	/*
@@ -365,8 +461,11 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -387,6 +486,384 @@ ExecReScanMergeAppend(MergeAppendState *node)
+			ExecFindMatchingSubPlans(node->ms_prune_state, false, NULL);
+	 * returned them yet. In this case ExecMergeAppendAsyncRequest() above
+	 * just returns tuples without performing a request.
+	int			nevents = node->ms_nasyncplans + 2; /* one for PM death and
+													 * one for latch */
+	 * No need for further processing if none of the subplans configured any
+	 * events.
+	 * Add the process latch to the set, so that we wake up to process the
+	 * standard interrupts with CHECK_FOR_INTERRUPTS().
+	 * NOTE: For historical reasons, it's important that this is added to the
+	 * WaitEventSet after the ExecAsyncConfigureWait() calls.  Namely,
+	 * postgres_fdw calls "GetNumRegisteredWaitEvents(set) == 1" to check if
+	 * any other events are in the set.  That's a poor design, it's
+	 * questionable for postgres_fdw to be doing that in the first place, but
+	 * we cannot change it now.  The pattern has possibly been copied to other
+	 * extensions too.
+	AddWaitEventToSet(node->ms_eventset, WL_LATCH_SET, PGINVALID_SOCKET,
+					  MyLatch, NULL);
+	/* Return at most EVENT_BUFFER_SIZE events in one call. */
+	noccurred = WaitEventSetWait(node->ms_eventset, -1 /* no timeout */ , occurred_event,
+		/* Handle standard interrupts */
+		if ((w->events & WL_LATCH_SET) != 0)
+			ResetLatch(MyLatch);
index 1f04a2c182c..4c2c2a92ec9 100644
@@ -163,6 +163,7 @@ bool		enable_parallel_hash = true;
 
 typedef struct
 {
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index deaf763fd44..bea58bd46f8 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1471,6 +1471,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
 	RelOptInfo *rel = best_path->path.parent;
+	bool		consider_async = false;
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1485,6 +1486,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->righttree = NULL;
 	node->apprelids = rel->relids;
 
@@ -1585,6 +1590,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 			subplan = sort_plan;
 		}

diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index d14b1678e7f..00d967c0f24 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -1006,6 +1006,16 @@ struct config_bool ConfigureNamesBool[] =
 		true,
 		NULL, NULL, NULL
 	},
+	{
+		{"enable_async_merge_append", PGC_USERSET, QUERY_TUNING_METHOD,
+			gettext_noop("Enables the planner's use of async merge append plans."),
+			NULL,
+			GUC_EXPLAIN
+		},
+		&enable_async_merge_append,
+		true,
+		NULL, NULL, NULL
+	},
 	{
 		{"enable_self_join_elimination", PGC_USERSET, QUERY_TUNING_METHOD,
 			gettext_noop("Enables removal of unique self-joins."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index a9d8293474a..bfa332a098c 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -405,6 +405,7 @@
 # - Planner Method Configuration -
 
index 4eb05dc30d6..e3fdb26ece6 100644
 
index e107d6e5f81..097559006af 100644
@@ -1544,10 +1544,66 @@ typedef struct MergeAppendState
 
index b523bcda8f3..fee491b77ad 100644
 
 extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 83228cfca29..2a55efd6605 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -149,6 +149,7 @@ select name, setting from pg_settings where name like 'enable%';
               name              | setting 
 --------------------------------+---------
  enable_async_append            | on
+ enable_async_merge_append      | on
  enable_bitmapscan              | on
  enable_distinct_reordering     | on
  enable_gathermerge             | on
@@ -172,7 +173,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(24 rows)
+(25 rows)
 
2.43.0

From 350cf61067261601444c813ed89b47adf0cc65e5 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Fri, 21 Jul 2023 12:05:07 +0300
Subject: [PATCH 1/2] mark_async_capable(): subpath should match subplan

---

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 8a9f1d7a943..deaf763fd44 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1146,10 +1146,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
 
 				/*
@@ -1167,10 +1167,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
 
 				Assert(fdwroutine != NULL);
@@ -1183,9 +1183,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 
 			/*
-- 
2.43.0

---

From: "Matheus Alcantara" <[email-masked]>
Date: Mon, 03 Nov 2025 10:00:48 -0300

Hi, thanks for working on this!

On Tue Aug 20, 2024 at 6:14 AM -03, Alexander Pyhalov wrote:
> [...]
I ran some benchmarks based on v4 attached by Alvaro in [1] using a
smaller number of threads so that some CPU cores would be idle and I
also obtained better results:

tps = 4301.567405 

Master, async_capable on:
tps = 3847.084545

So I'm +1 for the idea. I know it's been while since the last patch, and
unfortunully it hasn't received reviews since then. Do you still plan to
work on it? I still need to take a look on the code to see if I can help
with some comments.

During the tests I got compiler errors due to fce7c73fba4, so I'm
attaching a v5 with guc_parameters.dat correctly sorted. 

The postgres_fdw/regress tests was also failling due to some whitespace
problems, v5 also fix this.

[1] https://www.postgresql.org/message-id/202510251154.isknefznk566%40alvherre.pgsql

--
Matheus Alcantara

From 27e9f6f89ee421f29ca8ee669845a910c8e3f74a Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Fri, 21 Jul 2023 12:05:07 +0300
Subject: [PATCH v5 1/2] mark_async_capable(): subpath should match subplan

---

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 8af091ba647..004bbc6d1d6 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1139,10 +1139,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
 
 				/*
@@ -1160,10 +1160,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
 
 				Assert(fdwroutine != NULL);
@@ -1176,9 +1176,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 
 			/*
-- 
2.51.0

From dd2aace9540d46165a81695e6df817fc4d80dd5b Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 26 Jul 2025 10:43:57 +0300
Subject: [PATCH v5 2/2] MergeAppend should support Async Foreign Scan subplans

---
 src/backend/utils/misc/guc_parameters.dat     |   8 +
 14 files changed, 908 insertions(+), 6 deletions(-)

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index cd28126049d..d5f25a6de9a 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11556,6 +11556,46 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -11604,6 +11644,35 @@ COPY async_pt TO stdout; --error
 ERROR:  cannot copy from foreign table "async_p1"
 DETAIL:  Partition "async_p1" is a foreign table in partitioned table "async_pt"
 HINT:  Try the COPY (SELECT ...) TO variant.
@@ -11639,6 +11708,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -12421,6 +12521,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
index 456b267f70b..a63eb002416 100644

index 9a8f9e28135..0786ba2c502 100644
@@ -3921,6 +3921,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+
 -- Test error handling, if accessing one of the foreign partitions errors out
 CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
   SERVER loopback OPTIONS (table_name 'non_existent_table');
@@ -3944,6 +3949,11 @@ DELETE FROM result_tbl;
 -- Test COPY TO when foreign table is partition
 COPY async_pt TO stdout; --error
 
+-- Test Merge Append
 
@@ -3959,6 +3969,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4197,6 +4212,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 06d1e4403b5..3e7745f0b32 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5444,6 +5444,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>

 /*

 /*

 

+		/*

 
 		/*
 
 	return result;
@@ -355,6 +450,7 @@ void
 
 	/*
 
index 8335cf5b5c5..cfbe512a26e 100644
 
 typedef struct
 {
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 004bbc6d1d6..98880e6008f 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1464,6 +1464,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
 	RelOptInfo *rel = best_path->path.parent;
+	bool		consider_async = false;
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1478,6 +1479,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->righttree = NULL;
 	node->apprelids = rel->relids;
 
@@ -1578,6 +1583,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 			subplan = sort_plan;
 		}

diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 25da769eb35..dd060f897c5 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -805,6 +805,14 @@
   boot_val => 'true',
 },
 
+{ name => 'enable_async_merge_append', type => 'bool', context => 'PGC_USERSET', group => 'QUERY_TUNING_METHOD',
+  short_desc => 'Enables the planner\'s use of async merge append plans.',
+  flags => 'GUC_EXPLAIN',
+  variable => 'enable_async_merge_append',
+  boot_val => 'true',
+},
+
+
 { name => 'enable_bitmapscan', type => 'bool', context => 'PGC_USERSET', group => 'QUERY_TUNING_METHOD',
   short_desc => 'Enables the planner\'s use of bitmap-scan plans.',
   flags => 'GUC_EXPLAIN',
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index f62b61967ef..daa26d6890b 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -405,6 +405,7 @@
 # - Planner Method Configuration -

index 18ae8f0d4bb..121cede229e 100644
@@ -1545,10 +1545,66 @@ typedef struct MergeAppendState
 
+/* Getters for AppendState and MergeAppendState */
+static inline struct WaitEventSet *
+GetAppendEventSet(PlanState *ps)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_eventset;
+	else
+		return ((MergeAppendState *) ps)->ms_eventset;
+}
+
+static inline Bitmapset *
+GetNeedRequest(PlanState *ps)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_needrequest;
+	else
+		return ((MergeAppendState *) ps)->ms_needrequest;
+}
+
+static inline Bitmapset *
+GetValidAsyncplans(PlanState *ps)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_valid_asyncplans;
+	else
+		return ((MergeAppendState *) ps)->ms_valid_asyncplans;
+}
+
+static inline AsyncRequest *
+GetValidAsyncRequest(PlanState *ps, int nreq)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_asyncrequests[nreq];
+	else
+		return ((MergeAppendState *) ps)->ms_asyncrequests[nreq];
+}
+
 /* ----------------
  *	 RecursiveUnionState information
  *
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index b523bcda8f3..fee491b77ad 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -70,6 +70,7 @@ extern PGDLLIMPORT bool enable_parallel_hash;
 extern PGDLLIMPORT bool enable_partition_pruning;
 extern PGDLLIMPORT bool enable_presorted_aggregate;
 extern PGDLLIMPORT bool enable_async_append;
+extern PGDLLIMPORT bool enable_async_merge_append;
 extern PGDLLIMPORT int constraint_exclusion;
 
 extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 3b37fafa65b..ae4fa42a438 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -149,6 +149,7 @@ select name, setting from pg_settings where name like 'enable%';
               name              | setting 
 --------------------------------+---------
  enable_async_append            | on
+ enable_async_merge_append      | on
  enable_bitmapscan              | on
  enable_distinct_reordering     | on
  enable_eager_aggregate         | on
@@ -173,7 +174,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(25 rows)
+(26 rows)
 
2.51.0

---

From: Alexander Pyhalov <[email-masked]>
Date: Wed, 05 Nov 2025 09:30:59 +0300

Hi.

Matheus Alcantara писал(а) 2025-11-03 16:00:
> [1] 
> https://www.postgresql.org/message-id/202510251154.isknefznk566%40alvherre.pgsql
> 

I'm still interested in working on this patch, but it didn't get any 
review (besides internal one). I suppose, Append and MergeAppend nodes 
need some unification, for example, ExecAppendAsyncEventWait and 
ExecMergeAppendAsyncEventWait looks the same, both 
classify_matching_subplans() versions are suspiciously similar. But 
honestly, patch needs thorough review.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: "Matheus Alcantara" <[email-masked]>
Date: Tue, 11 Nov 2025 18:00:53 -0300

On Wed Nov 5, 2025 at 3:30 AM -03, Alexander Pyhalov wrote:
>> So I'm +1 for the idea. I know it's been while since the last patch,
>> and unfortunully it hasn't received reviews since then. Do you still
>> plan to work on it? I still need to take a look on the code to see if
>> I can help with some comments.
>
Here are some comments on my first look at the patches. I still don't
have too much experience with the executor code but I hope that I can
help with something.

v5-0001-mark_async_capable-subpath-should-match-subplan.patch

I don't have to much comments on this, perhaps we could have a commit
message explaining the reason behind the change. 

----

v5-0002-MergeAppend-should-support-Async-Foreign-Scan-sub.patch

The AppendState struct has the "as_syncdone", this field is not needed
on MergeAppendState?

----
Regarding the duplicated code on classify_matching_subplans I think that
we can have a more generic function that operates over function
parameters, something like this:

/*
 * Classify valid subplans into sync and async groups.
 *
 * It calculates the intersection of *valid_subplans and *asyncplans,
 * stores the result in *valid_asyncplans, and removes those members
 * from *valid_subplans (leaving only sync plans).
 *
 * Returns true if valid async plans were found, false otherwise.
 */
static bool
classify_subplans_internal(Bitmapset **valid_subplans,
                       Bitmapset *asyncplans,
                       Bitmapset **valid_asyncplans);

----
The GetValidAsyncplans() is not being used

----
We have some reduction of code coverage on nodeMergeAppend.c. The
significant blocks are on ExecMergeAppendAsyncBegin():
+	/* If we've yet to determine the valid subplans then do so now. */
+	if (!node->ms_valid_subplans_identified)
+	{
+		node->ms_valid_subplans =
+			ExecFindMatchingSubPlans(node->ms_prune_state, false, NULL);
+		node->ms_valid_subplans_identified = true;
+
+		classify_matching_subplans(node);
+	}

And there are some blocks on ExecReScanMergeAppend(). It's worth adding
a test case for then? I'm not sure how hard would be to write a
regression test that cover these blocks.

----
I agree that duplicated code is not good but it seems to me that we
already have some code on nodeMergeAppend.c borrowed from nodeAppend.c
even without you patch, for example the ExecInitMergeAppend(),
ExecReScanMergeAppend() and partially ExecMergeAppend().

Although nodeMergeAppend.c and nodeAppend.c have similar functions ,
some difference exists and I'm wondering if we should wait for the rule
of three [1] to refactor these duplicated code?

[1] https://en.wikipedia.org/wiki/Rule_of_three_(computer_programming)

--
Matheus Alcantara
EDB: http://www.enterprisedb.com

---

From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 13:57:04 +0300

>> honestly, patch needs thorough review.

Hi.
Thanks for review.

> message explaining the reason behind the change.

I've expanded commit message. The issue is that mark_async_capable() 
relies
on the fact that plan node type corresponds to path type. This is not 
true when
(Merge)Append decides to insert Sort node.

> The AppendState struct has the "as_syncdone", this field is not needed

We don't need as_syncdone. Async Append fetches tuple from async subplan 
and waits for them either when they have some data or when there's no 
more sync subplans (as we can return any tuple we receive from 
subplans). But ExecMergeAppend should decide which tuple to return based 
on sort order, so there's no need to remember if we are done with sync 
subplans, as subplans ordering matters, and we can't arbitrary switch 
between them.

> parameters

I've tried to do so, but there are two issues. There's no suitable 
common header between
nodAppend and nodeMergeAppend. I've put 
classify_matching_subplans_common() into src/include/nodes/execnodes.h
and sure that it's not the best choice. The second issue is with 
as_syncdone, it exists only in AppendState, so
we should check for empty valid_subplans separately. In fact, there's 3 
outcomes for Append 1) no sync plans,
no async plans,  2) no async plans, 3) async plans present, and only 
last two states have meaning
for MergeAppend.

> The GetValidAsyncplans() is not being used

As well as GetValidAsyncRequest(), these parts are used by our FDW, so 
they slipped in the patch. Removed them.

> regression test that cover these blocks.

You are right. There's difference between ExecAppend and 
ExecMergeAppend. Append identifies valid subplans in 
ExecAppendAsyncBegin. MergeAppend - earlier, in ExecMergeAppend(). So 
this is really the dead code. And there was an issue with it, which 
became evident when I've added test for rescan. When we've identified 
new subplans in ExecMergeAppend(), we have to classify them.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From 044ff10f402c0cbc4f815a34fc266e4e581274c0 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH 1/2] mark_async_capable(): subpath should match subplan

create_append_plan() calls mark_async_capable() on subplan of
Append and corresponding subpath. Later mark_async_capable()
looks at path type and decides that subplan has type, corresponding
to the path type. However, this is not true if create_append_plan()
inserts Sort node above Append subplan. So we should handle such case
separately.
---
 src/backend/optimizer/plan/createplan.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

 				/*
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.43.0

From 0769f07f42d85275b4a5a2e14d44fc4a7891ef9b Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH 2/2] MergeAppend should support Async Foreign Scan subplans

---
 .../postgres_fdw/expected/postgres_fdw.out    | 288 +++++++++++
 contrib/postgres_fdw/postgres_fdw.c           |  10 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     |  87 ++++
 doc/src/sgml/config.sgml                      |  14 +
 src/backend/executor/execAsync.c              |   4 +
 src/backend/executor/nodeAppend.c             |  21 +-
 src/backend/executor/nodeMergeAppend.c        | 458 +++++++++++++++++-
 src/backend/optimizer/path/costsize.c         |   1 +
 src/backend/optimizer/plan/createplan.c       |   9 +
 src/backend/utils/misc/guc_parameters.dat     |   8 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/executor/nodeMergeAppend.h        |   1 +
 src/include/nodes/execnodes.h                 |  57 +++
 src/include/optimizer/cost.h                  |   1 +
 src/test/regress/expected/sysviews.out        |   3 +-
 15 files changed, 938 insertions(+), 25 deletions(-)

index cd28126049d..5aa563c95ed 100644
 
 DELETE FROM result_tbl;
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+                                                          QUERY PLAN                                                          
+------------------------------------------------------------------------------------------------------------------------------
+ Merge Append
+   Sort Key: async_pt.b, async_pt.a
+   ->  Async Foreign Scan on public.async_p1 async_pt_1
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         Remote SQL: SELECT a, b, c FROM public.base_tbl1 WHERE (((b % 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p2 async_pt_2
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         Remote SQL: SELECT a, b, c FROM public.base_tbl2 WHERE (((b % 100) = 0)) ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+(8 rows)
+
+SELECT * FROM async_pt WHERE b % 100 = 0 ORDER BY b, a;
+  a   |  b  |  c   
+------+-----+------
+ 1000 |   0 | 0000
+ 2000 |   0 | 0000
+ 1100 | 100 | 0100
+ 2100 | 100 | 0100
+ 1200 | 200 | 0200
+ 2200 | 200 | 0200
+ 1300 | 300 | 0300
+ 2300 | 300 | 0300
+ 1400 | 400 | 0400
+ 2400 | 400 | 0400
+ 1500 | 500 | 0500
+ 2500 | 500 | 0500
+ 1600 | 600 | 0600
+ 2600 | 600 | 0600
+ 1700 | 700 | 0700
+ 2700 | 700 | 0700
+ 1800 | 800 | 0800
+ 2800 | 800 | 0800
+ 1900 | 900 | 0900
+ 2900 | 900 | 0900
+(20 rows)
+
 -- Test error handling, if accessing one of the foreign partitions errors out
 CREATE FOREIGN TABLE async_p_broken PARTITION OF async_pt FOR VALUES FROM (10000) TO (10001)
   SERVER loopback OPTIONS (table_name 'non_existent_table');
@@ -11604,6 +11644,76 @@ COPY async_pt TO stdout; --error
 ERROR:  cannot copy from foreign table "async_p1"
 DETAIL:  Partition "async_p1" is a foreign table in partitioned table "async_pt"
 HINT:  Try the COPY (SELECT ...) TO variant.
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+                                              QUERY PLAN                                              
+------------------------------------------------------------------------------------------------------
+ Merge Append
+   Sort Key: async_pt.b, async_pt.a
+   ->  Async Foreign Scan on public.async_p1 async_pt_1
+         Output: async_pt_1.a, async_pt_1.b, async_pt_1.c
+         Filter: (async_pt_1.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl1 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p2 async_pt_2
+         Output: async_pt_2.a, async_pt_2.b, async_pt_2.c
+         Filter: (async_pt_2.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl2 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+   ->  Async Foreign Scan on public.async_p3 async_pt_3
+         Output: async_pt_3.a, async_pt_3.b, async_pt_3.c
+         Filter: (async_pt_3.b === 505)
+         Remote SQL: SELECT a, b, c FROM public.base_tbl3 ORDER BY b ASC NULLS LAST, a ASC NULLS LAST
+(14 rows)
+
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+  a   |  b  |  c   
+------+-----+------
+ 1505 | 505 | 0505
+ 2505 | 505 | 0505
+ 3505 | 505 | 0505
+(3 rows)
+
+-- Test async Merge Append rescan
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT
+	ARRAY(SELECT f.i FROM (SELECT b + g.i FROM async_pt WHERE a > g.i ORDER BY b) f(i) ORDER BY f.i LIMIT 10)
+FROM generate_series(1, 3) g(i);
+                                                            QUERY PLAN                                                            
+----------------------------------------------------------------------------------------------------------------------------------
+ Function Scan on pg_catalog.generate_series g
+   Output: ARRAY(SubPlan array_1)
+   Function Call: generate_series(1, 3)
+   SubPlan array_1
+     ->  Limit
+           Output: f.i
+           ->  Sort
+                 Output: f.i
+                 Sort Key: f.i
+                 ->  Subquery Scan on f
+                       Output: f.i
+                       ->  Merge Append
+                             Sort Key: async_pt.b
+                             ->  Async Foreign Scan on public.async_p1 async_pt_1
+                                   Output: (async_pt_1.b + g.i), async_pt_1.b
+                                   Remote SQL: SELECT b FROM public.base_tbl1 WHERE ((a > $1::integer)) ORDER BY b ASC NULLS LAST
+                             ->  Async Foreign Scan on public.async_p2 async_pt_2
+                                   Output: (async_pt_2.b + g.i), async_pt_2.b
+                                   Remote SQL: SELECT b FROM public.base_tbl2 WHERE ((a > $1::integer)) ORDER BY b ASC NULLS LAST
+                             ->  Async Foreign Scan on public.async_p3 async_pt_3
+                                   Output: (async_pt_3.b + g.i), async_pt_3.b
+                                   Remote SQL: SELECT b FROM public.base_tbl3 WHERE ((a > $1::integer)) ORDER BY b ASC NULLS LAST
+(22 rows)
+
+SELECT
+	ARRAY(SELECT f.i FROM (SELECT b + g.i FROM async_pt WHERE a > g.i ORDER BY b) f(i) ORDER BY f.i LIMIT 10)
+FROM generate_series(1, 3) g(i);
+           array           
+---------------------------
+ {1,1,1,6,6,6,11,11,11,16}
+ {2,2,2,7,7,7,12,12,12,17}
+ {3,3,3,8,8,8,13,13,13,18}
+(3 rows)
+
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 -- Check case where the partitioned table has local/remote partitions
@@ -11639,6 +11749,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -12421,6 +12562,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
index 06b52c65300..2105c9c90b9 100644

index 9a8f9e28135..aa388cb027f 100644
 
+-- Test Merge Append
@@ -3944,6 +3949,20 @@ DELETE FROM result_tbl;
 
+-- Test Merge Append
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+SELECT * FROM async_pt WHERE b === 505 ORDER BY b, a;
+
+-- Test async Merge Append rescan
+EXPLAIN (VERBOSE, COSTS OFF)
+SELECT
+	ARRAY(SELECT f.i FROM (SELECT b + g.i FROM async_pt WHERE a > g.i ORDER BY b) f(i) ORDER BY f.i LIMIT 10)
+FROM generate_series(1, 3) g(i);
+SELECT
+	ARRAY(SELECT f.i FROM (SELECT b + g.i FROM async_pt WHERE a > g.i ORDER BY b) f(i) ORDER BY f.i LIMIT 10)
+FROM generate_series(1, 3) g(i);
+
 DROP FOREIGN TABLE async_p3;
 DROP TABLE base_tbl3;
 
@@ -3959,6 +3978,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4197,6 +4221,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index df1c3eaaa58..1d46de13918 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5455,6 +5455,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>

 /*
@@ -121,6 +122,9 @@ ExecAsyncResponse(AsyncRequest *areq)
 		case T_AppendState:
 			ExecAsyncAppendResponse(areq);
 			break;
+		case T_MergeAppendState:
+			ExecAsyncMergeAppendResponse(areq);
+			break;
 		default:
 			/* If the node doesn't support async, caller messed up. */
 			elog(ERROR, "unrecognized node type: %d",
diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index a11b36c7176..c89e2d2787f 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1187,10 +1187,7 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 static void
 classify_matching_subplans(AppendState *node)
 {
-	Bitmapset  *valid_asyncplans;
-
 	Assert(node->as_valid_subplans_identified);
-	Assert(node->as_valid_asyncplans == NULL);
 
 	/* Nothing to do if there are no valid subplans. */
 	if (bms_is_empty(node->as_valid_subplans))
@@ -1200,21 +1197,7 @@ classify_matching_subplans(AppendState *node)
 		return;
 	}
 
-	/* Nothing to do if there are no valid async subplans. */
-	if (!bms_overlap(node->as_valid_subplans, node->as_asyncplans))
-	{
+	/* No valid async subplans identified. */
+	if (!classify_matching_subplans_common(&node->as_valid_subplans, node->as_asyncplans, &node->as_valid_asyncplans))
 		node->as_nasyncremain = 0;
-		return;
-	}
-
-	/* Get valid async subplans. */
-	valid_asyncplans = bms_intersect(node->as_asyncplans,
-									 node->as_valid_subplans);
-
-	/* Adjust the valid subplans to contain sync subplans only. */
-	node->as_valid_subplans = bms_del_members(node->as_valid_subplans,
-											  valid_asyncplans);
-
-	/* Save valid async subplans. */
-	node->as_valid_asyncplans = valid_asyncplans;
 }
diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c
index 405e8f94285..7db41fbf40f 100644
--- a/src/backend/executor/nodeMergeAppend.c
+++ b/src/backend/executor/nodeMergeAppend.c
@@ -39,10 +39,15 @@
 #include "postgres.h"

 /*

 

+		/*

@@ -231,9 +301,17 @@ ExecMergeAppend(PlanState *pstate)
 
 		/*
@@ -246,6 +324,16 @@ ExecMergeAppend(PlanState *pstate)
@@ -260,7 +348,13 @@ ExecMergeAppend(PlanState *pstate)
@@ -276,6 +370,8 @@ ExecMergeAppend(PlanState *pstate)
 
 	return result;
@@ -355,6 +451,7 @@ void
 
 	/*
@@ -365,8 +462,11 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -387,6 +487,360 @@ ExecReScanMergeAppend(MergeAppendState *node)
+	/* No valid async subplans identified. */
+	if (!classify_matching_subplans_common(&node->ms_valid_subplans, node->ms_asyncplans, &node->ms_valid_asyncplans))
+	/* ExecMergeAppend() identifies valid subplans */
 
 typedef struct
 {
 
 	/*

 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 1128167c025..2a670bd8db1 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -805,6 +805,14 @@
   boot_val => 'true',
 },
 
index 6268c175298..b2a92d8cb71 100644

index 18ae8f0d4bb..2bef54550a3 100644
@@ -1545,10 +1545,67 @@ typedef struct MergeAppendState
 
+/* Getters for AppendState and MergeAppendState */
+static inline struct WaitEventSet *
+GetAppendEventSet(PlanState *ps)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_eventset;
+	else
+		return ((MergeAppendState *) ps)->ms_eventset;
+}
+
+static inline Bitmapset *
+GetNeedRequest(PlanState *ps)
+{
+	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
+
+	if (IsA(ps, AppendState))
+		return ((AppendState *) ps)->as_needrequest;
+	else
+		return ((MergeAppendState *) ps)->ms_needrequest;
+}
+
+/* Common part of classify_matching_subplans() for Append and MergeAppend */
+static inline bool
+classify_matching_subplans_common(Bitmapset **valid_subplans, Bitmapset *asyncplans, Bitmapset **valid_asyncplans)
+{
+	Assert(*valid_asyncplans == NULL);
+
+	/* Checked by classify_matching_subplans() */
+	Assert(!bms_is_empty(*valid_subplans));
+
+	/* Nothing to do if there are no valid async subplans. */
+	if (!bms_overlap(*valid_subplans, asyncplans))
+		return false;
+
+	/* Get valid async subplans. */
+	*valid_asyncplans = bms_intersect(asyncplans,
+									  *valid_subplans);
+
+	/* Adjust the valid subplans to contain sync subplans only. */
+	*valid_subplans = bms_del_members(*valid_subplans,
+									  *valid_asyncplans);
+	return true;
+}
+
 /* ----------------
  *	 RecursiveUnionState information
  *
diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h
index b523bcda8f3..fee491b77ad 100644
--- a/src/include/optimizer/cost.h
+++ b/src/include/optimizer/cost.h
@@ -70,6 +70,7 @@ extern PGDLLIMPORT bool enable_parallel_hash;
 extern PGDLLIMPORT bool enable_partition_pruning;
 extern PGDLLIMPORT bool enable_presorted_aggregate;
 extern PGDLLIMPORT bool enable_async_append;
+extern PGDLLIMPORT bool enable_async_merge_append;
 extern PGDLLIMPORT int constraint_exclusion;

---

From: Matheus Alcantara <[email-masked]>
Date: Mon, 17 Nov 2025 18:09:19 -0300

> (Merge)Append decides to insert Sort node.
Your explanation about why this change is needed that you've include on
your first email sounds more clear IMHO. I would suggest the following
for a commit message:
    mark_async_capable() believes that path corresponds to plan. This is
    not true when create_[merge_]append_plan() inserts sort node. In
    this case mark_async_capable() can treat Sort plan node as some
    other and crash. Fix this by handling the Sort node separately.

    This is needed to make MergeAppend node async-capable that it will
    be implemented in a next commit.

What do you think?

I was reading the patch changes again and I have a minor point:

                                /*
-                                * If the generated plan node includes
a gating Result node,
-                                * we can't execute it asynchronously.
+                                * If the generated plan node includes
a gating Result node or
+                                * a Sort node, we can't execute it
asynchronously.
                                 */
-                               if (IsA(plan, Result))
+                               if (IsA(plan, Result) || IsA(plan, Sort))

Shouldn't we cast the plan to SubqueryScan* after the IsA(...) check? I
know this code has been before your changes but type casting before a
IsA() check sounds a bit strange to me. Also perhaps we could add an
Assert(IsA(plan, SubqueryScan)) after the IsA(...) check and before the
type casting just for sanity?

> subplans, as subplans ordering matters, and we can't arbitrary switch
Ok, thanks for the explanation.

> last two states have meaning
I think that's ok to have these separated checks on nodeAppend.c and
nodeMergeAppend.c once the majority of duplicated steps that would be
required is centralized into a single reusable function.

I also agree that execnodes.h may not be the best place to declare this
function but I also don't have too many ideas of where to put it. Let's
see if we have more comments on this.

> new subplans in ExecMergeAppend(), we have to classify them.
Thanks, the code coverage looks better now.

I plan to do another round of review on 0002, in the meantime I'm
sharing these comments for now.

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 18 Nov 2025 10:14:23 +0300

Hi.

>     be implemented in a next commit.

Seems to be OK.

> type casting just for sanity?

Yes, checking for node not to be A and then using it as B seems to be 
strange. But casting to another type and checking if node is of a 
particular type before using seems to be rather common. It doesn't do 
any harm if we don't actually refer to SubqueryScan fields.

Updated the first patch.

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From 10d872ce10bc8c7f6a430fe70367714b526fab4d Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH 1/2] mark_async_capable(): subpath should match subplan

This is needed to make MergeAppend node async-capable that will
be implemented in a next commit.
---
 src/backend/optimizer/plan/createplan.c | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 8af091ba647..5cd7fa7b897 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1139,10 +1139,12 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
-				 * If the generated plan node includes a gating Result node,
-				 * we can't execute it asynchronously.
+				 * Check that plan is really a SubqueryScan before using it.
+				 * It can be not true, if the generated plan node includes a
+				 * gating Result node or a Sort node. In such case we can't
+				 * execute it asynchronously.
 				 */
-				if (IsA(plan, Result))
+				if (!IsA(scan_plan, SubqueryScan))
 					return false;
 
 				/*
@@ -1160,10 +1162,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
 
 				Assert(fdwroutine != NULL);
@@ -1176,9 +1178,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 
 			/*
-- 
2.43.0

From 76a212d1ba66cb727a95a4f6cba28786795b6d11 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH 2/2] MergeAppend should support Async Foreign Scan subplans

---

 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append

 
+-- Test Merge Append
 
+-- Test Merge Append

+-- Test Merge Append

 

 /*

 
 
 /*

 

+		/*

 
 		/*
 
 	return result;
@@ -355,6 +451,7 @@ void
 
 	/*

 typedef struct
 {
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 5cd7fa7b897..8a023aac33b 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1466,6 +1466,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
 	RelOptInfo *rel = best_path->path.parent;
+	bool		consider_async = false;
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1480,6 +1481,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->righttree = NULL;
 	node->apprelids = rel->relids;
 
@@ -1580,6 +1585,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 			subplan = sort_plan;
 		}

 
index f503d36b92e..ea014e006f2 100644

---

From: "Matheus Alcantara" <[email-masked]>
Date: Wed, 19 Nov 2025 18:51:35 -0300

> Updated the first patch.
Thanks for the new version. Some new comments.

v7-0002-MergeAppend-should-support-Async-Foreign-Scan-subpla.patch:

1. Should be "nasyncplans" instead of "nplans"? ExecInitAppend use
"nasyncplans" to allocate the as_asyncresults array.

2. I think that this comment should be updated. IIUC ms_valid_subplans
may not be all subplans because classify_matching_subplans() may move
async ones to ms_valid_asyncplans. Is that right?

/*
 * If we've yet to determine the valid subplans then do so now.  If
 * run-time pruning is disabled then the valid subplans will always be
 * set to all subplans.
 */

3. This code comment should also mention the Assert(!bms_is_member(...));?

4. It's worth include bms_num_members(node->ms_needrequest) <= 0 check
on ExecMergeAppendAsyncRequest() as an early return? IIUC it would avoid
the bms_is_member(), bms_next_member() and bms_is_empty(needrequest)
calls.

ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
        Bitmapset  *needrequest;
        int                     i;

+       if (bms_num_members(node->ms_needrequest) <= 0)
+               return false;
+

I'm attaching a diff with some cosmetic changes of indentation and
comments. Feel free to include on the patch or not.

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index c89e2d2787f..a2ed5f71a35 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1198,6 +1198,9 @@ classify_matching_subplans(AppendState *node)
 	}
 
 	/* No valid async subplans identified. */
-	if (!classify_matching_subplans_common(&node->as_valid_subplans, node->as_asyncplans, &node->as_valid_asyncplans))
+	if (!classify_matching_subplans_common(
+										   &node->as_valid_subplans,
+										   node->as_asyncplans,
+										   &node->as_valid_asyncplans))
 		node->as_nasyncremain = 0;
 }
diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c
index 7db41fbf40f..feb25a813b1 100644
--- a/src/backend/executor/nodeMergeAppend.c
+++ b/src/backend/executor/nodeMergeAppend.c
@@ -533,7 +533,10 @@ classify_matching_subplans(MergeAppendState *node)
 	}
 
 	/* No valid async subplans identified. */
-	if (!classify_matching_subplans_common(&node->ms_valid_subplans, node->ms_asyncplans, &node->ms_valid_asyncplans))
+	if (!classify_matching_subplans_common(
+										   &node->ms_valid_subplans,
+										   node->ms_asyncplans,
+										   &node->ms_valid_asyncplans))
 		node->ms_asyncremain = NULL;
 }
 
@@ -721,11 +724,14 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 	{
 		/* The ending subplan wouldn't have been pending for a callback. */
 		Assert(!areq->callback_pending);
-		node->ms_asyncremain = bms_del_member(node->ms_asyncremain, areq->request_index);
+		node->ms_asyncremain = bms_del_member(node->ms_asyncremain,
+											  areq->request_index);
 		return;
 	}
 
-	node->ms_has_asyncresults = bms_add_member(node->ms_has_asyncresults, areq->request_index);
+	/* Mark that the async request has a result */
+	node->ms_has_asyncresults = bms_add_member(node->ms_has_asyncresults,
+											   areq->request_index);
 	/* Save result so we can return it. */
 	node->ms_asyncresults[areq->request_index] = slot;
 
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 2bef54550a3..1dc7e9e6145 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1585,7 +1585,9 @@ GetNeedRequest(PlanState *ps)
 
 /* Common part of classify_matching_subplans() for Append and MergeAppend */
 static inline bool
-classify_matching_subplans_common(Bitmapset **valid_subplans, Bitmapset *asyncplans, Bitmapset **valid_asyncplans)
+classify_matching_subplans_common(Bitmapset **valid_subplans,
+								  Bitmapset *asyncplans,
+								  Bitmapset **valid_asyncplans)
 {
 	Assert(*valid_asyncplans == NULL);

---

From: Alexander Pyhalov <[email-masked]>
Date: Thu, 20 Nov 2025 17:22:32 +0300

> +			palloc0(nplans * sizeof(TupleTableSlot *));

No. There's a difference between how Append and MergeAppend handle async 
results.

When Append looks for the next result, it can return any of them.
So, async results are not ordered in Append.
We have maximum nasyncplans of async results and return the first 
available result
when we asked for one . For example, in ExecAppendAsyncRequest():

1004         /*
1005          * If there are any asynchronously-generated results that 
have not yet
1006          * been returned, we have nothing to do; just return one of 
them.
1007          */
1008         if (node->as_nasyncresults > 0)
1009         {
1010                 --node->as_nasyncresults;
1011                 *result = 
node->as_asyncresults[node->as_nasyncresults];
1012                 return true;
1013         }

ExecAppendAsyncGetNext() looks (via ExecAppendAsyncRequest()) on any 
result.

However, when we are asked for result in MergeAppend, we should return 
result of
the specific subplan. To achieve this we should know, which subplan 
given results correspond to.
So, we enumerate async results in the same way as requests (or 
ms_valid_asyncplans).
Look at ExecAppendAsyncGetNext()/ExecAppendAsyncRequest().

>  * run-time pruning is disabled then the valid subplans will always be

Yes, you are correct, and similar comment in nodeAppend.c lacks the last 
sentence.
Removed it.

> the bms_is_member(), bms_next_member() and bms_is_empty(needrequest)

We can't exclude the first bms_is_member(), as node->ms_needrequest can 
be empty
(we've already got result), so do not need to do request to get it, just
return previously fetched result.

Not sure about check above the following lines:

650         i = -1;
651         while ((i = bms_next_member(node->ms_needrequest, i)) >= 0)
652         {
653                 if (!bms_is_member(i, node->ms_has_asyncresults))
654                         needrequest = bms_add_member(needrequest, 
i);
655         }
656

I think, it shouldn't be much cheaper as bms_next_member() will execute 
a couple instructions
to find out that the number of words in bitmapset is zero, but will do 
nothing expensive.

> +       if (bms_num_members(node->ms_needrequest) <= 0)

No, as I've mentioned, we can't exclude bms_is_member(mplan, 
node->ms_has_asyncresults) check.
We could have received result while waiting for data for another 
subplan.

Let's assume, we have 2 async subplans (0 and 1). For example, we've 
decided
to get data from subplan 1. We 've already send requests to both async 
subplans (in ExecMergeAppendAsyncBegin() or later).
Now we do ExecMergeAppendAsyncRequest(), but there's no subplans, which 
need request.
So we enter the waiting loop. Let's assume we got event for another 
subplan (0). Via ExecAsyncNotify(),
ExecAsyncForeignScanNotify() we go to postgresForeignAsyncNotify(), 
fetch data and mark request as complete.
Via ExecAsyncMergeAppendResponse() we save results for subplan 0 in 
node->ms_asyncresults[0]. When we finally
got result for subplan 1, we do the same, but now exit the loop. When 
MergeAppend finally decides that it needs
results from subplan 0, we already have them, but ms_needrequest is 
empty, so  ExecMergeAppendAsyncRequest()
just returns this pre-fetched tuple.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From 07aa2f2e592625bec541c4296f77e424f7e662b1 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH 1/2] mark_async_capable(): subpath should match subplan

index 8af091ba647..478ae0b7ba1 100644
 
 				/*
+				if (!IsA(plan, SubqueryScan))
 					return false;
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.43.0

From a5f1755868312e836727ef58a2be7580f313c1a3 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH 2/2] MergeAppend should support Async Foreign Scan subplans

---
 .../postgres_fdw/expected/postgres_fdw.out    | 288 +++++++++++
 contrib/postgres_fdw/postgres_fdw.c           |  10 +-
 contrib/postgres_fdw/sql/postgres_fdw.sql     |  87 ++++
 doc/src/sgml/config.sgml                      |  14 +
 src/backend/executor/execAsync.c              |   4 +
 src/backend/executor/nodeAppend.c             |  24 +-
 src/backend/executor/nodeMergeAppend.c        | 471 +++++++++++++++++-
 src/backend/optimizer/path/costsize.c         |   1 +
 src/backend/optimizer/plan/createplan.c       |   9 +
 src/backend/utils/misc/guc_parameters.dat     |   8 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/executor/nodeMergeAppend.h        |   1 +
 src/include/nodes/execnodes.h                 |  59 +++
 src/include/optimizer/cost.h                  |   1 +
 src/test/regress/expected/sysviews.out        |   3 +-
 15 files changed, 951 insertions(+), 30 deletions(-)

 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append

 
+-- Test Merge Append
 
+-- Test Merge Append

+-- Test Merge Append

 

 /*
index a11b36c7176..a2ed5f71a35 100644
 
 	/* Nothing to do if there are no valid subplans. */
 	if (bms_is_empty(node->as_valid_subplans))
@@ -1200,21 +1197,10 @@ classify_matching_subplans(AppendState *node)
 		return;
 	}
 
index 405e8f94285..618b899e7fe 100644

 /*

 

+		/*

@@ -226,14 +296,18 @@ ExecMergeAppend(PlanState *pstate)
 		if (node->ms_nplans == 0)
 			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
 
-		/*
-		 * If we've yet to determine the valid subplans then do so now.  If
-		 * run-time pruning is disabled then the valid subplans will always be
-		 * set to all subplans.
-		 */
 
 		/*
@@ -246,6 +320,16 @@ ExecMergeAppend(PlanState *pstate)
@@ -260,7 +344,13 @@ ExecMergeAppend(PlanState *pstate)
@@ -276,6 +366,8 @@ ExecMergeAppend(PlanState *pstate)
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*
@@ -365,8 +458,11 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -387,6 +483,367 @@ ExecReScanMergeAppend(MergeAppendState *node)
+	/* We should handle previous async result prior to getting new one */
 
 typedef struct
 {
index 478ae0b7ba1..65667bc3698 100644
 
 	/*

 
 
index dc9e2255f8a..d949d2aad04 100644

index 18ae8f0d4bb..1dc7e9e6145 100644
@@ -1545,10 +1545,69 @@ typedef struct MergeAppendState

---

From: "Matheus Alcantara" <[email-masked]>
Date: Wed, 17 Dec 2025 17:01:31 -0300

Thanks for the new version. I don't have other comments on the current
state of the patch. It seems to working as expected and we have
performance improvements that I think that it make it worthwhile.

I have just a small comment on 0002:

Should we use the same WAIT_EVENT_APPEND_READY or create a new wait
event for merge append?

I've spent some time thinking about how we could remove some parts of
the duplicated code that you've previously mention. I think that we
could try to create something like we already have for relation scan
operations, that we have execScan.c that is used for example by
nodeSeqScan.c and nodeIndexScan.c. The attached patch 0003 is a draft
that I attempt to implement this idea. The 0001 and 0002 remains the
same as the previous version. The 0003 was build on top of these.

I've created Appender and AppenderState types that are used by
Append/MergeAppend and AppendState/MergeAppendState respectively (I
should have think in a better name for these base type, ideas are
welcome). The execAppend.c was created to have the functions that can be
reused by Append and MergeAppend execution. I've tried to remove
duplicated code blocks that was almost the same and that didn't require
much refactoring.

I think that there still more opportunities to remove similar code
blocks that for example are on ExecMergeAppendAsyncGetNext and
ExecAppendAsyncGetNext but it require refactoring.

Thoughts?

From e07a1c8a6c6f02c08e65070a5c4ff962dd3bc861 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH v9 1/3] mark_async_capable(): subpath should match subplan

index bc417f93840..84f60c48653 100644
 
 				/*
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.51.2

From 85066dccdd9215663d960c0284c9f5e2b232159b Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH v9 2/3] MergeAppend should support Async Foreign Scan subplans

---

index 48e3185b227..e2240d34d21 100644
 
 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append
index 5e178c21b39..bd551a1db72 100644

 
+-- Test Merge Append
 
+-- Test Merge Append

+-- Test Merge Append

 
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 405c9689bd0..165a5a5962e 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5461,6 +5461,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>

 /*
index 77c4dd9e4b1..dfbc7b510c4 100644

index 300bcd5cf33..f1c267eb9eb 100644

 /*

 

+		/*

 
-		/*
 
 		/*
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*
 
index a39cc793b4d..017e5977369 100644
 
 typedef struct
 {
index 84f60c48653..24325d42f0d 100644
 
 	/*

 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 3b9d8349078..bdb8fc1b3ad 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -812,6 +812,14 @@
   boot_val => 'true',
 },

 
index 3968429f991..5887cbf4f16 100644

index 0411db832f1..194b1f95289 100644
 
2.51.2

From 3a6ccb18a97bce531b0c16eb0db48ef182bdc0ad Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 16 Dec 2025 16:32:14 -0300
Subject: [PATCH v9 3/3] Create execAppend.c to avoid duplicated code on
 [Merge]Append

---
 contrib/pg_overexplain/pg_overexplain.c |   4 +-
 contrib/postgres_fdw/postgres_fdw.c     |   8 +-
 src/backend/commands/explain.c          |  26 +-
 src/backend/executor/Makefile           |   1 +
 src/backend/executor/execAmi.c          |   2 +-
 src/backend/executor/execAppend.c       | 409 +++++++++++++++++++
 src/backend/executor/execCurrent.c      |   4 +-
 src/backend/executor/execProcnode.c     |   8 +-
 src/backend/executor/meson.build        |   1 +
 src/backend/executor/nodeAppend.c       | 498 +++++-------------------
 src/backend/executor/nodeMergeAppend.c  | 417 +++-----------------
 src/backend/nodes/nodeFuncs.c           |   8 +-
 src/backend/optimizer/plan/createplan.c |  34 +-
 src/backend/optimizer/plan/setrefs.c    |  44 +--
 src/backend/optimizer/plan/subselect.c  |   4 +-
 src/backend/utils/adt/ruleutils.c       |   8 +-
 src/include/executor/execAppend.h       |  33 ++
 src/include/nodes/execnodes.h           |  80 ++--
 src/include/nodes/plannodes.h           |  45 +--
 19 files changed, 721 insertions(+), 913 deletions(-)
 create mode 100644 src/backend/executor/execAppend.c
 create mode 100644 src/include/executor/execAppend.h

diff --git a/contrib/pg_overexplain/pg_overexplain.c b/contrib/pg_overexplain/pg_overexplain.c
index fcdc17012da..7f18c2ab06c 100644
--- a/contrib/pg_overexplain/pg_overexplain.c
+++ b/contrib/pg_overexplain/pg_overexplain.c
@@ -228,12 +228,12 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
 				break;
 			case T_Append:
 				overexplain_bitmapset("Append RTIs",
-									  ((Append *) plan)->apprelids,
+									  ((Append *) plan)->ap.apprelids,
 									  es);
 				break;
 			case T_MergeAppend:
 				overexplain_bitmapset("Append RTIs",
-									  ((MergeAppend *) plan)->apprelids,
+									  ((MergeAppend *) plan)->ap.apprelids,
 									  es);
 				break;
 			case T_Result:
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index bd551a1db72..b01ad40ad17 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -2412,8 +2412,8 @@ find_modifytable_subplan(PlannerInfo *root,
 	{
 		Append	   *appendplan = (Append *) subplan;
 
-		if (subplan_index < list_length(appendplan->appendplans))
-			subplan = (Plan *) list_nth(appendplan->appendplans, subplan_index);
+		if (subplan_index < list_length(appendplan->ap.subplans))
+			subplan = (Plan *) list_nth(appendplan->ap.subplans, subplan_index);
 	}
 	else if (IsA(subplan, Result) &&
 			 outerPlan(subplan) != NULL &&
@@ -2421,8 +2421,8 @@ find_modifytable_subplan(PlannerInfo *root,
 	{
 		Append	   *appendplan = (Append *) outerPlan(subplan);
 
-		if (subplan_index < list_length(appendplan->appendplans))
-			subplan = (Plan *) list_nth(appendplan->appendplans, subplan_index);
+		if (subplan_index < list_length(appendplan->ap.subplans))
+			subplan = (Plan *) list_nth(appendplan->ap.subplans, subplan_index);
 	}
 
 	/* Now, have we got a ForeignScan on the desired rel? */
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index 5a6390631eb..3eaa1f7459e 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -1224,11 +1224,11 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
 			break;
 		case T_Append:
 			*rels_used = bms_add_members(*rels_used,
-										 ((Append *) plan)->apprelids);
+										 ((Append *) plan)->ap.apprelids);
 			break;
 		case T_MergeAppend:
 			*rels_used = bms_add_members(*rels_used,
-										 ((MergeAppend *) plan)->apprelids);
+										 ((MergeAppend *) plan)->ap.apprelids);
 			break;
 		case T_Result:
 			*rels_used = bms_add_members(*rels_used,
@@ -1272,7 +1272,7 @@ plan_is_disabled(Plan *plan)
 		 * includes any run-time pruned children.  Ignoring those could give
 		 * us the incorrect number of disabled nodes.
 		 */
-		foreach(lc, aplan->appendplans)
+		foreach(lc, aplan->ap.subplans)
 		{
 			Plan	   *subplan = lfirst(lc);
 
@@ -1289,7 +1289,7 @@ plan_is_disabled(Plan *plan)
 		 * includes any run-time pruned children.  Ignoring those could give
 		 * us the incorrect number of disabled nodes.
 		 */
-		foreach(lc, maplan->mergeplans)
+		foreach(lc, maplan->ap.subplans)
 		{
 			Plan	   *subplan = lfirst(lc);
 
@@ -2336,13 +2336,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_Append:
-			ExplainMissingMembers(((AppendState *) planstate)->as_nplans,
-								  list_length(((Append *) plan)->appendplans),
+			ExplainMissingMembers(((AppendState *) planstate)->as.nplans,
+								  list_length(((Append *) plan)->ap.subplans),
 								  es);
 			break;
 		case T_MergeAppend:
-			ExplainMissingMembers(((MergeAppendState *) planstate)->ms_nplans,
-								  list_length(((MergeAppend *) plan)->mergeplans),
+			ExplainMissingMembers(((MergeAppendState *) planstate)->ms.nplans,
+								  list_length(((MergeAppend *) plan)->ap.subplans),
 								  es);
 			break;
 		default:
@@ -2386,13 +2386,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_Append:
-			ExplainMemberNodes(((AppendState *) planstate)->appendplans,
-							   ((AppendState *) planstate)->as_nplans,
+			ExplainMemberNodes(((AppendState *) planstate)->as.plans,
+							   ((AppendState *) planstate)->as.nplans,
 							   ancestors, es);
 			break;
 		case T_MergeAppend:
-			ExplainMemberNodes(((MergeAppendState *) planstate)->mergeplans,
-							   ((MergeAppendState *) planstate)->ms_nplans,
+			ExplainMemberNodes(((MergeAppendState *) planstate)->ms.plans,
+							   ((MergeAppendState *) planstate)->ms.nplans,
 							   ancestors, es);
 			break;
 		case T_BitmapAnd:
@@ -2606,7 +2606,7 @@ static void
 show_merge_append_keys(MergeAppendState *mstate, List *ancestors,
 					   ExplainState *es)
 {
-	MergeAppend *plan = (MergeAppend *) mstate->ps.plan;
+	MergeAppend *plan = (MergeAppend *) mstate->ms.ps.plan;
 
 	show_sort_group_keys((PlanState *) mstate, "Sort Key",
 						 plan->numCols, 0, plan->sortColIdx,
diff --git a/src/backend/executor/Makefile b/src/backend/executor/Makefile
index 11118d0ce02..66b62fca921 100644
--- a/src/backend/executor/Makefile
+++ b/src/backend/executor/Makefile
@@ -15,6 +15,7 @@ include $(top_builddir)/src/Makefile.global
 OBJS = \
 	execAmi.o \
 	execAsync.o \
+	execAppend.o \
 	execCurrent.o \
 	execExpr.o \
 	execExprInterp.o \
diff --git a/src/backend/executor/execAmi.c b/src/backend/executor/execAmi.c
index 1d0e8ad57b4..5c897048ba3 100644
--- a/src/backend/executor/execAmi.c
+++ b/src/backend/executor/execAmi.c
@@ -537,7 +537,7 @@ ExecSupportsBackwardScan(Plan *node)
 				if (((Append *) node)->nasyncplans > 0)
 					return false;
 
-				foreach(l, ((Append *) node)->appendplans)
+				foreach(l, ((Append *) node)->ap.subplans)
 				{
 					if (!ExecSupportsBackwardScan((Plan *) lfirst(l)))
 						return false;
diff --git a/src/backend/executor/execAppend.c b/src/backend/executor/execAppend.c
new file mode 100644
index 00000000000..624fb207882
--- /dev/null
+++ b/src/backend/executor/execAppend.c
@@ -0,0 +1,409 @@
+/*-------------------------------------------------------------------------
+ *
+ * execAppend.c
+ *	  This code provides support functions for executing MergeAppend and Append
+ *	  nodes.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *	  src/backend/executor/execAppend.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+#include "executor/executor.h"
+#include "executor/execAppend.h"
+#include "executor/execAsync.h"
+#include "executor/execPartition.h"
+#include "storage/latch.h"
+#include "storage/waiteventset.h"
+#include "miscadmin.h"
+
+#define EVENT_BUFFER_SIZE			16
+
+void
+ExecInitAppender(AppenderState * state,
+							 Appender * node,
+							 EState *estate,
+							 int eflags,
+							 int first_partial_plan,
+							 int *first_valid_partial_plan)
+{
+	PlanState **appendplanstates;
+	const TupleTableSlotOps *appendops;
+	Bitmapset  *validsubplans;
+	Bitmapset  *asyncplans;
+	int			nplans;
+	int			nasyncplans;
+	int			firstvalid;
+	int			i,
+				j;
+
+	/* If run-time partition pruning is enabled, then set that up now */
+	if (node->part_prune_index >= 0)
+	{
+		PartitionPruneState *prunestate;
+
+		/*
+		 * Set up pruning data structure.  This also initializes the set of
+		 * subplans to initialize (validsubplans) by taking into account the
+		 * result of performing initial pruning if any.
+		 */
+		prunestate = ExecInitPartitionExecPruning(&state->ps,
+												  list_length(node->subplans),
+												  node->part_prune_index,
+												  node->apprelids,
+												  &validsubplans);
+		state->prune_state = prunestate;
+		nplans = bms_num_members(validsubplans);
+
+		/*
+		 * When no run-time pruning is required and there's at least one
+		 * subplan, we can fill as_valid_subplans immediately, preventing
+		 * later calls to ExecFindMatchingSubPlans.
+		 */
+		if (!prunestate->do_exec_prune && nplans > 0)
+		{
+			state->valid_subplans = bms_add_range(NULL, 0, nplans - 1);
+			state->valid_subplans_identified = true;
+		}
+	}
+	else
+	{
+		nplans = list_length(node->subplans);
+
+		/*
+		 * When run-time partition pruning is not enabled we can just mark all
+		 * subplans as valid; they must also all be initialized.
+		 */
+		Assert(nplans > 0);
+		state->valid_subplans = validsubplans =
+			bms_add_range(NULL, 0, nplans - 1);
+		state->valid_subplans_identified = true;
+		state->prune_state = NULL;
+	}
+
+	appendplanstates = (PlanState **) palloc(nplans * sizeof(PlanState *));
+
+	/*
+	 * call ExecInitNode on each of the valid plans to be executed and save
+	 * the results into the appendplanstates array.
+	 *
+	 * While at it, find out the first valid partial plan.
+	 */
+	j = 0;
+	asyncplans = NULL;
+	nasyncplans = 0;
+	firstvalid = nplans;
+	i = -1;
+	while ((i = bms_next_member(validsubplans, i)) >= 0)
+	{
+		Plan	   *initNode = (Plan *) list_nth(node->subplans, i);
+
+		/*
+		 * Record async subplans.  When executing EvalPlanQual, we treat them
+		 * as sync ones; don't do this when initializing an EvalPlanQual plan
+		 * tree.
+		 */
+		if (initNode->async_capable && estate->es_epq_active == NULL)
+		{
+			asyncplans = bms_add_member(asyncplans, j);
+			nasyncplans++;
+		}
+
+		/*
+		 * Record the lowest appendplans index which is a valid partial plan.
+		 */
+		if (first_valid_partial_plan && i >= first_partial_plan && j < firstvalid)
+			firstvalid = j;
+
+		appendplanstates[j++] = ExecInitNode(initNode, estate, eflags);
+	}
+
+	if (first_valid_partial_plan)
+		*first_valid_partial_plan = firstvalid;
+
+	state->plans = appendplanstates;
+	state->nplans = nplans;
+
+	/*
+	 * Initialize Append's result tuple type and slot.  If the child plans all
+	 * produce the same fixed slot type, we can use that slot type; otherwise
+	 * make a virtual slot.  (Note that the result slot itself is used only to
+	 * return a null tuple at end of execution; real tuples are returned to
+	 * the caller in the children's own result slots.  What we are doing here
+	 * is allowing the parent plan node to optimize if the Append will return
+	 * only one kind of slot.)
+	 */
+	appendops = ExecGetCommonSlotOps(appendplanstates, j);
+	if (appendops != NULL)
+	{
+		ExecInitResultTupleSlotTL(&state->ps, appendops);
+	}
+	else
+	{
+		ExecInitResultTupleSlotTL(&state->ps, &TTSOpsVirtual);
+		/* show that the output slot type is not fixed */
+		state->ps.resultopsset = true;
+		state->ps.resultopsfixed = false;
+	}
+
+	/* Initialize async state */
+	state->asyncplans = asyncplans;
+	state->nasyncplans = nasyncplans;
+	state->asyncrequests = NULL;
+	state->asyncresults = NULL;
+	state->needrequest = NULL;
+	state->eventset = NULL;
+	state->valid_asyncplans = NULL;
+
+	if (nasyncplans > 0)
+	{
+		state->asyncrequests = (AsyncRequest **)
+			palloc0(nplans * sizeof(AsyncRequest *));
+
+		i = -1;
+		while ((i = bms_next_member(asyncplans, i)) >= 0)
+		{
+			AsyncRequest *areq;
+
+			areq = palloc_object(AsyncRequest);
+			areq->requestor = (PlanState *) state;
+			areq->requestee = appendplanstates[i];
+			areq->request_index = i;
+			areq->callback_pending = false;
+			areq->request_complete = false;
+			areq->result = NULL;
+
+			state->asyncrequests[i] = areq;
+		}
+
+		/*
+		 * AppendState and MergeAppendState have slightly different allocation
+		 * sizes for asyncresults in the original code, but we unify to the
+		 * larger requirement or specific nplans if required.
+		 */
+		state->asyncresults = (TupleTableSlot **)
+			palloc0(nplans * sizeof(TupleTableSlot *));
+	}
+
+	/*
+	 * Miscellaneous initialization
+	 */
+	state->ps.ps_ProjInfo = NULL;
+}
+
+void
+ExecReScanAppender(AppenderState *node)
+{
+	int			i;
+	int			nasyncplans = node->nasyncplans;
+
+	/*
+	 * If any PARAM_EXEC Params used in pruning expressions have changed, then
+	 * we'd better unset the valid subplans so that they are reselected for
+	 * the new parameter values.
+	 */
+	if (node->prune_state &&
+		bms_overlap(node->ps.chgParam,
+					node->prune_state->execparamids))
+	{
+		node->valid_subplans_identified = false;
+		bms_free(node->valid_subplans);
+		node->valid_subplans = NULL;
+		bms_free(node->valid_asyncplans);
+		node->valid_asyncplans = NULL;
+	}
+
+	for (i = 0; i < node->nplans; i++)
+	{
+		PlanState  *subnode = node->plans[i];
+
+		/*
+		 * ExecReScan doesn't know about my subplans, so I have to do
+		 * changed-parameter signaling myself.
+		 */
+		if (node->ps.chgParam != NULL)
+			UpdateChangedParamSet(subnode, node->ps.chgParam);
+
+		/*
+		 * If chgParam of subnode is not null then plan will be re-scanned by
+		 * first ExecProcNode.
+		 */
+		if (subnode->chgParam == NULL)
+			ExecReScan(subnode);
+	}
+
+	/* Reset async state */
+	if (nasyncplans > 0)
+	{
+		i = -1;
+		while ((i = bms_next_member(node->asyncplans, i)) >= 0)
+		{
+			AsyncRequest *areq = node->asyncrequests[i];
+
+			areq->callback_pending = false;
+			areq->request_complete = false;
+			areq->result = NULL;
+		}
+
+		node->needrequest = NULL;
+	}
+}
+
+void
+ExecAppenderAsyncEventWait(AppenderState * node, int timeout, uint32 wait_event_info)
+{
+	int			nevents = node->nasyncplans + 2; /* one for PM death and
+													 * one for latch */
+	int			noccurred;
+	int i;
+	WaitEvent	occurred_event[EVENT_BUFFER_SIZE];
+
+	Assert(node->eventset == NULL);
+
+	node->eventset = CreateWaitEventSet(CurrentResourceOwner, nevents);
+	AddWaitEventToSet(node->eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
+					  NULL, NULL);
+
+	/* Give each waiting subplan a chance to add an event. */
+	i = -1;
+	while ((i = bms_next_member(node->asyncplans, i)) >= 0)
+	{
+		AsyncRequest *areq = node->asyncrequests[i];
+
+		if (areq->callback_pending)
+			ExecAsyncConfigureWait(areq);
+	}
+
+	/*
+	 * No need for further processing if none of the subplans configured any
+	 * events.
+	 */
+	if (GetNumRegisteredWaitEvents(node->eventset) == 1)
+	{
+		FreeWaitEventSet(node->eventset);
+		node->eventset = NULL;
+		return;
+	}
+
+	/*
+	 * Add the process latch to the set, so that we wake up to process the
+	 * standard interrupts with CHECK_FOR_INTERRUPTS().
+	 *
+	 * NOTE: For historical reasons, it's important that this is added to the
+	 * WaitEventSet after the ExecAsyncConfigureWait() calls.  Namely,
+	 * postgres_fdw calls "GetNumRegisteredWaitEvents(set) == 1" to check if
+	 * any other events are in the set.  That's a poor design, it's
+	 * questionable for postgres_fdw to be doing that in the first place, but
+	 * we cannot change it now.  The pattern has possibly been copied to other
+	 * extensions too.
+	 */
+	AddWaitEventToSet(node->eventset, WL_LATCH_SET, PGINVALID_SOCKET,
+					  MyLatch, NULL);
+
+	/* Return at most EVENT_BUFFER_SIZE events in one call. */
+	if (nevents > EVENT_BUFFER_SIZE)
+		nevents = EVENT_BUFFER_SIZE;
+
+	/*
+	 * Wait until at least one event occurs.
+	 *
+	 * XXX: Make timeout and wait event configured
+	 */
+	noccurred = WaitEventSetWait(node->eventset, timeout , occurred_event,
+								 nevents, wait_event_info);
+
+
+	FreeWaitEventSet(node->eventset);
+	node->eventset = NULL;
+	if (noccurred == 0)
+		return;
+
+
+	/* Deliver notifications. */
+	for (i = 0; i < noccurred; i++)
+	{
+		WaitEvent  *w = &occurred_event[i];
+
+		/*
+		 * Each waiting subplan should have registered its wait event with
+		 * user_data pointing back to its AsyncRequest.
+		 */
+		if ((w->events & WL_SOCKET_READABLE) != 0)
+		{
+			AsyncRequest *areq = (AsyncRequest *) w->user_data;
+
+			if (areq->callback_pending)
+			{
+				/*
+				 * Mark it as no longer needing a callback.  We must do this
+				 * before dispatching the callback in case the callback resets
+				 * the flag.
+				 */
+				areq->callback_pending = false;
+
+				/* Do the actual work. */
+				ExecAsyncNotify(areq);
+			}
+		}
+
+		/* Handle standard interrupts */
+		if ((w->events & WL_LATCH_SET) != 0)
+		{
+			ResetLatch(MyLatch);
+			CHECK_FOR_INTERRUPTS();
+		}
+	}
+}
+
+void
+ExecAppenderAsyncBegin(AppenderState * node)
+{
+	int			i;
+
+	/* Backward scan is not supported by async-aware Appends. */
+	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+
+	/* We should never be called when there are no subplans */
+	Assert(node->nplans > 0);
+
+	/* We should never be called when there are no async subplans. */
+	Assert(node->nasyncplans > 0);
+
+	/* Make a request for each of the valid async subplans. */
+	i = -1;
+	while ((i = bms_next_member(node->valid_asyncplans, i)) >= 0)
+	{
+		AsyncRequest *areq = node->asyncrequests[i];
+
+		Assert(areq->request_index == i);
+		Assert(!areq->callback_pending);
+
+		/* Do the actual work. */
+		ExecAsyncRequest(areq);
+	}
+}
+
+void
+ExecEndAppender(AppenderState *node)
+{
+	PlanState **mergeplans;
+	int			nplans;
+	int			i;
+
+	/*
+	 * get information from the node
+	 */
+	mergeplans = node->plans;
+	nplans = node->nplans;
+
+	/*
+	 * shut down each of the subscans
+	 */
+	for (i = 0; i < nplans; i++)
+		ExecEndNode(mergeplans[i]);
+}
diff --git a/src/backend/executor/execCurrent.c b/src/backend/executor/execCurrent.c
index 3bfdc0230ff..e8cf2ead8a8 100644
--- a/src/backend/executor/execCurrent.c
+++ b/src/backend/executor/execCurrent.c
@@ -375,9 +375,9 @@ search_plan_tree(PlanState *node, Oid table_oid,
 				AppendState *astate = (AppendState *) node;
 				int			i;
 
-				for (i = 0; i < astate->as_nplans; i++)
+				for (i = 0; i < astate->as.nplans; i++)
 				{
-					ScanState  *elem = search_plan_tree(astate->appendplans[i],
+					ScanState  *elem = search_plan_tree(astate->as.plans[i],
 														table_oid,
 														pending_rescan);
 
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index f5f9cfbeead..3eb1de1cd30 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -910,8 +910,8 @@ ExecSetTupleBound(int64 tuples_needed, PlanState *child_node)
 		AppendState *aState = (AppendState *) child_node;
 		int			i;
 
-		for (i = 0; i < aState->as_nplans; i++)
-			ExecSetTupleBound(tuples_needed, aState->appendplans[i]);
+		for (i = 0; i < aState->as.nplans; i++)
+			ExecSetTupleBound(tuples_needed, aState->as.plans[i]);
 	}
 	else if (IsA(child_node, MergeAppendState))
 	{
@@ -923,8 +923,8 @@ ExecSetTupleBound(int64 tuples_needed, PlanState *child_node)
 		MergeAppendState *maState = (MergeAppendState *) child_node;
 		int			i;
 
-		for (i = 0; i < maState->ms_nplans; i++)
-			ExecSetTupleBound(tuples_needed, maState->mergeplans[i]);
+		for (i = 0; i < maState->ms.nplans; i++)
+			ExecSetTupleBound(tuples_needed, maState->ms.plans[i]);
 	}
 	else if (IsA(child_node, ResultState))
 	{
diff --git a/src/backend/executor/meson.build b/src/backend/executor/meson.build
index 2cea41f8771..b5cb710a59f 100644
--- a/src/backend/executor/meson.build
+++ b/src/backend/executor/meson.build
@@ -3,6 +3,7 @@
 backend_sources += files(
   'execAmi.c',
   'execAsync.c',
+  'execAppend.c',
   'execCurrent.c',
   'execExpr.c',
   'execExprInterp.c',
diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index dfbc7b510c4..873e4cb559e 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -57,13 +57,13 @@
 
 #include "postgres.h"
 
+#include "executor/execAppend.h"
 #include "executor/execAsync.h"
 #include "executor/execPartition.h"
 #include "executor/executor.h"
 #include "executor/nodeAppend.h"
 #include "miscadmin.h"
 #include "pgstat.h"
-#include "storage/latch.h"
 
 /* Shared state for parallel-aware Append. */
 struct ParallelAppendState
@@ -109,15 +109,6 @@ AppendState *
 ExecInitAppend(Append *node, EState *estate, int eflags)
 {
 	AppendState *appendstate = makeNode(AppendState);
-	PlanState **appendplanstates;
-	const TupleTableSlotOps *appendops;
-	Bitmapset  *validsubplans;
-	Bitmapset  *asyncplans;
-	int			nplans;
-	int			nasyncplans;
-	int			firstvalid;
-	int			i,
-				j;
 
 	/* check for unsupported flags */
 	Assert(!(eflags & EXEC_FLAG_MARK));
@@ -125,167 +116,27 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 	/*
 	 * create new AppendState for our append node
 	 */
-	appendstate->ps.plan = (Plan *) node;
-	appendstate->ps.state = estate;
-	appendstate->ps.ExecProcNode = ExecAppend;
+	appendstate->as.ps.plan = (Plan *) node;
+	appendstate->as.ps.state = estate;
+	appendstate->as.ps.ExecProcNode = ExecAppend;
 
 	/* Let choose_next_subplan_* function handle setting the first subplan */
 	appendstate->as_whichplan = INVALID_SUBPLAN_INDEX;
 	appendstate->as_syncdone = false;
 	appendstate->as_begun = false;
 
-	/* If run-time partition pruning is enabled, then set that up now */
-	if (node->part_prune_index >= 0)
-	{
-		PartitionPruneState *prunestate;
-
-		/*
-		 * Set up pruning data structure.  This also initializes the set of
-		 * subplans to initialize (validsubplans) by taking into account the
-		 * result of performing initial pruning if any.
-		 */
-		prunestate = ExecInitPartitionExecPruning(&appendstate->ps,
-												  list_length(node->appendplans),
-												  node->part_prune_index,
-												  node->apprelids,
-												  &validsubplans);
-		appendstate->as_prune_state = prunestate;
-		nplans = bms_num_members(validsubplans);
-
-		/*
-		 * When no run-time pruning is required and there's at least one
-		 * subplan, we can fill as_valid_subplans immediately, preventing
-		 * later calls to ExecFindMatchingSubPlans.
-		 */
-		if (!prunestate->do_exec_prune && nplans > 0)
-		{
-			appendstate->as_valid_subplans = bms_add_range(NULL, 0, nplans - 1);
-			appendstate->as_valid_subplans_identified = true;
-		}
-	}
-	else
-	{
-		nplans = list_length(node->appendplans);
-
-		/*
-		 * When run-time partition pruning is not enabled we can just mark all
-		 * subplans as valid; they must also all be initialized.
-		 */
-		Assert(nplans > 0);
-		appendstate->as_valid_subplans = validsubplans =
-			bms_add_range(NULL, 0, nplans - 1);
-		appendstate->as_valid_subplans_identified = true;
-		appendstate->as_prune_state = NULL;
-	}
-
-	appendplanstates = (PlanState **) palloc(nplans *
-											 sizeof(PlanState *));
-
-	/*
-	 * call ExecInitNode on each of the valid plans to be executed and save
-	 * the results into the appendplanstates array.
-	 *
-	 * While at it, find out the first valid partial plan.
-	 */
-	j = 0;
-	asyncplans = NULL;
-	nasyncplans = 0;
-	firstvalid = nplans;
-	i = -1;
-	while ((i = bms_next_member(validsubplans, i)) >= 0)
-	{
-		Plan	   *initNode = (Plan *) list_nth(node->appendplans, i);
-
-		/*
-		 * Record async subplans.  When executing EvalPlanQual, we treat them
-		 * as sync ones; don't do this when initializing an EvalPlanQual plan
-		 * tree.
-		 */
-		if (initNode->async_capable && estate->es_epq_active == NULL)
-		{
-			asyncplans = bms_add_member(asyncplans, j);
-			nasyncplans++;
-		}
-
-		/*
-		 * Record the lowest appendplans index which is a valid partial plan.
-		 */
-		if (i >= node->first_partial_plan && j < firstvalid)
-			firstvalid = j;
-
-		appendplanstates[j++] = ExecInitNode(initNode, estate, eflags);
-	}
-
-	appendstate->as_first_partial_plan = firstvalid;
-	appendstate->appendplans = appendplanstates;
-	appendstate->as_nplans = nplans;
+	/* Initialize common fields */
+	ExecInitAppender(&appendstate->as,
+					 &node->ap,
+					 estate,
+					 eflags,
+					 node->first_partial_plan,
+					 &appendstate->as_first_partial_plan);
 
-	/*
-	 * Initialize Append's result tuple type and slot.  If the child plans all
-	 * produce the same fixed slot type, we can use that slot type; otherwise
-	 * make a virtual slot.  (Note that the result slot itself is used only to
-	 * return a null tuple at end of execution; real tuples are returned to
-	 * the caller in the children's own result slots.  What we are doing here
-	 * is allowing the parent plan node to optimize if the Append will return
-	 * only one kind of slot.)
-	 */
-	appendops = ExecGetCommonSlotOps(appendplanstates, j);
-	if (appendops != NULL)
-	{
-		ExecInitResultTupleSlotTL(&appendstate->ps, appendops);
-	}
-	else
-	{
-		ExecInitResultTupleSlotTL(&appendstate->ps, &TTSOpsVirtual);
-		/* show that the output slot type is not fixed */
-		appendstate->ps.resultopsset = true;
-		appendstate->ps.resultopsfixed = false;
-	}
+	if (appendstate->as.nasyncplans > 0 && appendstate->as.valid_subplans_identified)
+		classify_matching_subplans(appendstate);
 
-	/* Initialize async state */
-	appendstate->as_asyncplans = asyncplans;
-	appendstate->as_nasyncplans = nasyncplans;
-	appendstate->as_asyncrequests = NULL;
-	appendstate->as_asyncresults = NULL;
-	appendstate->as_nasyncresults = 0;
 	appendstate->as_nasyncremain = 0;
-	appendstate->as_needrequest = NULL;
-	appendstate->as_eventset = NULL;
-	appendstate->as_valid_asyncplans = NULL;
-
-	if (nasyncplans > 0)
-	{
-		appendstate->as_asyncrequests = (AsyncRequest **)
-			palloc0(nplans * sizeof(AsyncRequest *));
-
-		i = -1;
-		while ((i = bms_next_member(asyncplans, i)) >= 0)
-		{
-			AsyncRequest *areq;
-
-			areq = palloc_object(AsyncRequest);
-			areq->requestor = (PlanState *) appendstate;
-			areq->requestee = appendplanstates[i];
-			areq->request_index = i;
-			areq->callback_pending = false;
-			areq->request_complete = false;
-			areq->result = NULL;
-
-			appendstate->as_asyncrequests[i] = areq;
-		}
-
-		appendstate->as_asyncresults = (TupleTableSlot **)
-			palloc0(nasyncplans * sizeof(TupleTableSlot *));
-
-		if (appendstate->as_valid_subplans_identified)
-			classify_matching_subplans(appendstate);
-	}
-
-	/*
-	 * Miscellaneous initialization
-	 */
-
-	appendstate->ps.ps_ProjInfo = NULL;
 
 	/* For parallel query, this will be overridden later. */
 	appendstate->choose_next_subplan = choose_next_subplan_locally;
@@ -315,11 +166,11 @@ ExecAppend(PlanState *pstate)
 		Assert(!node->as_syncdone);
 
 		/* Nothing to do if there are no subplans */
-		if (node->as_nplans == 0)
-			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+		if (node->as.nplans == 0)
+			return ExecClearTuple(node->as.ps.ps_ResultTupleSlot);
 
 		/* If there are any async subplans, begin executing them. */
-		if (node->as_nasyncplans > 0)
+		if (node->as.nasyncplans > 0)
 			ExecAppendAsyncBegin(node);
 
 		/*
@@ -327,11 +178,11 @@ ExecAppend(PlanState *pstate)
 		 * proceeding.
 		 */
 		if (!node->choose_next_subplan(node) && node->as_nasyncremain == 0)
-			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+			return ExecClearTuple(node->as.ps.ps_ResultTupleSlot);
 
 		Assert(node->as_syncdone ||
 			   (node->as_whichplan >= 0 &&
-				node->as_whichplan < node->as_nplans));
+				node->as_whichplan < node->as.nplans));
 
 		/* And we're initialized. */
 		node->as_begun = true;
@@ -346,19 +197,19 @@ ExecAppend(PlanState *pstate)
 		/*
 		 * try to get a tuple from an async subplan if any
 		 */
-		if (node->as_syncdone || !bms_is_empty(node->as_needrequest))
+		if (node->as_syncdone || !bms_is_empty(node->as.needrequest))
 		{
 			if (ExecAppendAsyncGetNext(node, &result))
 				return result;
 			Assert(!node->as_syncdone);
-			Assert(bms_is_empty(node->as_needrequest));
+			Assert(bms_is_empty(node->as.needrequest));
 		}
 
 		/*
 		 * figure out which sync subplan we are currently processing
 		 */
-		Assert(node->as_whichplan >= 0 && node->as_whichplan < node->as_nplans);
-		subnode = node->appendplans[node->as_whichplan];
+		Assert(node->as_whichplan >= 0 && node->as_whichplan < node->as.nplans);
+		subnode = node->as.plans[node->as_whichplan];
 
 		/*
 		 * get a tuple from the subplan
@@ -385,7 +236,7 @@ ExecAppend(PlanState *pstate)
 
 		/* choose new sync subplan; if no sync/async subplans, we're done */
 		if (!node->choose_next_subplan(node) && node->as_nasyncremain == 0)
-			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+			return ExecClearTuple(node->as.ps.ps_ResultTupleSlot);
 	}
 }
 
@@ -400,81 +251,23 @@ ExecAppend(PlanState *pstate)
 void
 ExecEndAppend(AppendState *node)
 {
-	PlanState **appendplans;
-	int			nplans;
-	int			i;
-
-	/*
-	 * get information from the node
-	 */
-	appendplans = node->appendplans;
-	nplans = node->as_nplans;
-
-	/*
-	 * shut down each of the subscans
-	 */
-	for (i = 0; i < nplans; i++)
-		ExecEndNode(appendplans[i]);
+	ExecEndAppender(&node->as);
 }
 
 void
 ExecReScanAppend(AppendState *node)
 {
-	int			nasyncplans = node->as_nasyncplans;
-	int			i;
-
-	/*
-	 * If any PARAM_EXEC Params used in pruning expressions have changed, then
-	 * we'd better unset the valid subplans so that they are reselected for
-	 * the new parameter values.
-	 */
-	if (node->as_prune_state &&
-		bms_overlap(node->ps.chgParam,
-					node->as_prune_state->execparamids))
-	{
-		node->as_valid_subplans_identified = false;
-		bms_free(node->as_valid_subplans);
-		node->as_valid_subplans = NULL;
-		bms_free(node->as_valid_asyncplans);
-		node->as_valid_asyncplans = NULL;
-	}
-
-	for (i = 0; i < node->as_nplans; i++)
-	{
-		PlanState  *subnode = node->appendplans[i];
 
-		/*
-		 * ExecReScan doesn't know about my subplans, so I have to do
-		 * changed-parameter signaling myself.
-		 */
-		if (node->ps.chgParam != NULL)
-			UpdateChangedParamSet(subnode, node->ps.chgParam);
+	int			nasyncplans = node->as.nasyncplans;
 
-		/*
-		 * If chgParam of subnode is not null then plan will be re-scanned by
-		 * first ExecProcNode or by first ExecAsyncRequest.
-		 */
-		if (subnode->chgParam == NULL)
-			ExecReScan(subnode);
-	}
+	ExecReScanAppender(&node->as);
 
-	/* Reset async state */
+	/* Reset specific append async state */
 	if (nasyncplans > 0)
 	{
-		i = -1;
-		while ((i = bms_next_member(node->as_asyncplans, i)) >= 0)
-		{
-			AsyncRequest *areq = node->as_asyncrequests[i];
-
-			areq->callback_pending = false;
-			areq->request_complete = false;
-			areq->result = NULL;
-		}
-
 		node->as_nasyncresults = 0;
 		node->as_nasyncremain = 0;
-		bms_free(node->as_needrequest);
-		node->as_needrequest = NULL;
+		bms_free(node->as.needrequest);
 	}
 
 	/* Let choose_next_subplan_* function handle setting the first subplan */
@@ -501,7 +294,7 @@ ExecAppendEstimate(AppendState *node,
 {
 	node->pstate_len =
 		add_size(offsetof(ParallelAppendState, pa_finished),
-				 sizeof(bool) * node->as_nplans);
+				 sizeof(bool) * node->as.nplans);
 
 	shm_toc_estimate_chunk(&pcxt->estimator, node->pstate_len);
 	shm_toc_estimate_keys(&pcxt->estimator, 1);
@@ -523,7 +316,7 @@ ExecAppendInitializeDSM(AppendState *node,
 	pstate = shm_toc_allocate(pcxt->toc, node->pstate_len);
 	memset(pstate, 0, node->pstate_len);
 	LWLockInitialize(&pstate->pa_lock, LWTRANCHE_PARALLEL_APPEND);
-	shm_toc_insert(pcxt->toc, node->ps.plan->plan_node_id, pstate);
+	shm_toc_insert(pcxt->toc, node->as.ps.plan->plan_node_id, pstate);
 
 	node->as_pstate = pstate;
 	node->choose_next_subplan = choose_next_subplan_for_leader;
@@ -541,7 +334,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 	ParallelAppendState *pstate = node->as_pstate;
 
 	pstate->pa_next_plan = 0;
-	memset(pstate->pa_finished, 0, sizeof(bool) * node->as_nplans);
+	memset(pstate->pa_finished, 0, sizeof(bool) * node->as.nplans);
 }
 
 /* ----------------------------------------------------------------
@@ -554,7 +347,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 void
 ExecAppendInitializeWorker(AppendState *node, ParallelWorkerContext *pwcxt)
 {
-	node->as_pstate = shm_toc_lookup(pwcxt->toc, node->ps.plan->plan_node_id, false);
+	node->as_pstate = shm_toc_lookup(pwcxt->toc, node->as.ps.plan->plan_node_id, false);
 	node->choose_next_subplan = choose_next_subplan_for_worker;
 }
 
@@ -572,7 +365,7 @@ choose_next_subplan_locally(AppendState *node)
 	int			nextplan;
 
 	/* We should never be called when there are no subplans */
-	Assert(node->as_nplans > 0);
+	Assert(node->as.nplans > 0);
 
 	/* Nothing to do if syncdone */
 	if (node->as_syncdone)
@@ -587,33 +380,33 @@ choose_next_subplan_locally(AppendState *node)
 	 */
 	if (whichplan == INVALID_SUBPLAN_INDEX)
 	{
-		if (node->as_nasyncplans > 0)
+		if (node->as.nasyncplans > 0)
 		{
 			/* We'd have filled as_valid_subplans already */
-			Assert(node->as_valid_subplans_identified);
+			Assert(node->as.valid_subplans_identified);
 		}
-		else if (!node->as_valid_subplans_identified)
+		else if (!node->as.valid_subplans_identified)
 		{
-			node->as_valid_subplans =
-				ExecFindMatchingSubPlans(node->as_prune_state, false, NULL);
-			node->as_valid_subplans_identified = true;
+			node->as.valid_subplans =
+				ExecFindMatchingSubPlans(node->as.prune_state, false, NULL);
+			node->as.valid_subplans_identified = true;
 		}
 
 		whichplan = -1;
 	}
 
 	/* Ensure whichplan is within the expected range */
-	Assert(whichplan >= -1 && whichplan <= node->as_nplans);
+	Assert(whichplan >= -1 && whichplan <= node->as.nplans);
 
-	if (ScanDirectionIsForward(node->ps.state->es_direction))
-		nextplan = bms_next_member(node->as_valid_subplans, whichplan);
+	if (ScanDirectionIsForward(node->as.ps.state->es_direction))
+		nextplan = bms_next_member(node->as.valid_subplans, whichplan);
 	else
-		nextplan = bms_prev_member(node->as_valid_subplans, whichplan);
+		nextplan = bms_prev_member(node->as.valid_subplans, whichplan);
 
 	if (nextplan < 0)
 	{
 		/* Set as_syncdone if in async mode */
-		if (node->as_nasyncplans > 0)
+		if (node->as.nasyncplans > 0)
 			node->as_syncdone = true;
 		return false;
 	}
@@ -637,10 +430,10 @@ choose_next_subplan_for_leader(AppendState *node)
 	ParallelAppendState *pstate = node->as_pstate;
 
 	/* Backward scan is not supported by parallel-aware plans */
-	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+	Assert(ScanDirectionIsForward(node->as.ps.state->es_direction));
 
 	/* We should never be called when there are no subplans */
-	Assert(node->as_nplans > 0);
+	Assert(node->as.nplans > 0);
 
 	LWLockAcquire(&pstate->pa_lock, LW_EXCLUSIVE);
 
@@ -652,18 +445,18 @@ choose_next_subplan_for_leader(AppendState *node)
 	else
 	{
 		/* Start with last subplan. */
-		node->as_whichplan = node->as_nplans - 1;
+		node->as_whichplan = node->as.nplans - 1;
 
 		/*
 		 * If we've yet to determine the valid subplans then do so now.  If
 		 * run-time pruning is disabled then the valid subplans will always be
 		 * set to all subplans.
 		 */
-		if (!node->as_valid_subplans_identified)
+		if (!node->as.valid_subplans_identified)
 		{
-			node->as_valid_subplans =
-				ExecFindMatchingSubPlans(node->as_prune_state, false, NULL);
-			node->as_valid_subplans_identified = true;
+			node->as.valid_subplans =
+				ExecFindMatchingSubPlans(node->as.prune_state, false, NULL);
+			node->as.valid_subplans_identified = true;
 
 			/*
 			 * Mark each invalid plan as finished to allow the loop below to
@@ -719,10 +512,10 @@ choose_next_subplan_for_worker(AppendState *node)
 	ParallelAppendState *pstate = node->as_pstate;
 
 	/* Backward scan is not supported by parallel-aware plans */
-	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
+	Assert(ScanDirectionIsForward(node->as.ps.state->es_direction));
 
 	/* We should never be called when there are no subplans */
-	Assert(node->as_nplans > 0);
+	Assert(node->as.nplans > 0);
 
 	LWLockAcquire(&pstate->pa_lock, LW_EXCLUSIVE);
 
@@ -735,11 +528,11 @@ choose_next_subplan_for_worker(AppendState *node)
 	 * run-time pruning is disabled then the valid subplans will always be set
 	 * to all subplans.
 	 */
-	else if (!node->as_valid_subplans_identified)
+	else if (!node->as.valid_subplans_identified)
 	{
-		node->as_valid_subplans =
-			ExecFindMatchingSubPlans(node->as_prune_state, false, NULL);
-		node->as_valid_subplans_identified = true;
+		node->as.valid_subplans =
+			ExecFindMatchingSubPlans(node->as.prune_state, false, NULL);
+		node->as.valid_subplans_identified = true;
 
 		mark_invalid_subplans_as_finished(node);
 	}
@@ -759,7 +552,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	{
 		int			nextplan;
 
-		nextplan = bms_next_member(node->as_valid_subplans,
+		nextplan = bms_next_member(node->as.valid_subplans,
 								   pstate->pa_next_plan);
 		if (nextplan >= 0)
 		{
@@ -772,7 +565,7 @@ choose_next_subplan_for_worker(AppendState *node)
 			 * Try looping back to the first valid partial plan, if there is
 			 * one.  If there isn't, arrange to bail out below.
 			 */
-			nextplan = bms_next_member(node->as_valid_subplans,
+			nextplan = bms_next_member(node->as.valid_subplans,
 									   node->as_first_partial_plan - 1);
 			pstate->pa_next_plan =
 				nextplan < 0 ? node->as_whichplan : nextplan;
@@ -797,7 +590,7 @@ choose_next_subplan_for_worker(AppendState *node)
 
 	/* Pick the plan we found, and advance pa_next_plan one more time. */
 	node->as_whichplan = pstate->pa_next_plan;
-	pstate->pa_next_plan = bms_next_member(node->as_valid_subplans,
+	pstate->pa_next_plan = bms_next_member(node->as.valid_subplans,
 										   pstate->pa_next_plan);
 
 	/*
@@ -806,7 +599,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	 */
 	if (pstate->pa_next_plan < 0)
 	{
-		int			nextplan = bms_next_member(node->as_valid_subplans,
+		int			nextplan = bms_next_member(node->as.valid_subplans,
 											   node->as_first_partial_plan - 1);
 
 		if (nextplan >= 0)
@@ -848,16 +641,16 @@ mark_invalid_subplans_as_finished(AppendState *node)
 	Assert(node->as_pstate);
 
 	/* Shouldn't have been called when run-time pruning is not enabled */
-	Assert(node->as_prune_state);
+	Assert(node->as.prune_state);
 
 	/* Nothing to do if all plans are valid */
-	if (bms_num_members(node->as_valid_subplans) == node->as_nplans)
+	if (bms_num_members(node->as.valid_subplans) == node->as.nplans)
 		return;
 
 	/* Mark all non-valid plans as finished */
-	for (i = 0; i < node->as_nplans; i++)
+	for (i = 0; i < node->as.nplans; i++)
 	{
-		if (!bms_is_member(i, node->as_valid_subplans))
+		if (!bms_is_member(i, node->as.valid_subplans))
 			node->as_pstate->pa_finished[i] = true;
 	}
 }
@@ -876,47 +669,25 @@ mark_invalid_subplans_as_finished(AppendState *node)
 static void
 ExecAppendAsyncBegin(AppendState *node)
 {
-	int			i;
-
-	/* Backward scan is not supported by async-aware Appends. */
-	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
-
-	/* We should never be called when there are no subplans */
-	Assert(node->as_nplans > 0);
-
-	/* We should never be called when there are no async subplans. */
-	Assert(node->as_nasyncplans > 0);
-
 	/* If we've yet to determine the valid subplans then do so now. */
-	if (!node->as_valid_subplans_identified)
+	if (!node->as.valid_subplans_identified)
 	{
-		node->as_valid_subplans =
-			ExecFindMatchingSubPlans(node->as_prune_state, false, NULL);
-		node->as_valid_subplans_identified = true;
+		node->as.valid_subplans =
+			ExecFindMatchingSubPlans(node->as.prune_state, false, NULL);
+		node->as.valid_subplans_identified = true;
 
 		classify_matching_subplans(node);
 	}
 
 	/* Initialize state variables. */
-	node->as_syncdone = bms_is_empty(node->as_valid_subplans);
-	node->as_nasyncremain = bms_num_members(node->as_valid_asyncplans);
+	node->as_syncdone = bms_is_empty(node->as.valid_subplans);
+	node->as_nasyncremain = bms_num_members(node->as.valid_asyncplans);
 
 	/* Nothing to do if there are no valid async subplans. */
 	if (node->as_nasyncremain == 0)
 		return;
 
-	/* Make a request for each of the valid async subplans. */
-	i = -1;
-	while ((i = bms_next_member(node->as_valid_asyncplans, i)) >= 0)
-	{
-		AsyncRequest *areq = node->as_asyncrequests[i];
-
-		Assert(areq->request_index == i);
-		Assert(!areq->callback_pending);
-
-		/* Do the actual work. */
-		ExecAsyncRequest(areq);
-	}
+	ExecAppenderAsyncBegin(&node->as);
 }
 
 /* ----------------------------------------------------------------
@@ -961,7 +732,7 @@ ExecAppendAsyncGetNext(AppendState *node, TupleTableSlot **result)
 	if (node->as_syncdone)
 	{
 		Assert(node->as_nasyncremain == 0);
-		*result = ExecClearTuple(node->ps.ps_ResultTupleSlot);
+		*result = ExecClearTuple(node->as.ps.ps_ResultTupleSlot);
 		return true;
 	}
 
@@ -981,7 +752,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 	int			i;
 
 	/* Nothing to do if there are no async subplans needing a new request. */
-	if (bms_is_empty(node->as_needrequest))
+	if (bms_is_empty(node->as.needrequest))
 	{
 		Assert(node->as_nasyncresults == 0);
 		return false;
@@ -994,17 +765,17 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 	if (node->as_nasyncresults > 0)
 	{
 		--node->as_nasyncresults;
-		*result = node->as_asyncresults[node->as_nasyncresults];
+		*result = node->as.asyncresults[node->as_nasyncresults];
 		return true;
 	}
 
 	/* Make a new request for each of the async subplans that need it. */
-	needrequest = node->as_needrequest;
-	node->as_needrequest = NULL;
+	needrequest = node->as.needrequest;
+	node->as.needrequest = NULL;
 	i = -1;
 	while ((i = bms_next_member(needrequest, i)) >= 0)
 	{
-		AsyncRequest *areq = node->as_asyncrequests[i];
+		AsyncRequest *areq = node->as.asyncrequests[i];
 
 		/* Do the actual work. */
 		ExecAsyncRequest(areq);
@@ -1015,7 +786,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 	if (node->as_nasyncresults > 0)
 	{
 		--node->as_nasyncresults;
-		*result = node->as_asyncresults[node->as_nasyncresults];
+		*result = node->as.asyncresults[node->as_nasyncresults];
 		return true;
 	}
 
@@ -1031,105 +802,12 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 static void
 ExecAppendAsyncEventWait(AppendState *node)
 {
-	int			nevents = node->as_nasyncplans + 2;
 	long		timeout = node->as_syncdone ? -1 : 0;
-	WaitEvent	occurred_event[EVENT_BUFFER_SIZE];
-	int			noccurred;
-	int			i;
 
 	/* We should never be called when there are no valid async subplans. */
 	Assert(node->as_nasyncremain > 0);
 
-	Assert(node->as_eventset == NULL);
-	node->as_eventset = CreateWaitEventSet(CurrentResourceOwner, nevents);
-	AddWaitEventToSet(node->as_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
-					  NULL, NULL);
-
-	/* Give each waiting subplan a chance to add an event. */
-	i = -1;
-	while ((i = bms_next_member(node->as_asyncplans, i)) >= 0)
-	{
-		AsyncRequest *areq = node->as_asyncrequests[i];
-
-		if (areq->callback_pending)
-			ExecAsyncConfigureWait(areq);
-	}
-
-	/*
-	 * No need for further processing if none of the subplans configured any
-	 * events.
-	 */
-	if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
-	{
-		FreeWaitEventSet(node->as_eventset);
-		node->as_eventset = NULL;
-		return;
-	}
-
-	/*
-	 * Add the process latch to the set, so that we wake up to process the
-	 * standard interrupts with CHECK_FOR_INTERRUPTS().
-	 *
-	 * NOTE: For historical reasons, it's important that this is added to the
-	 * WaitEventSet after the ExecAsyncConfigureWait() calls.  Namely,
-	 * postgres_fdw calls "GetNumRegisteredWaitEvents(set) == 1" to check if
-	 * any other events are in the set.  That's a poor design, it's
-	 * questionable for postgres_fdw to be doing that in the first place, but
-	 * we cannot change it now.  The pattern has possibly been copied to other
-	 * extensions too.
-	 */
-	AddWaitEventToSet(node->as_eventset, WL_LATCH_SET, PGINVALID_SOCKET,
-					  MyLatch, NULL);
-
-	/* Return at most EVENT_BUFFER_SIZE events in one call. */
-	if (nevents > EVENT_BUFFER_SIZE)
-		nevents = EVENT_BUFFER_SIZE;
-
-	/*
-	 * If the timeout is -1, wait until at least one event occurs.  If the
-	 * timeout is 0, poll for events, but do not wait at all.
-	 */
-	noccurred = WaitEventSetWait(node->as_eventset, timeout, occurred_event,
-								 nevents, WAIT_EVENT_APPEND_READY);
-	FreeWaitEventSet(node->as_eventset);
-	node->as_eventset = NULL;
-	if (noccurred == 0)
-		return;
-
-	/* Deliver notifications. */
-	for (i = 0; i < noccurred; i++)
-	{
-		WaitEvent  *w = &occurred_event[i];
-
-		/*
-		 * Each waiting subplan should have registered its wait event with
-		 * user_data pointing back to its AsyncRequest.
-		 */
-		if ((w->events & WL_SOCKET_READABLE) != 0)
-		{
-			AsyncRequest *areq = (AsyncRequest *) w->user_data;
-
-			if (areq->callback_pending)
-			{
-				/*
-				 * Mark it as no longer needing a callback.  We must do this
-				 * before dispatching the callback in case the callback resets
-				 * the flag.
-				 */
-				areq->callback_pending = false;
-
-				/* Do the actual work. */
-				ExecAsyncNotify(areq);
-			}
-		}
-
-		/* Handle standard interrupts */
-		if ((w->events & WL_LATCH_SET) != 0)
-		{
-			ResetLatch(MyLatch);
-			CHECK_FOR_INTERRUPTS();
-		}
-	}
+	ExecAppenderAsyncEventWait(&node->as, timeout, WAIT_EVENT_APPEND_READY);
 }
 
 /* ----------------------------------------------------------------
@@ -1165,14 +843,14 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 	}
 
 	/* Save result so we can return it. */
-	Assert(node->as_nasyncresults < node->as_nasyncplans);
-	node->as_asyncresults[node->as_nasyncresults++] = slot;
+	Assert(node->as_nasyncresults < node->as.nasyncplans);
+	node->as.asyncresults[node->as_nasyncresults++] = slot;
 
 	/*
 	 * Mark the subplan that returned a result as ready for a new request.  We
 	 * don't launch another one here immediately because it might complete.
 	 */
-	node->as_needrequest = bms_add_member(node->as_needrequest,
+	node->as.needrequest = bms_add_member(node->as.needrequest,
 										  areq->request_index);
 }
 
@@ -1187,10 +865,10 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 static void
 classify_matching_subplans(AppendState *node)
 {
-	Assert(node->as_valid_subplans_identified);
+	Assert(node->as.valid_subplans_identified);
 
 	/* Nothing to do if there are no valid subplans. */
-	if (bms_is_empty(node->as_valid_subplans))
+	if (bms_is_empty(node->as.valid_subplans))
 	{
 		node->as_syncdone = true;
 		node->as_nasyncremain = 0;
@@ -1199,8 +877,8 @@ classify_matching_subplans(AppendState *node)
 
 	/* No valid async subplans identified. */
 	if (!classify_matching_subplans_common(
-										   &node->as_valid_subplans,
-										   node->as_asyncplans,
-										   &node->as_valid_asyncplans))
+										   &node->as.valid_subplans,
+										   node->as.asyncplans,
+										   &node->as.valid_asyncplans))
 		node->as_nasyncremain = 0;
 }
diff --git a/src/backend/executor/nodeMergeAppend.c b/src/backend/executor/nodeMergeAppend.c
index f1c267eb9eb..6eb8c80bc4c 100644
--- a/src/backend/executor/nodeMergeAppend.c
+++ b/src/backend/executor/nodeMergeAppend.c
@@ -38,6 +38,7 @@
 
 #include "postgres.h"
 
+#include "executor/execAppend.h"
 #include "executor/executor.h"
 #include "executor/execAsync.h"
 #include "executor/execPartition.h"
@@ -76,14 +77,7 @@ MergeAppendState *
 ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 {
 	MergeAppendState *mergestate = makeNode(MergeAppendState);
-	PlanState **mergeplanstates;
-	const TupleTableSlotOps *mergeops;
-	Bitmapset  *validsubplans;
-	int			nplans;
-	int			i,
-				j;
-	Bitmapset  *asyncplans;
-	int			nasyncplans;
+	int			i;
 
 	/* check for unsupported flags */
 	Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
@@ -91,154 +85,27 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	/*
 	 * create new MergeAppendState for our node
 	 */
-	mergestate->ps.plan = (Plan *) node;
-	mergestate->ps.state = estate;
-	mergestate->ps.ExecProcNode = ExecMergeAppend;
-
-	/* If run-time partition pruning is enabled, then set that up now */
-	if (node->part_prune_index >= 0)
-	{
-		PartitionPruneState *prunestate;
-
-		/*
-		 * Set up pruning data structure.  This also initializes the set of
-		 * subplans to initialize (validsubplans) by taking into account the
-		 * result of performing initial pruning if any.
-		 */
-		prunestate = ExecInitPartitionExecPruning(&mergestate->ps,
-												  list_length(node->mergeplans),
-												  node->part_prune_index,
-												  node->apprelids,
-												  &validsubplans);
-		mergestate->ms_prune_state = prunestate;
-		nplans = bms_num_members(validsubplans);
-
-		/*
-		 * When no run-time pruning is required and there's at least one
-		 * subplan, we can fill ms_valid_subplans immediately, preventing
-		 * later calls to ExecFindMatchingSubPlans.
-		 */
-		if (!prunestate->do_exec_prune && nplans > 0)
-		{
-			mergestate->ms_valid_subplans = bms_add_range(NULL, 0, nplans - 1);
-			mergestate->ms_valid_subplans_identified = true;
-		}
-	}
-	else
-	{
-		nplans = list_length(node->mergeplans);
-
-		/*
-		 * When run-time partition pruning is not enabled we can just mark all
-		 * subplans as valid; they must also all be initialized.
-		 */
-		Assert(nplans > 0);
-		mergestate->ms_valid_subplans = validsubplans =
-			bms_add_range(NULL, 0, nplans - 1);
-		mergestate->ms_valid_subplans_identified = true;
-		mergestate->ms_prune_state = NULL;
-	}
-
-	mergeplanstates = palloc_array(PlanState *, nplans);
-	mergestate->mergeplans = mergeplanstates;
-	mergestate->ms_nplans = nplans;
-
-	mergestate->ms_slots = palloc0_array(TupleTableSlot *, nplans);
-	mergestate->ms_heap = binaryheap_allocate(nplans, heap_compare_slots,
+	mergestate->ms.ps.plan = (Plan *) node;
+	mergestate->ms.ps.state = estate;
+	mergestate->ms.ps.ExecProcNode = ExecMergeAppend;
+
+	/* Initialize common fields */
+	ExecInitAppender(&mergestate->ms,
+			&node->ap,
+			estate,
+			eflags,
+			-1,
+			NULL);
+
+	if (mergestate->ms.nasyncplans > 0 && mergestate->ms.valid_subplans_identified)
+		classify_matching_subplans(mergestate);
+
+	mergestate->ms_slots = palloc0_array(TupleTableSlot *, mergestate->ms.nplans);
+	mergestate->ms_heap = binaryheap_allocate(mergestate->ms.nplans, heap_compare_slots,
 											  mergestate);
 
-	/*
-	 * call ExecInitNode on each of the valid plans to be executed and save
-	 * the results into the mergeplanstates array.
-	 */
-	j = 0;
-	asyncplans = NULL;
-	nasyncplans = 0;
-
-	i = -1;
-	while ((i = bms_next_member(validsubplans, i)) >= 0)
-	{
-		Plan	   *initNode = (Plan *) list_nth(node->mergeplans, i);
-
-		/*
-		 * Record async subplans.  When executing EvalPlanQual, we treat them
-		 * as sync ones; don't do this when initializing an EvalPlanQual plan
-		 * tree.
-		 */
-		if (initNode->async_capable && estate->es_epq_active == NULL)
-		{
-			asyncplans = bms_add_member(asyncplans, j);
-			nasyncplans++;
-		}
-
-		mergeplanstates[j++] = ExecInitNode(initNode, estate, eflags);
-	}
-
-	/*
-	 * Initialize MergeAppend's result tuple type and slot.  If the child
-	 * plans all produce the same fixed slot type, we can use that slot type;
-	 * otherwise make a virtual slot.  (Note that the result slot itself is
-	 * used only to return a null tuple at end of execution; real tuples are
-	 * returned to the caller in the children's own result slots.  What we are
-	 * doing here is allowing the parent plan node to optimize if the
-	 * MergeAppend will return only one kind of slot.)
-	 */
-	mergeops = ExecGetCommonSlotOps(mergeplanstates, j);
-	if (mergeops != NULL)
-	{
-		ExecInitResultTupleSlotTL(&mergestate->ps, mergeops);
-	}
-	else
-	{
-		ExecInitResultTupleSlotTL(&mergestate->ps, &TTSOpsVirtual);
-		/* show that the output slot type is not fixed */
-		mergestate->ps.resultopsset = true;
-		mergestate->ps.resultopsfixed = false;
-	}
-
-	/*
-	 * Miscellaneous initialization
-	 */
-	mergestate->ps.ps_ProjInfo = NULL;
-
-	/* Initialize async state */
-	mergestate->ms_asyncplans = asyncplans;
-	mergestate->ms_nasyncplans = nasyncplans;
-	mergestate->ms_asyncrequests = NULL;
-	mergestate->ms_asyncresults = NULL;
 	mergestate->ms_has_asyncresults = NULL;
 	mergestate->ms_asyncremain = NULL;
-	mergestate->ms_needrequest = NULL;
-	mergestate->ms_eventset = NULL;
-	mergestate->ms_valid_asyncplans = NULL;
-
-	if (nasyncplans > 0)
-	{
-		mergestate->ms_asyncrequests = (AsyncRequest **)
-			palloc0(nplans * sizeof(AsyncRequest *));
-
-		i = -1;
-		while ((i = bms_next_member(asyncplans, i)) >= 0)
-		{
-			AsyncRequest *areq;
-
-			areq = palloc(sizeof(AsyncRequest));
-			areq->requestor = (PlanState *) mergestate;
-			areq->requestee = mergeplanstates[i];
-			areq->request_index = i;
-			areq->callback_pending = false;
-			areq->request_complete = false;
-			areq->result = NULL;
-
-			mergestate->ms_asyncrequests[i] = areq;
-		}
-
-		mergestate->ms_asyncresults = (TupleTableSlot **)
-			palloc0(nplans * sizeof(TupleTableSlot *));
-
-		if (mergestate->ms_valid_subplans_identified)
-			classify_matching_subplans(mergestate);
-	}
 
 	/*
 	 * initialize sort-key information
@@ -293,20 +160,20 @@ ExecMergeAppend(PlanState *pstate)
 	if (!node->ms_initialized)
 	{
 		/* Nothing to do if all subplans were pruned */
-		if (node->ms_nplans == 0)
-			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+		if (node->ms.nplans == 0)
+			return ExecClearTuple(node->ms.ps.ps_ResultTupleSlot);
 
 		/* If we've yet to determine the valid subplans then do so now. */
-		if (!node->ms_valid_subplans_identified)
+		if (!node->ms.valid_subplans_identified)
 		{
-			node->ms_valid_subplans =
-				ExecFindMatchingSubPlans(node->ms_prune_state, false, NULL);
-			node->ms_valid_subplans_identified = true;
+			node->ms.valid_subplans =
+				ExecFindMatchingSubPlans(node->ms.prune_state, false, NULL);
+			node->ms.valid_subplans_identified = true;
 			classify_matching_subplans(node);
 		}
 
 		/* If there are any async subplans, begin executing them. */
-		if (node->ms_nasyncplans > 0)
+		if (node->ms.nasyncplans > 0)
 			ExecMergeAppendAsyncBegin(node);
 
 		/*
@@ -314,16 +181,16 @@ ExecMergeAppend(PlanState *pstate)
 		 * and set up the heap.
 		 */
 		i = -1;
-		while ((i = bms_next_member(node->ms_valid_subplans, i)) >= 0)
+		while ((i = bms_next_member(node->ms.valid_subplans, i)) >= 0)
 		{
-			node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
+			node->ms_slots[i] = ExecProcNode(node->ms.plans[i]);
 			if (!TupIsNull(node->ms_slots[i]))
 				binaryheap_add_unordered(node->ms_heap, Int32GetDatum(i));
 		}
 
 		/* Look at valid async subplans */
 		i = -1;
-		while ((i = bms_next_member(node->ms_valid_asyncplans, i)) >= 0)
+		while ((i = bms_next_member(node->ms.valid_asyncplans, i)) >= 0)
 		{
 			ExecMergeAppendAsyncGetNext(node, i);
 			if (!TupIsNull(node->ms_slots[i]))
@@ -344,12 +211,12 @@ ExecMergeAppend(PlanState *pstate)
 		 * to not pull tuples until necessary.)
 		 */
 		i = DatumGetInt32(binaryheap_first(node->ms_heap));
-		if (bms_is_member(i, node->ms_asyncplans))
+		if (bms_is_member(i, node->ms.asyncplans))
 			ExecMergeAppendAsyncGetNext(node, i);
 		else
 		{
-			Assert(bms_is_member(i, node->ms_valid_subplans));
-			node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
+			Assert(bms_is_member(i, node->ms.valid_subplans));
+			node->ms_slots[i] = ExecProcNode(node->ms.plans[i]);
 		}
 		if (!TupIsNull(node->ms_slots[i]))
 			binaryheap_replace_first(node->ms_heap, Int32GetDatum(i));
@@ -360,7 +227,7 @@ ExecMergeAppend(PlanState *pstate)
 	if (binaryheap_empty(node->ms_heap))
 	{
 		/* All the subplans are exhausted, and so is the heap */
-		result = ExecClearTuple(node->ps.ps_ResultTupleSlot);
+		result = ExecClearTuple(node->ms.ps.ps_ResultTupleSlot);
 	}
 	else
 	{
@@ -426,81 +293,22 @@ heap_compare_slots(Datum a, Datum b, void *arg)
 void
 ExecEndMergeAppend(MergeAppendState *node)
 {
-	PlanState **mergeplans;
-	int			nplans;
-	int			i;
-
-	/*
-	 * get information from the node
-	 */
-	mergeplans = node->mergeplans;
-	nplans = node->ms_nplans;
-
-	/*
-	 * shut down each of the subscans
-	 */
-	for (i = 0; i < nplans; i++)
-		ExecEndNode(mergeplans[i]);
+	ExecEndAppender(&node->ms);
 }
 
 void
 ExecReScanMergeAppend(MergeAppendState *node)
 {
-	int			i;
-	int			nasyncplans = node->ms_nasyncplans;
+	int			nasyncplans = node->ms.nasyncplans;
 
-	/*
-	 * If any PARAM_EXEC Params used in pruning expressions have changed, then
-	 * we'd better unset the valid subplans so that they are reselected for
-	 * the new parameter values.
-	 */
-	if (node->ms_prune_state &&
-		bms_overlap(node->ps.chgParam,
-					node->ms_prune_state->execparamids))
-	{
-		node->ms_valid_subplans_identified = false;
-		bms_free(node->ms_valid_subplans);
-		node->ms_valid_subplans = NULL;
-		bms_free(node->ms_valid_asyncplans);
-		node->ms_valid_asyncplans = NULL;
-	}
-
-	for (i = 0; i < node->ms_nplans; i++)
-	{
-		PlanState  *subnode = node->mergeplans[i];
-
-		/*
-		 * ExecReScan doesn't know about my subplans, so I have to do
-		 * changed-parameter signaling myself.
-		 */
-		if (node->ps.chgParam != NULL)
-			UpdateChangedParamSet(subnode, node->ps.chgParam);
-
-		/*
-		 * If chgParam of subnode is not null then plan will be re-scanned by
-		 * first ExecProcNode.
-		 */
-		if (subnode->chgParam == NULL)
-			ExecReScan(subnode);
-	}
+	ExecReScanAppender(&node->ms);
 
-	/* Reset async state */
+	/* Reset specific merge append async state */
 	if (nasyncplans > 0)
 	{
-		i = -1;
-		while ((i = bms_next_member(node->ms_asyncplans, i)) >= 0)
-		{
-			AsyncRequest *areq = node->ms_asyncrequests[i];
-
-			areq->callback_pending = false;
-			areq->request_complete = false;
-			areq->result = NULL;
-		}
-
 		bms_free(node->ms_asyncremain);
 		node->ms_asyncremain = NULL;
-		bms_free(node->ms_needrequest);
-		node->ms_needrequest = NULL;
+		bms_free(node->ms.needrequest);
 		bms_free(node->ms_has_asyncresults);
 		node->ms_has_asyncresults = NULL;
 	}
@@ -519,10 +327,10 @@ ExecReScanMergeAppend(MergeAppendState *node)
 static void
 classify_matching_subplans(MergeAppendState *node)
 {
-	Assert(node->ms_valid_subplans_identified);
+	Assert(node->ms.valid_subplans_identified);
 
 	/* Nothing to do if there are no valid subplans. */
-	if (bms_is_empty(node->ms_valid_subplans))
+	if (bms_is_empty(node->ms.valid_subplans))
 	{
 		node->ms_asyncremain = NULL;
 		return;
@@ -530,9 +338,9 @@ classify_matching_subplans(MergeAppendState *node)
 
 	/* No valid async subplans identified. */
 	if (!classify_matching_subplans_common(
-										   &node->ms_valid_subplans,
-										   node->ms_asyncplans,
-										   &node->ms_valid_asyncplans))
+										   &node->ms.valid_subplans,
+										   node->ms.asyncplans,
+										   &node->ms.valid_asyncplans))
 		node->ms_asyncremain = NULL;
 }
 
@@ -545,39 +353,17 @@ classify_matching_subplans(MergeAppendState *node)
 static void
 ExecMergeAppendAsyncBegin(MergeAppendState *node)
 {
-	int			i;
-
-	/* Backward scan is not supported by async-aware MergeAppends. */
-	Assert(ScanDirectionIsForward(node->ps.state->es_direction));
-
-	/* We should never be called when there are no subplans */
-	Assert(node->ms_nplans > 0);
-
-	/* We should never be called when there are no async subplans. */
-	Assert(node->ms_nasyncplans > 0);
-
 	/* ExecMergeAppend() identifies valid subplans */
-	Assert(node->ms_valid_subplans_identified);
+	Assert(node->ms.valid_subplans_identified);
 
 	/* Initialize state variables. */
-	node->ms_asyncremain = bms_copy(node->ms_valid_asyncplans);
+	node->ms_asyncremain = bms_copy(node->ms.valid_asyncplans);
 
 	/* Nothing to do if there are no valid async subplans. */
 	if (bms_is_empty(node->ms_asyncremain))
 		return;
 
-	/* Make a request for each of the valid async subplans. */
-	i = -1;
-	while ((i = bms_next_member(node->ms_valid_asyncplans, i)) >= 0)
-	{
-		AsyncRequest *areq = node->ms_asyncrequests[i];
-
-		Assert(areq->request_index == i);
-		Assert(!areq->callback_pending);
-
-		/* Do the actual work. */
-		ExecAsyncRequest(areq);
-	}
+	ExecAppenderAsyncBegin(&node->ms);
 }
 
 /* ----------------------------------------------------------------
@@ -638,7 +424,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 	 */
 	if (bms_is_member(mplan, node->ms_has_asyncresults))
 	{
-		node->ms_slots[mplan] = node->ms_asyncresults[mplan];
+		node->ms_slots[mplan] = node->ms.asyncresults[mplan];
 		return true;
 	}
 
@@ -648,7 +434,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 	 */
 	needrequest = NULL;
 	i = -1;
-	while ((i = bms_next_member(node->ms_needrequest, i)) >= 0)
+	while ((i = bms_next_member(node->ms.needrequest, i)) >= 0)
 	{
 		if (!bms_is_member(i, node->ms_has_asyncresults))
 			needrequest = bms_add_member(needrequest, i);
@@ -661,13 +447,13 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 		return false;
 
 	/* Clear ms_needrequest flag, as we are going to send requests now */
-	node->ms_needrequest = bms_del_members(node->ms_needrequest, needrequest);
+	node->ms.needrequest = bms_del_members(node->ms.needrequest, needrequest);
 
 	/* Make a new request for each of the async subplans that need it. */
 	i = -1;
 	while ((i = bms_next_member(needrequest, i)) >= 0)
 	{
-		AsyncRequest *areq = node->ms_asyncrequests[i];
+		AsyncRequest *areq = node->ms.asyncrequests[i];
 
 		/*
 		 * We've just checked that subplan doesn't already have some fetched
@@ -683,7 +469,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 	/* Return needed asynchronously-generated results if any. */
 	if (bms_is_member(mplan, node->ms_has_asyncresults))
 	{
-		node->ms_slots[mplan] = node->ms_asyncresults[mplan];
+		node->ms_slots[mplan] = node->ms.asyncresults[mplan];
 		return true;
 	}
 
@@ -707,7 +493,7 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 	/* We should handle previous async result prior to getting new one */
 	Assert(!bms_is_member(areq->request_index, node->ms_has_asyncresults));
 
-	node->ms_asyncresults[areq->request_index] = NULL;
+	node->ms.asyncresults[areq->request_index] = NULL;
 	/* Nothing to do if the request is pending. */
 	if (!areq->request_complete)
 	{
@@ -730,13 +516,13 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 	node->ms_has_asyncresults = bms_add_member(node->ms_has_asyncresults,
 											   areq->request_index);
 	/* Save result so we can return it. */
-	node->ms_asyncresults[areq->request_index] = slot;
+	node->ms.asyncresults[areq->request_index] = slot;
 
 	/*
 	 * Mark the subplan that returned a result as ready for a new request.  We
 	 * don't launch another one here immediately because it might complete.
 	 */
-	node->ms_needrequest = bms_add_member(node->ms_needrequest,
+	node->ms.needrequest = bms_add_member(node->ms.needrequest,
 										  areq->request_index);
 }
 
@@ -749,101 +535,8 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 static void
 ExecMergeAppendAsyncEventWait(MergeAppendState *node)
 {
-	int			nevents = node->ms_nasyncplans + 2; /* one for PM death and
-													 * one for latch */
-	WaitEvent	occurred_event[EVENT_BUFFER_SIZE];
-	int			noccurred;
-	int			i;
-
 	/* We should never be called when there are no valid async subplans. */
 	Assert(bms_num_members(node->ms_asyncremain) > 0);
 
-	node->ms_eventset = CreateWaitEventSet(CurrentResourceOwner, nevents);
-	AddWaitEventToSet(node->ms_eventset, WL_EXIT_ON_PM_DEATH, PGINVALID_SOCKET,
-					  NULL, NULL);
-
-	/* Give each waiting subplan a chance to add an event. */
-	i = -1;
-	while ((i = bms_next_member(node->ms_asyncplans, i)) >= 0)
-	{
-		AsyncRequest *areq = node->ms_asyncrequests[i];
-
-		if (areq->callback_pending)
-			ExecAsyncConfigureWait(areq);
-	}
-
-	/*
-	 * No need for further processing if none of the subplans configured any
-	 * events.
-	 */
-	if (GetNumRegisteredWaitEvents(node->ms_eventset) == 1)
-	{
-		FreeWaitEventSet(node->ms_eventset);
-		node->ms_eventset = NULL;
-		return;
-	}
-
-	/*
-	 * Add the process latch to the set, so that we wake up to process the
-	 * standard interrupts with CHECK_FOR_INTERRUPTS().
-	 *
-	 * NOTE: For historical reasons, it's important that this is added to the
-	 * WaitEventSet after the ExecAsyncConfigureWait() calls.  Namely,
-	 * postgres_fdw calls "GetNumRegisteredWaitEvents(set) == 1" to check if
-	 * any other events are in the set.  That's a poor design, it's
-	 * questionable for postgres_fdw to be doing that in the first place, but
-	 * we cannot change it now.  The pattern has possibly been copied to other
-	 * extensions too.
-	 */
-	AddWaitEventToSet(node->ms_eventset, WL_LATCH_SET, PGINVALID_SOCKET,
-					  MyLatch, NULL);
-
-	/* Return at most EVENT_BUFFER_SIZE events in one call. */
-	if (nevents > EVENT_BUFFER_SIZE)
-		nevents = EVENT_BUFFER_SIZE;
-
-	/*
-	 * Wait until at least one event occurs.
-	 */
-	noccurred = WaitEventSetWait(node->ms_eventset, -1 /* no timeout */ , occurred_event,
-								 nevents, WAIT_EVENT_APPEND_READY);
-	FreeWaitEventSet(node->ms_eventset);
-	node->ms_eventset = NULL;
-	if (noccurred == 0)
-		return;
-
-	/* Deliver notifications. */
-	for (i = 0; i < noccurred; i++)
-	{
-		WaitEvent  *w = &occurred_event[i];
-
-		/*
-		 * Each waiting subplan should have registered its wait event with
-		 * user_data pointing back to its AsyncRequest.
-		 */
-		if ((w->events & WL_SOCKET_READABLE) != 0)
-		{
-			AsyncRequest *areq = (AsyncRequest *) w->user_data;
-
-			if (areq->callback_pending)
-			{
-				/*
-				 * Mark it as no longer needing a callback.  We must do this
-				 * before dispatching the callback in case the callback resets
-				 * the flag.
-				 */
-				areq->callback_pending = false;
-
-				/* Do the actual work. */
-				ExecAsyncNotify(areq);
-			}
-		}
-
-		/* Handle standard interrupts */
-		if ((w->events & WL_LATCH_SET) != 0)
-		{
-			ResetLatch(MyLatch);
-			CHECK_FOR_INTERRUPTS();
-		}
-	}
+	ExecAppenderAsyncEventWait(&node->ms, -1 /* no timeout */, WAIT_EVENT_APPEND_READY);
 }
diff --git a/src/backend/nodes/nodeFuncs.c b/src/backend/nodes/nodeFuncs.c
index 024a2b2fd84..2f4e2ae6d39 100644
--- a/src/backend/nodes/nodeFuncs.c
+++ b/src/backend/nodes/nodeFuncs.c
@@ -4751,14 +4751,14 @@ planstate_tree_walker_impl(PlanState *planstate,
 	switch (nodeTag(plan))
 	{
 		case T_Append:
-			if (planstate_walk_members(((AppendState *) planstate)->appendplans,
-									   ((AppendState *) planstate)->as_nplans,
+			if (planstate_walk_members(((AppendState *) planstate)->as.plans,
+									   ((AppendState *) planstate)->as.nplans,
 									   walker, context))
 				return true;
 			break;
 		case T_MergeAppend:
-			if (planstate_walk_members(((MergeAppendState *) planstate)->mergeplans,
-									   ((MergeAppendState *) planstate)->ms_nplans,
+			if (planstate_walk_members(((MergeAppendState *) planstate)->ms.plans,
+									   ((MergeAppendState *) planstate)->ms.nplans,
 									   walker, context))
 				return true;
 			break;
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 24325d42f0d..bb84040e8f9 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1262,11 +1262,11 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 	 * child plans, to make cross-checking the sort info easier.
 	 */
 	plan = makeNode(Append);
-	plan->plan.targetlist = tlist;
-	plan->plan.qual = NIL;
-	plan->plan.lefttree = NULL;
-	plan->plan.righttree = NULL;
-	plan->apprelids = rel->relids;
+	plan->ap.plan.targetlist = tlist;
+	plan->ap.plan.qual = NIL;
+	plan->ap.plan.lefttree = NULL;
+	plan->ap.plan.righttree = NULL;
+	plan->ap.apprelids = rel->relids;
 
 	if (pathkeys != NIL)
 	{
@@ -1285,7 +1285,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 										  &nodeSortOperators,
 										  &nodeCollations,
 										  &nodeNullsFirst);
-		tlist_was_changed = (orig_tlist_length != list_length(plan->plan.targetlist));
+		tlist_was_changed = (orig_tlist_length != list_length(plan->ap.plan.targetlist));
 	}
 
 	/* If appropriate, consider async append */
@@ -1395,7 +1395,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 	}
 
 	/* Set below if we find quals that we can use to run-time prune */
-	plan->part_prune_index = -1;
+	plan->ap.part_prune_index = -1;
 
 	/*
 	 * If any quals exist, they may be useful to perform further partition
@@ -1420,16 +1420,16 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 		}
 
 		if (prunequal != NIL)
-			plan->part_prune_index = make_partition_pruneinfo(root, rel,
+			plan->ap.part_prune_index = make_partition_pruneinfo(root, rel,
 															  best_path->subpaths,
 															  prunequal);
 	}
 
-	plan->appendplans = subplans;
+	plan->ap.subplans = subplans;
 	plan->nasyncplans = nasyncplans;
 	plan->first_partial_plan = best_path->first_partial_path;
 
-	copy_generic_path_info(&plan->plan, (Path *) best_path);
+	copy_generic_path_info(&plan->ap.plan, (Path *) best_path);
 
 	/*
 	 * If prepare_sort_from_pathkeys added sort columns, but we were told to
@@ -1438,9 +1438,9 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 	 */
 	if (tlist_was_changed && (flags & (CP_EXACT_TLIST | CP_SMALL_TLIST)))
 	{
-		tlist = list_copy_head(plan->plan.targetlist, orig_tlist_length);
+		tlist = list_copy_head(plan->ap.plan.targetlist, orig_tlist_length);
 		return inject_projection_plan((Plan *) plan, tlist,
-									  plan->plan.parallel_safe);
+									  plan->ap.plan.parallel_safe);
 	}
 	else
 		return (Plan *) plan;
@@ -1458,7 +1458,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 						 int flags)
 {
 	MergeAppend *node = makeNode(MergeAppend);
-	Plan	   *plan = &node->plan;
+	Plan	   *plan = &node->ap.plan;
 	List	   *tlist = build_path_tlist(root, &best_path->path);
 	int			orig_tlist_length = list_length(tlist);
 	bool		tlist_was_changed;
@@ -1479,7 +1479,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->qual = NIL;
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
-	node->apprelids = rel->relids;
+	node->ap.apprelids = rel->relids;
 
 	consider_async = (enable_async_merge_append &&
 					  !best_path->path.parallel_safe &&
@@ -1593,7 +1593,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	}
 
 	/* Set below if we find quals that we can use to run-time prune */
-	node->part_prune_index = -1;
+	node->ap.part_prune_index = -1;
 
 	/*
 	 * If any quals exist, they may be useful to perform further partition
@@ -1610,12 +1610,12 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 		Assert(best_path->path.param_info == NULL);
 
 		if (prunequal != NIL)
-			node->part_prune_index = make_partition_pruneinfo(root, rel,
+			node->ap.part_prune_index = make_partition_pruneinfo(root, rel,
 															  best_path->subpaths,
 															  prunequal);
 	}
 
-	node->mergeplans = subplans;
+	node->ap.subplans = subplans;
 
 	/*
 	 * If prepare_sort_from_pathkeys added sort columns, but we were told to
diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index cd7ea1e6b58..a595f34c87b 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1850,10 +1850,10 @@ set_append_references(PlannerInfo *root,
 	 * check quals.  If it's got exactly one child plan, then it's not doing
 	 * anything useful at all, and we can strip it out.
 	 */
-	Assert(aplan->plan.qual == NIL);
+	Assert(aplan->ap.plan.qual == NIL);
 
 	/* First, we gotta recurse on the children */
-	foreach(l, aplan->appendplans)
+	foreach(l, aplan->ap.subplans)
 	{
 		lfirst(l) = set_plan_refs(root, (Plan *) lfirst(l), rtoffset);
 	}
@@ -1866,11 +1866,11 @@ set_append_references(PlannerInfo *root,
 	 * plan may execute the non-parallel aware child multiple times.  (If you
 	 * change these rules, update create_append_path to match.)
 	 */
-	if (list_length(aplan->appendplans) == 1)
+	if (list_length(aplan->ap.subplans) == 1)
 	{
-		Plan	   *p = (Plan *) linitial(aplan->appendplans);
+		Plan	   *p = (Plan *) linitial(aplan->ap.subplans);
 
-		if (p->parallel_aware == aplan->plan.parallel_aware)
+		if (p->parallel_aware == aplan->ap.plan.parallel_aware)
 			return clean_up_removed_plan_level((Plan *) aplan, p);
 	}
 
@@ -1881,19 +1881,19 @@ set_append_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) aplan, rtoffset);
 
-	aplan->apprelids = offset_relid_set(aplan->apprelids, rtoffset);
+	aplan->ap.apprelids = offset_relid_set(aplan->ap.apprelids, rtoffset);
 
 	/*
 	 * Add PartitionPruneInfo, if any, to PlannerGlobal and update the index.
 	 * Also update the RT indexes present in it to add the offset.
 	 */
-	if (aplan->part_prune_index >= 0)
-		aplan->part_prune_index =
-			register_partpruneinfo(root, aplan->part_prune_index, rtoffset);
+	if (aplan->ap.part_prune_index >= 0)
+		aplan->ap.part_prune_index =
+			register_partpruneinfo(root, aplan->ap.part_prune_index, rtoffset);
 
 	/* We don't need to recurse to lefttree or righttree ... */
-	Assert(aplan->plan.lefttree == NULL);
-	Assert(aplan->plan.righttree == NULL);
+	Assert(aplan->ap.plan.lefttree == NULL);
+	Assert(aplan->ap.plan.righttree == NULL);
 
 	return (Plan *) aplan;
 }
@@ -1917,10 +1917,10 @@ set_mergeappend_references(PlannerInfo *root,
 	 * or check quals.  If it's got exactly one child plan, then it's not
 	 * doing anything useful at all, and we can strip it out.
 	 */
-	Assert(mplan->plan.qual == NIL);
+	Assert(mplan->ap.plan.qual == NIL);
 
 	/* First, we gotta recurse on the children */
-	foreach(l, mplan->mergeplans)
+	foreach(l, mplan->ap.subplans)
 	{
 		lfirst(l) = set_plan_refs(root, (Plan *) lfirst(l), rtoffset);
 	}
@@ -1934,11 +1934,11 @@ set_mergeappend_references(PlannerInfo *root,
 	 * multiple times.  (If you change these rules, update
 	 * create_merge_append_path to match.)
 	 */
-	if (list_length(mplan->mergeplans) == 1)
+	if (list_length(mplan->ap.subplans) == 1)
 	{
-		Plan	   *p = (Plan *) linitial(mplan->mergeplans);
+		Plan	   *p = (Plan *) linitial(mplan->ap.subplans);
 
-		if (p->parallel_aware == mplan->plan.parallel_aware)
+		if (p->parallel_aware == mplan->ap.plan.parallel_aware)
 			return clean_up_removed_plan_level((Plan *) mplan, p);
 	}
 
@@ -1949,19 +1949,19 @@ set_mergeappend_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) mplan, rtoffset);
 
-	mplan->apprelids = offset_relid_set(mplan->apprelids, rtoffset);
+	mplan->ap.apprelids = offset_relid_set(mplan->ap.apprelids, rtoffset);
 
 	/*
 	 * Add PartitionPruneInfo, if any, to PlannerGlobal and update the index.
 	 * Also update the RT indexes present in it to add the offset.
 	 */
-	if (mplan->part_prune_index >= 0)
-		mplan->part_prune_index =
-			register_partpruneinfo(root, mplan->part_prune_index, rtoffset);
+	if (mplan->ap.part_prune_index >= 0)
+		mplan->ap.part_prune_index =
+			register_partpruneinfo(root, mplan->ap.part_prune_index, rtoffset);
 
 	/* We don't need to recurse to lefttree or righttree ... */
-	Assert(mplan->plan.lefttree == NULL);
-	Assert(mplan->plan.righttree == NULL);
+	Assert(mplan->ap.plan.lefttree == NULL);
+	Assert(mplan->ap.plan.righttree == NULL);
 
 	return (Plan *) mplan;
 }
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index ff63d20f8d5..eb616c977bc 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -2759,7 +2759,7 @@ finalize_plan(PlannerInfo *root, Plan *plan,
 
 		case T_Append:
 			{
-				foreach(l, ((Append *) plan)->appendplans)
+				foreach(l, ((Append *) plan)->ap.subplans)
 				{
 					context.paramids =
 						bms_add_members(context.paramids,
@@ -2774,7 +2774,7 @@ finalize_plan(PlannerInfo *root, Plan *plan,
 
 		case T_MergeAppend:
 			{
-				foreach(l, ((MergeAppend *) plan)->mergeplans)
+				foreach(l, ((MergeAppend *) plan)->ap.subplans)
 				{
 					context.paramids =
 						bms_add_members(context.paramids,
diff --git a/src/backend/utils/adt/ruleutils.c b/src/backend/utils/adt/ruleutils.c
index 9f85eb86da1..ce57f80e5e3 100644
--- a/src/backend/utils/adt/ruleutils.c
+++ b/src/backend/utils/adt/ruleutils.c
@@ -5163,9 +5163,9 @@ set_deparse_plan(deparse_namespace *dpns, Plan *plan)
 	 * natural choice.
 	 */
 	if (IsA(plan, Append))
-		dpns->outer_plan = linitial(((Append *) plan)->appendplans);
+		dpns->outer_plan = linitial(((Append *) plan)->ap.subplans);
 	else if (IsA(plan, MergeAppend))
-		dpns->outer_plan = linitial(((MergeAppend *) plan)->mergeplans);
+		dpns->outer_plan = linitial(((MergeAppend *) plan)->ap.subplans);
 	else
 		dpns->outer_plan = outerPlan(plan);
 
@@ -7955,10 +7955,10 @@ resolve_special_varno(Node *node, deparse_context *context,
 
 		if (IsA(dpns->plan, Append))
 			context->appendparents = bms_union(context->appendparents,
-											   ((Append *) dpns->plan)->apprelids);
+											   ((Append *) dpns->plan)->ap.apprelids);
 		else if (IsA(dpns->plan, MergeAppend))
 			context->appendparents = bms_union(context->appendparents,
-											   ((MergeAppend *) dpns->plan)->apprelids);
+											   ((MergeAppend *) dpns->plan)->ap.apprelids);
 
 		push_child_plan(dpns, dpns->outer_plan, &save_dpns);
 		resolve_special_varno((Node *) tle->expr, context,
diff --git a/src/include/executor/execAppend.h b/src/include/executor/execAppend.h
new file mode 100644
index 00000000000..c1030dc5282
--- /dev/null
+++ b/src/include/executor/execAppend.h
@@ -0,0 +1,33 @@
+/*-------------------------------------------------------------------------
+ * execAppend.h
+ *		Support functions for MergeAppend and Append nodes.
+ *
+ * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *		src/include/executor/execAppend.h
+ *-------------------------------------------------------------------------
+ */
+
+#ifndef EXECAPPEND_H
+#define EXECAPPEND_H
+
+#include "nodes/execnodes.h"
+
+void		ExecInitAppender(AppenderState * state,
+							 Appender * node,
+							 EState *estate,
+							 int eflags,
+							 int first_partial_plan,
+							 int *first_valid_partial_plan);
+
+void		ExecEndAppender(AppenderState * node);
+
+void		ExecReScanAppender(AppenderState * node);
+
+void		ExecAppenderAsyncBegin(AppenderState * node);
+
+void		ExecAppenderAsyncEventWait(AppenderState * node, int timeout, uint32 wait_event_info);
+
+#endif							/* EXECAPPEND_H */
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 5887cbf4f16..69123a31bbd 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1472,6 +1472,27 @@ typedef struct ModifyTableState
 	List	   *mt_mergeJoinConditions;
 } ModifyTableState;
 
+typedef struct AppenderState
+{
+	PlanState	ps;				/* its first field is NodeTag */
+	PlanState **plans;			/* array of PlanStates for my inputs */
+	int			nplans;
+
+	/* Asynchronous execution state */
+	Bitmapset  *asyncplans;		/* asynchronous plans indexes */
+	int			nasyncplans;	/* # of asynchronous plans */
+	AsyncRequest **asyncrequests;	/* array of AsyncRequests */
+	TupleTableSlot **asyncresults;	/* unreturned results of async plans */
+	Bitmapset  *needrequest;	/* asynchronous plans needing a new request */
+	struct WaitEventSet *eventset;	/* WaitEventSet for file descriptor waits */
+
+	/* Partition pruning state */
+	struct PartitionPruneState *prune_state;
+	bool		valid_subplans_identified;
+	Bitmapset  *valid_subplans;
+	Bitmapset  *valid_asyncplans;	/* valid asynchronous plans indexes */
+}			AppenderState;
+
 /* ----------------
  *	 AppendState information
  *
@@ -1493,31 +1514,20 @@ struct PartitionPruneState;
 
 struct AppendState
 {
-	PlanState	ps;				/* its first field is NodeTag */
-	PlanState **appendplans;	/* array of PlanStates for my inputs */
-	int			as_nplans;
+	AppenderState as;
+
 	int			as_whichplan;
 	bool		as_begun;		/* false means need to initialize */
-	Bitmapset  *as_asyncplans;	/* asynchronous plans indexes */
-	int			as_nasyncplans; /* # of asynchronous plans */
-	AsyncRequest **as_asyncrequests;	/* array of AsyncRequests */
-	TupleTableSlot **as_asyncresults;	/* unreturned results of async plans */
-	int			as_nasyncresults;	/* # of valid entries in as_asyncresults */
-	bool		as_syncdone;	/* true if all synchronous plans done in
-								 * asynchronous mode, else false */
+	int			as_nasyncresults;	/* # of valid entries in asyncresults */
+	bool		as_syncdone;	/* all sync plans done in async mode? */
 	int			as_nasyncremain;	/* # of remaining asynchronous plans */
-	Bitmapset  *as_needrequest; /* asynchronous plans needing a new request */
-	struct WaitEventSet *as_eventset;	/* WaitEventSet used to configure file
-										 * descriptor wait events */
-	int			as_first_partial_plan;	/* Index of 'appendplans' containing
-										 * the first partial plan */
-	ParallelAppendState *as_pstate; /* parallel coordination info */
-	Size		pstate_len;		/* size of parallel coordination info */
-	struct PartitionPruneState *as_prune_state;
-	bool		as_valid_subplans_identified;	/* is as_valid_subplans valid? */
-	Bitmapset  *as_valid_subplans;
-	Bitmapset  *as_valid_asyncplans;	/* valid asynchronous plans indexes */
-	bool		(*choose_next_subplan) (AppendState *);
+	int			as_first_partial_plan;
+
+	/* Parallel append specific */
+	ParallelAppendState *as_pstate;
+	Size		pstate_len;
+
+	bool		(*choose_next_subplan) (struct AppendState *);
 };
 
 /* ----------------
@@ -1537,27 +1547,17 @@ struct AppendState
  */
 typedef struct MergeAppendState
 {
-	PlanState	ps;				/* its first field is NodeTag */
-	PlanState **mergeplans;		/* array of PlanStates for my inputs */
-	int			ms_nplans;
+	AppenderState ms;
+
 	int			ms_nkeys;
 	SortSupport ms_sortkeys;	/* array of length ms_nkeys */
 	TupleTableSlot **ms_slots;	/* array of length ms_nplans */
 	struct binaryheap *ms_heap; /* binary heap of slot indices */
 	bool		ms_initialized; /* are subplans started? */
-	Bitmapset  *ms_asyncplans;	/* asynchronous plans indexes */
-	int			ms_nasyncplans; /* # of asynchronous plans */
-	AsyncRequest **ms_asyncrequests;	/* array of AsyncRequests */
-	TupleTableSlot **ms_asyncresults;	/* unreturned results of async plans */
+
+	/* Merge-specific async tracking */
 	Bitmapset  *ms_has_asyncresults;	/* plans which have async results */
 	Bitmapset  *ms_asyncremain; /* remaining asynchronous plans */
-	Bitmapset  *ms_needrequest; /* asynchronous plans needing a new request */
-	struct WaitEventSet *ms_eventset;	/* WaitEventSet used to configure file
-										 * descriptor wait events */
-	struct PartitionPruneState *ms_prune_state;
-	bool		ms_valid_subplans_identified;	/* is ms_valid_subplans valid? */
-	Bitmapset  *ms_valid_subplans;
-	Bitmapset  *ms_valid_asyncplans;	/* valid asynchronous plans indexes */
 } MergeAppendState;
 
 /* Getters for AppendState and MergeAppendState */
@@ -1567,9 +1567,9 @@ GetAppendEventSet(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
 
 	if (IsA(ps, AppendState))
-		return ((AppendState *) ps)->as_eventset;
+		return ((AppendState *) ps)->as.eventset;
 	else
-		return ((MergeAppendState *) ps)->ms_eventset;
+		return ((MergeAppendState *) ps)->ms.eventset;
 }
 
 static inline Bitmapset *
@@ -1578,9 +1578,9 @@ GetNeedRequest(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
 
 	if (IsA(ps, AppendState))
-		return ((AppendState *) ps)->as_needrequest;
+		return ((AppendState *) ps)->as.needrequest;
 	else
-		return ((MergeAppendState *) ps)->ms_needrequest;
+		return ((MergeAppendState *) ps)->ms.needrequest;
 }
 
 /* Common part of classify_matching_subplans() for Append and MergeAppend */
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index c4393a94321..30c20e80b40 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -380,6 +380,20 @@ typedef struct ModifyTable
 
 struct PartitionPruneInfo;		/* forward reference to struct below */
 
+typedef struct Appender
+{
+	Plan		plan;			/* its first field is NodeTag */
+	Bitmapset  *apprelids;		/* RTIs of appendrel(s) formed by this node */
+	List	   *subplans;		/* List of Plans (formerly
+								 * appendplans/mergeplans) */
+
+	/*
+	 * Index into PlannedStmt.partPruneInfos and parallel lists in EState. Set
+	 * to -1 if no run-time pruning is used.
+	 */
+	int			part_prune_index;
+}			Appender;
+
 /* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
@@ -387,25 +401,16 @@ struct PartitionPruneInfo;		/* forward reference to struct below */
  */
 typedef struct Append
 {
-	Plan		plan;
-	/* RTIs of appendrel(s) formed by this node */
-	Bitmapset  *apprelids;
-	List	   *appendplans;
+	Appender	ap;
+
 	/* # of asynchronous plans */
 	int			nasyncplans;
 
 	/*
-	 * All 'appendplans' preceding this index are non-partial plans. All
-	 * 'appendplans' from this index onwards are partial plans.
+	 * All 'subplans' preceding this index are non-partial plans. All
+	 * 'subplans' from this index onwards are partial plans.
 	 */
 	int			first_partial_plan;
-
-	/*
-	 * Index into PlannedStmt.partPruneInfos and parallel lists in EState:
-	 * es_part_prune_states and es_part_prune_results. Set to -1 if no
-	 * run-time pruning is used.
-	 */
-	int			part_prune_index;
 } Append;
 
 /* ----------------
@@ -415,12 +420,7 @@ typedef struct Append
  */
 typedef struct MergeAppend
 {
-	Plan		plan;
-
-	/* RTIs of appendrel(s) formed by this node */
-	Bitmapset  *apprelids;
-
-	List	   *mergeplans;
+	Appender	ap;
 
 	/* these fields are just like the sort-key info in struct Sort: */
 
@@ -438,13 +438,6 @@ typedef struct MergeAppend
 
 	/* NULLS FIRST/LAST directions */
 	bool	   *nullsFirst pg_node_attr(array_size(numCols));
-
-	/*
-	 * Index into PlannedStmt.partPruneInfos and parallel lists in EState:
-	 * es_part_prune_states and es_part_prune_results. Set to -1 if no
-	 * run-time pruning is used.
-	 */
-	int			part_prune_index;
 } MergeAppend;
 
 /* ----------------
-- 
2.51.2

---

From: Alexander Pyhalov <[email-masked]>
Date: Thu, 18 Dec 2025 12:56:02 +0300

Hi.

> Should we use the same WAIT_EVENT_APPEND_READY or create a new wait

I'm not sure that new wait event is needed - for observability I think 
it's not critical
to distinguish Append and MergeAppend when they waited for foreign 
scans.  But also it's perhaps
doesn't do any harm to record specific wait event.

> duplicated code blocks that was almost the same and that didn't require

Overall I like new Appender node. Splitting code in this way really 
helps to avoid code duplication.
However, some similar code is still needed, because logic of getting new 
tuples is different.

Some minor issues I've noticed.
1) ExecReScanAppender()  sets node->needrequest to NULL. 
ExecReScanAppend() calls bms_free(node->as.needrequest) immediately 
after this. The same is true for ExecReScanMergeAppend(). We should move 
it to ExecReScanAppender().

2) In src/backend/executor/execAppend.c:
planstates are named  as mergeplans in ExecEndAppender(), perhaps, 
appendplans or subplans are better names.

ExecInitAppender() could use palloc_array() to allocate appendplanstates 
- as ExecInitMergeAppend().

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: "Matheus Alcantara" <[email-masked]>
Date: Fri, 19 Dec 2025 10:45:29 -0300

> doesn't do any harm to record specific wait event.
Ok, I think that we can keep this way for now and let's see if a new
wait event is really needed.

> However, some similar code is still needed, because logic of getting new 
Indeed. 

> it to ExecReScanAppender().
Fixed

> appendplans or subplans are better names.
Fixed

> - as ExecInitMergeAppend().
Fixed

From 214207ab5dc2c2cdde12f0cc2ea471f7cc54da80 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH v10 1/3] mark_async_capable(): subpath should match subplan

 
 				/*
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.51.2

From 952fef6e9f05f6609636e82b62dc0f9f4ece649f Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH v10 2/3] MergeAppend should support Async Foreign Scan
 subplans

---

 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append

 
+-- Test Merge Append
 
+-- Test Merge Append

+-- Test Merge Append

 

 /*

 
 
 /*

 

+		/*

 
-		/*
 
 		/*
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*

 typedef struct
 {
 
 	/*

 

 

 

From 4b08e19de2a52a479a3f3f8c5db6601770e4c3aa Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 16 Dec 2025 16:32:14 -0300
Subject: [PATCH v10 3/3] Create execAppend.c to avoid duplicated code on
 [Merge]Append

---
 src/backend/executor/execAppend.c       | 410 +++++++++++++++++++
 src/backend/executor/nodeAppend.c       | 497 +++++-------------------
 src/backend/executor/nodeMergeAppend.c  | 416 +++-----------------
 19 files changed, 720 insertions(+), 913 deletions(-)

 

 

index 00000000000..1ddf717cf95
@@ -0,0 +1,410 @@
+/*  Begin all of the subscans of an Appender node. */
+	appendplanstates = palloc0_array(PlanState *, nplans);
+ExecReScanAppender(AppenderState * node)
+		bms_free(node->needrequest);
+/*  Wait or poll for file descriptor events and fire callbacks. */
+	/* Wait until at least one event occurs. */
+	noccurred = WaitEventSetWait(node->eventset, timeout, occurred_event,
+/*  Begin executing async-capable subplans. */
+/*  Shuts down the subplans of an Appender node. */
+ExecEndAppender(AppenderState * node)
+	PlanState **subplans;
+	subplans = node->plans;
+		ExecEndNode(subplans[i]);

 
 
index dfbc7b510c4..5c39ee275d2 100644
 
 #include "postgres.h"

 

 
-	/*

 

 		/*

 
 		/*
 
 		/*

@@ -400,81 +251,22 @@ ExecAppend(PlanState *pstate)
 void
 
 void
 
-		/*
 
-		/*

@@ -501,7 +293,7 @@ ExecAppendEstimate(AppendState *node,
 
@@ -523,7 +315,7 @@ ExecAppendInitializeDSM(AppendState *node,
 
 	node->as_pstate = pstate;
 	node->choose_next_subplan = choose_next_subplan_for_leader;
@@ -541,7 +333,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 	ParallelAppendState *pstate = node->as_pstate;

@@ -554,7 +346,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 
@@ -572,7 +364,7 @@ choose_next_subplan_locally(AppendState *node)
 	int			nextplan;

@@ -587,33 +379,33 @@ choose_next_subplan_locally(AppendState *node)
 
 		whichplan = -1;
 	}

 
 	if (nextplan < 0)
 	{
@@ -637,10 +429,10 @@ choose_next_subplan_for_leader(AppendState *node)

 
 
@@ -652,18 +444,18 @@ choose_next_subplan_for_leader(AppendState *node)
 	else
 	{
 		/* Start with last subplan. */
-		node->as_whichplan = node->as_nplans - 1;
+		node->as_whichplan = node->as.nplans - 1;
 
 		/*
 
 			/*
 			 * Mark each invalid plan as finished to allow the loop below to
@@ -719,10 +511,10 @@ choose_next_subplan_for_worker(AppendState *node)
 	ParallelAppendState *pstate = node->as_pstate;

 
 
@@ -735,11 +527,11 @@ choose_next_subplan_for_worker(AppendState *node)
 
 		mark_invalid_subplans_as_finished(node);
 	}
@@ -759,7 +551,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	{
 		int			nextplan;
 
-		nextplan = bms_next_member(node->as_valid_subplans,
+		nextplan = bms_next_member(node->as.valid_subplans,
 								   pstate->pa_next_plan);
 		if (nextplan >= 0)
 		{
@@ -772,7 +564,7 @@ choose_next_subplan_for_worker(AppendState *node)
 			 * Try looping back to the first valid partial plan, if there is
 			 * one.  If there isn't, arrange to bail out below.
 			 */
-			nextplan = bms_next_member(node->as_valid_subplans,
+			nextplan = bms_next_member(node->as.valid_subplans,
 									   node->as_first_partial_plan - 1);
 			pstate->pa_next_plan =
 				nextplan < 0 ? node->as_whichplan : nextplan;
@@ -797,7 +589,7 @@ choose_next_subplan_for_worker(AppendState *node)

 	/*
@@ -806,7 +598,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	 */
 
 		if (nextplan >= 0)
@@ -848,16 +640,16 @@ mark_invalid_subplans_as_finished(AppendState *node)
 	Assert(node->as_pstate);

 
@@ -876,47 +668,25 @@ mark_invalid_subplans_as_finished(AppendState *node)

 

@@ -961,7 +731,7 @@ ExecAppendAsyncGetNext(AppendState *node, TupleTableSlot **result)
 
@@ -981,7 +751,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 	int			i;
 
@@ -994,17 +764,17 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)

@@ -1015,7 +785,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 
@@ -1031,105 +801,12 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 static void

 
 /* ----------------------------------------------------------------
@@ -1165,14 +842,14 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 	}

 	/*
 
@@ -1187,10 +864,10 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 static void
 classify_matching_subplans(AppendState *node)
 {
-	Assert(node->as_valid_subplans_identified);
+	Assert(node->as.valid_subplans_identified);
 
@@ -1199,8 +876,8 @@ classify_matching_subplans(AppendState *node)
 
index f1c267eb9eb..e1a207aeb85 100644
 
 #include "postgres.h"

 
-	/*
 
 	/*

 
 		/*
 
@@ -426,81 +293,21 @@ heap_compare_slots(Datum a, Datum b, void *arg)
 
 void
 
-	/*
 
@@ -519,10 +326,10 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -530,9 +337,9 @@ classify_matching_subplans(MergeAppendState *node)

@@ -545,39 +352,17 @@ classify_matching_subplans(MergeAppendState *node)
 static void

 
 
@@ -638,7 +423,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 
@@ -648,7 +433,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 	 */
 	needrequest = NULL;
 	i = -1;
-	while ((i = bms_next_member(node->ms_needrequest, i)) >= 0)
+	while ((i = bms_next_member(node->ms.needrequest, i)) >= 0)
 	{
 		if (!bms_is_member(i, node->ms_has_asyncresults))
 			needrequest = bms_add_member(needrequest, i);
@@ -661,13 +446,13 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 		return false;

 
 		/*
@@ -683,7 +468,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 
@@ -707,7 +492,7 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 	/* We should handle previous async result prior to getting new one */
 	Assert(!bms_is_member(areq->request_index, node->ms_has_asyncresults));
 
@@ -730,13 +515,13 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 
 	/*
 
@@ -749,101 +534,8 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 static void
 
+	ExecAppenderAsyncEventWait(&node->ms, -1 /* no timeout */ , WAIT_EVENT_APPEND_READY);
 
 	if (pathkeys != NIL)
 	{

 
 	/*
 
 		if (prunequal != NIL)

 
 	/*

 
 	/*
 
 		if (prunequal != NIL)

 	/*

 

 	/*

 	return (Plan *) aplan;
 }

 

 	/*

 	return (Plan *) mplan;
 }
 
 		case T_Append:
 			{
 
 		case T_MergeAppend:
 			{

 

 struct AppendState
 {
 
 /* ----------------

 

 
 
+typedef struct Appender
+{
 
 	/*
 
 /* ----------------

 
 
 /* ----------------
-- 
2.51.2

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 23 Dec 2025 11:50:39 +0300

Matheus Alcantara писал(а) 2025-12-19 16:45:
>>> +	noccurred = WaitEventSetWait(node->ms_eventset, -1 /* no timeout */ 
>>> ,
>>> occurred_event,

Hi.

I've looked through updated patch. Tested it (also with our fdw). 
Overall looks good.

In execAppend.c there's still reference to as_valid_subplans. Also we 
could perhaps use palloc0_array() in some more places, for example, for 
for state->asyncrequests and state->asyncresults.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: "Matheus Alcantara" <[email-masked]>
Date: Mon, 29 Dec 2025 10:43:00 -0300

> I've looked through updated patch. Tested it (also with our fdw). 
Thanks for testing.

> for state->asyncrequests and state->asyncresults.
Fixed on the new attached version.

--
Matheus Alcantara
EDB: https://www.enterprisedb.com

From 9c219a3fe386e6e250369804290864af2c043bed Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH v11 1/3] mark_async_capable(): subpath should match subplan

index f1a01cfc544..05fac693989 100644
 
 				/*
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.51.2

From fafe5f619ba3cee74de4c3951c1e62c5c7a7af92 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH v11 2/3] MergeAppend should support Async Foreign Scan
 subplans

---

 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append

 
+-- Test Merge Append
 
+-- Test Merge Append

+-- Test Merge Append

 
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index cdfe8e376f0..f7f7e33cee6 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5473,6 +5473,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>

 /*

 
 
 /*

 

+		/*

 
-		/*
 
 		/*
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*

 typedef struct
 {
index 05fac693989..fc0e5c62ea9 100644
 
 	/*

 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index ac0c7c36c56..b60b23fa4b9 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -821,6 +821,14 @@
   boot_val => 'true',
 },

 

 

From 2b29d2c646c6dce4d7b2e470ce629134eaafa9aa Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 16 Dec 2025 16:32:14 -0300
Subject: [PATCH v11 3/3] Create execAppend.c to avoid duplicated code on
 [Merge]Append

---
 src/backend/executor/execAppend.c       | 408 +++++++++++++++++++
 19 files changed, 718 insertions(+), 913 deletions(-)

 

 

index 00000000000..1e76248f2d7
@@ -0,0 +1,408 @@
+		 * subplan, we can fill valid_subplans immediately, preventing
+		state->asyncrequests = palloc0_array(AsyncRequest *, nplans);
+		state->asyncresults = palloc0_array(TupleTableSlot *, nplans);

 

 #include "postgres.h"

 

 
-	/*

 

 		/*

 
 		/*
 
 		/*

 
 void
 
-		/*
 
-		/*

 

 

 
 
 		whichplan = -1;
 	}

 
 	if (nextplan < 0)
 	{

 

 		/*
 
 			/*

 

 

 	/*
 
 		if (nextplan >= 0)

 

 

 

 

 

 
 	/*

 
 
 #include "postgres.h"

 
-	/*
 
 	/*

 
 		/*

 void
 
-	/*

 

 

 

 
 		/*

 
 	/*

index fc0e5c62ea9..a7b7e3d45e0 100644
 
 	if (pathkeys != NIL)
 	{

 
 	/*
 
 		if (prunequal != NIL)

 
 	/*

 
 	/*
 
 		if (prunequal != NIL)

 	/*

 

 	/*

 	return (Plan *) aplan;
 }

 

 	/*

 	return (Plan *) mplan;
 }
 
 		case T_Append:
 			{
 
 		case T_MergeAppend:
 			{

 

 struct AppendState
 {
 
 /* ----------------

 

 
 
+typedef struct Appender
+{
 
 	/*
 
 /* ----------------

 
 
 /* ----------------
-- 
2.51.2

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 30 Dec 2025 16:15:45 +0300

Hi.

Looks good. What do you think about classify_matching_subplans_common()? 
Should it stay where it is or should we hide it to
src/include/executor/execAppend.h ?
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: "Matheus Alcantara" <[email-masked]>
Date: Tue, 30 Dec 2025 12:04:45 -0300

> src/include/executor/execAppend.h ?
Yeah, sounds better to me to move classify_matching_subplans_common to
execAppend.h since it very specific for the MergeAppend and Append
execution. I've declared the function as static inline on execAppend.h
but I'm not sure if it's the best approach.

I've also wrote a proper commit message for this new version.

From 14a51e23a506dc7d412dc7130c26b679fed520b9 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:16:25 +0300
Subject: [PATCH v12 1/3] mark_async_capable(): subpath should match subplan

 
 				/*
 
 				/*
 
 				/*

 			/*
 
 			/*
-- 
2.51.2

From c13180f186a924d3ec6987ea8c14eeb61bab10d7 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH v12 2/3] MergeAppend should support Async Foreign Scan
 subplans

---

index 6066510c7c0..1b35990b4c0 100644
 
 DELETE FROM result_tbl;
+-- Test Merge Append
 
 DELETE FROM result_tbl;
+-- Test Merge Append

index 4f7ab2ed0ac..89188dff783 100644
@@ -3929,6 +3929,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
@@ -3952,6 +3957,20 @@ DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -3967,6 +3986,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4205,6 +4229,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

 
 
 /*

 
 
 /*

 

+		/*

 
-		/*
 
 		/*
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*
 
index 54931cd6e2a..e7d741a7699 100644
 
 typedef struct
 {
 
 	/*

 

 

 

From f26775222d238441a5bd2fa60757d09cf50fd2cd Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 16 Dec 2025 16:32:14 -0300
Subject: [PATCH v12 3/3] Common infrastructure to MergeAppend and Append nodes

This commit introduces the execAppend.c file to centralize executor
operations that can be shared between MergeAppend and Append nodes.

The logic for initializing and ending the nodes, as well as initializing
asynchronous execution, is very similar for both MergeAppend and Append.
To reduce redundancy, the duplicated code has been moved to execAppend.c
so that these nodes can reuse the common implementation.

The code responsible for actually fetching the tuples remains specific
to each node and was not refactored into execAppend.c to preserve the
unique execution requirements of each node type.
---
 contrib/pg_overexplain/pg_overexplain.c |   4 +-
 contrib/postgres_fdw/postgres_fdw.c     |   8 +-
 src/backend/commands/explain.c          |  26 +-
 src/backend/executor/Makefile           |   1 +
 src/backend/executor/execAmi.c          |   2 +-
 src/backend/executor/execAppend.c       | 409 +++++++++++++++++++
 src/backend/executor/execCurrent.c      |   4 +-
 src/backend/executor/execProcnode.c     |   8 +-
 src/backend/executor/meson.build        |   1 +
 src/backend/executor/nodeAppend.c       | 497 +++++-------------------
 src/backend/executor/nodeMergeAppend.c  | 416 +++-----------------
 src/backend/nodes/nodeFuncs.c           |   8 +-
 src/backend/optimizer/plan/createplan.c |  34 +-
 src/backend/optimizer/plan/setrefs.c    |  44 +--
 src/backend/optimizer/plan/subselect.c  |   4 +-
 src/backend/utils/adt/ruleutils.c       |   8 +-
 src/include/executor/execAppend.h       |  60 +++
 src/include/nodes/execnodes.h           | 105 ++---
 src/include/nodes/plannodes.h           |  45 +--
 19 files changed, 746 insertions(+), 938 deletions(-)
 create mode 100644 src/backend/executor/execAppend.c
 create mode 100644 src/include/executor/execAppend.h

 

 

index 00000000000..b7222ab7940

 

 #include "postgres.h"

 

 
-	/*

 

 		/*

 
 		/*
 
 		/*

 
 void
 
-		/*
 
-		/*

 

 

 
 
 		whichplan = -1;
 	}

 
 	if (nextplan < 0)
 	{

 

 		/*
 
 			/*

 

 

 	/*
 
 		if (nextplan >= 0)

 

 

 

 

 

 
 	/*

 
 
 #include "postgres.h"

 
-	/*
 
 	/*

 
 		/*

 void
 
-	/*

 

 

 

 
 		/*

 
 	/*

 
 	if (pathkeys != NIL)
 	{

 
 	/*
 
 		if (prunequal != NIL)

 
 	/*

 
 	/*
 
 		if (prunequal != NIL)

 	/*

 

 	/*

 	return (Plan *) aplan;
 }

 

 	/*

 	return (Plan *) mplan;
 }
 
 		case T_Append:
 			{
 
 		case T_MergeAppend:
 			{

 
index 00000000000..b5509373524
@@ -0,0 +1,60 @@
+void		ExecAppenderAsyncEventWait(AppenderState * node,
+									   int timeout,
+									   uint32 wait_event_info);
index 5887cbf4f16..501f2c3acf4 100644

 struct AppendState
 {
 
 /* ----------------

 
 static inline Bitmapset *
@@ -1578,34 +1578,9 @@ GetNeedRequest(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));
 
 	if (IsA(ps, AppendState))
-		return ((AppendState *) ps)->as_needrequest;
+		return ((AppendState *) ps)->as.needrequest;
 	else
-		return ((MergeAppendState *) ps)->ms_needrequest;
-}
-
-/* Common part of classify_matching_subplans() for Append and MergeAppend */
-static inline bool
-classify_matching_subplans_common(Bitmapset **valid_subplans,
-								  Bitmapset *asyncplans,
-								  Bitmapset **valid_asyncplans)
-{
-	Assert(*valid_asyncplans == NULL);
-
-	/* Checked by classify_matching_subplans() */
-	Assert(!bms_is_empty(*valid_subplans));
-
-	/* Nothing to do if there are no valid async subplans. */
-	if (!bms_overlap(*valid_subplans, asyncplans))
-		return false;
-
-	/* Get valid async subplans. */
-	*valid_asyncplans = bms_intersect(asyncplans,
-									  *valid_subplans);
-
-	/* Adjust the valid subplans to contain sync subplans only. */
-	*valid_subplans = bms_del_members(*valid_subplans,
-									  *valid_asyncplans);
-	return true;
+		return ((MergeAppendState *) ps)->ms.needrequest;
 }
 
 /* ----------------

+typedef struct Appender
+{
 
 	/*
 
 /* ----------------

 
 
 /* ----------------
-- 
2.51.2

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 30 Dec 2025 22:04:21 +0300

> I've also wrote a proper commit message for this new version.

Looks good to me.

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: Alexander Pyhalov <[email-masked]>
Date: Thu, 12 Feb 2026 10:08:45 +0300

>> I've also wrote a proper commit message for this new version.

Hi.
Rebased patches over fresh master.

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From 5f2e5f89987384495ab53e7f7e79316ff1322814 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Thu, 12 Feb 2026 09:17:38 +0300
Subject: [PATCH 1/3] mark_async_capable(): subpath should match subplan

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 959df43c39e..09aba8a4bcf 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1137,10 +1137,12 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
 
 				/*
@@ -1158,10 +1160,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
 
 				Assert(fdwroutine != NULL);
@@ -1174,9 +1176,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 
 			/*
-- 
2.43.0

From 4f52e920ac368a485fb2990b83e06c3665165fa0 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH 2/3] MergeAppend should support Async Foreign Scan subplans

---

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 2ccb72c539a..bc11f35e1bc 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11567,6 +11567,46 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -11615,6 +11655,76 @@ COPY async_pt TO stdout; --error
@@ -11650,6 +11760,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -12432,6 +12573,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
index 3572689e33b..60e8b6e7d7f 100644

index 72d2d9c311b..c9560fa89a5 100644
@@ -3936,6 +3936,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
@@ -3959,6 +3964,20 @@ DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -3974,6 +3993,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4212,6 +4236,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 6bc2690ce07..1748369e617 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5534,6 +5534,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
index 8728111355d..e7c77f3cd2a 100644
 
 /*
index 7138dc692c6..b5619d52129 100644

index 30bfeaf7c13..39810691ba4 100644

 /*

 

+		/*

 
-		/*
 
 		/*
 
 	return result;
@@ -355,6 +447,7 @@ void
 
 	/*
 
index 89ca4e08bf1..298ea570dfb 100644
 
 typedef struct
 {
diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 09aba8a4bcf..f1f1759c3a5 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1465,6 +1465,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	List	   *subplans = NIL;
 	ListCell   *subpaths;
 	RelOptInfo *rel = best_path->path.parent;
+	bool		consider_async = false;
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1480,6 +1481,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	node->apprelids = rel->relids;
 	node->child_append_relid_sets = best_path->child_append_relid_sets;

 
diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index 271c033952e..e1c90ce69ea 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -821,6 +821,14 @@
   boot_val => 'true',
 },
 
index f938cc65a3a..db15c7b9870 100644
@@ -410,6 +410,7 @@
 
index dfcf45099ba..2255cc68b21 100644
 
index f8053d9e572..282747ee17b 100644
@@ -1547,10 +1547,69 @@ typedef struct MergeAppendState
 
index f2fd5d31507..798af1fcd5c 100644
 
index 3dd63fd88ed..3dcd9b17889 100644

From 4fb8074a1135aa94f719007fec06de689bf2eac9 Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 30 Dec 2025 14:32:20 +0300
Subject: [PATCH 3/3] Common infrastructure to MergeAppend and Append nodes

 contrib/pg_overexplain/pg_overexplain.c |   8 +-
 src/backend/optimizer/plan/createplan.c |  38 +-
 src/backend/optimizer/plan/setrefs.c    |  48 +--
 src/include/nodes/plannodes.h           |  56 +--
 19 files changed, 752 insertions(+), 954 deletions(-)

diff --git a/contrib/pg_overexplain/pg_overexplain.c b/contrib/pg_overexplain/pg_overexplain.c
index 36e6aac0e2c..e8cb2a33d3e 100644
--- a/contrib/pg_overexplain/pg_overexplain.c
+++ b/contrib/pg_overexplain/pg_overexplain.c
@@ -232,18 +232,18 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
 				break;
 			case T_Append:
 				overexplain_bitmapset("Append RTIs",
-									  ((Append *) plan)->apprelids,
+									  ((Append *) plan)->ap.apprelids,
 									  es);
 				overexplain_bitmapset_list("Child Append RTIs",
-										   ((Append *) plan)->child_append_relid_sets,
+										   ((Append *) plan)->ap.child_append_relid_sets,
 										   es);
 				break;
 			case T_MergeAppend:
 				overexplain_bitmapset("Append RTIs",
-									  ((MergeAppend *) plan)->apprelids,
+									  ((MergeAppend *) plan)->ap.apprelids,
 									  es);
 				overexplain_bitmapset_list("Child Append RTIs",
-										   ((MergeAppend *) plan)->child_append_relid_sets,
+										   ((MergeAppend *) plan)->ap.child_append_relid_sets,
 										   es);
 				break;
 			case T_Result:
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 60e8b6e7d7f..6ec28b27b42 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -2412,8 +2412,8 @@ find_modifytable_subplan(PlannerInfo *root,
 	{
 		Append	   *appendplan = (Append *) subplan;

 
index b7bb111688c..df65274e6f4 100644
@@ -1226,11 +1226,11 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
@@ -1274,7 +1274,7 @@ plan_is_disabled(Plan *plan)
 
@@ -1291,7 +1291,7 @@ plan_is_disabled(Plan *plan)
 
@@ -2338,13 +2338,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_Append:
@@ -2388,13 +2388,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
@@ -2608,7 +2608,7 @@ static void
 
index 90a68c0d156..18b70bf7063 100644
 
index 99f2b2d0c6f..37f5c7fd2c5 100644

index 7e40b852517..b99480f43fc 100644

index dc45be0b2ce..06191b22142 100644
index b5619d52129..2b77fc94f18 100644
 
 #include "postgres.h"

 

 
-	/*

 

 		/*

 
 		/*
 
 		/*

 
 void
 
-		/*
 
-		/*

 

 

 
 
 		whichplan = -1;
 	}

 
 	if (nextplan < 0)
 	{

 

 		/*
 
 			/*

 

 

 	/*
 
 		if (nextplan >= 0)

 

 

 

 

 

 
 	/*

 
index 39810691ba4..402d9a47681 100644
 
 #include "postgres.h"

 
-	/*
 
 	/*

 
 		/*

 void
 
-	/*

 

 

 

 
 		/*

 
 	/*

index 199ed27995f..608195a89fa 100644
@@ -4754,14 +4754,14 @@ planstate_tree_walker_impl(PlanState *planstate,
index f1f1759c3a5..5d5a83a1026 100644
@@ -1260,12 +1260,12 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
-	plan->child_append_relid_sets = best_path->child_append_relid_sets;
+	plan->ap.child_append_relid_sets = best_path->child_append_relid_sets;
 
 	if (pathkeys != NIL)
 	{
@@ -1284,7 +1284,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 										  &nodeSortOperators,
 										  &nodeCollations,
 										  &nodeNullsFirst);
-		tlist_was_changed = (orig_tlist_length != list_length(plan->plan.targetlist));
+		tlist_was_changed = (orig_tlist_length != list_length(plan->ap.plan.targetlist));
 	}
 
 	/* If appropriate, consider async append */
@@ -1394,7 +1394,7 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 	}

 	/*
 	 * If any quals exist, they may be useful to perform further partition
@@ -1419,16 +1419,16 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 		}
 
 		if (prunequal != NIL)

 
 	/*
 	 * If prepare_sort_from_pathkeys added sort columns, but we were told to
@@ -1437,9 +1437,9 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 	 */
 	if (tlist_was_changed && (flags & (CP_EXACT_TLIST | CP_SMALL_TLIST)))
 	{
-		tlist = list_copy_head(plan->plan.targetlist, orig_tlist_length);
+		tlist = list_copy_head(plan->ap.plan.targetlist, orig_tlist_length);
 		return inject_projection_plan((Plan *) plan, tlist,
-									  plan->plan.parallel_safe);
+									  plan->ap.plan.parallel_safe);
 	}
 	else
 		return (Plan *) plan;
@@ -1457,7 +1457,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 						 int flags)
 {
 	MergeAppend *node = makeNode(MergeAppend);
-	Plan	   *plan = &node->plan;
+	Plan	   *plan = &node->ap.plan;
 	List	   *tlist = build_path_tlist(root, &best_path->path);
 	int			orig_tlist_length = list_length(tlist);
 	bool		tlist_was_changed;
@@ -1478,8 +1478,8 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	plan->qual = NIL;
 	plan->lefttree = NULL;
 	plan->righttree = NULL;
-	node->apprelids = rel->relids;
-	node->child_append_relid_sets = best_path->child_append_relid_sets;
+	node->ap.apprelids = rel->relids;
+	node->ap.child_append_relid_sets = best_path->child_append_relid_sets;

 
 	/*
 
 		if (prunequal != NIL)

 	/*
index 5ad6c13830b..40f925c5f6b 100644
@@ -1880,10 +1880,10 @@ set_append_references(PlannerInfo *root,
 
@@ -1896,11 +1896,11 @@ set_append_references(PlannerInfo *root,
 
 			Plan	   *result;
 
@@ -1908,7 +1908,7 @@ set_append_references(PlannerInfo *root,
 
 			/* Remember that we removed an Append */
 			record_elided_node(root->glob, p->plan_node_id, T_Append,
-							   offset_relid_set(aplan->apprelids, rtoffset));
+							   offset_relid_set(aplan->ap.apprelids, rtoffset));
 
 			return result;
 		}
@@ -1921,19 +1921,19 @@ set_append_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) aplan, rtoffset);

 	/*

 	return (Plan *) aplan;
 }
@@ -1957,10 +1957,10 @@ set_mergeappend_references(PlannerInfo *root,
 
@@ -1974,11 +1974,11 @@ set_mergeappend_references(PlannerInfo *root,
 
 			Plan	   *result;
 
@@ -1986,7 +1986,7 @@ set_mergeappend_references(PlannerInfo *root,
 
 			/* Remember that we removed a MergeAppend */
 			record_elided_node(root->glob, p->plan_node_id, T_MergeAppend,
-							   offset_relid_set(mplan->apprelids, rtoffset));
+							   offset_relid_set(mplan->ap.apprelids, rtoffset));
 
 			return result;
 		}
@@ -1999,19 +1999,19 @@ set_mergeappend_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) mplan, rtoffset);

 	/*

 	return (Plan *) mplan;
 }
index e9dc9d31f05..525e759de9e 100644
 
 		case T_Append:
 			{
 
 		case T_MergeAppend:
 			{
index b5a7ad9066e..de292f28f17 100644

 
index 282747ee17b..26a0e1749e3 100644
@@ -1474,6 +1474,27 @@ typedef struct ModifyTableState
 
@@ -1495,31 +1516,20 @@ struct PartitionPruneState;
 
 struct AppendState
 {
 
 /* ----------------
@@ -1539,27 +1549,17 @@ struct AppendState
  */
 
 /* Getters for AppendState and MergeAppendState */
@@ -1569,9 +1569,9 @@ GetAppendEventSet(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));

 static inline Bitmapset *
@@ -1580,34 +1580,9 @@ GetNeedRequest(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));

 /* ----------------
diff --git a/src/include/nodes/plannodes.h b/src/include/nodes/plannodes.h
index 485bec5aabd..d546a02b94e 100644
--- a/src/include/nodes/plannodes.h
+++ b/src/include/nodes/plannodes.h
@@ -386,6 +386,22 @@ typedef struct ModifyTable

+typedef struct Appender
+{
+	Plan		plan;			/* its first field is NodeTag */
+	Bitmapset  *apprelids;		/* RTIs of appendrel(s) formed by this node */
+	List	   *child_append_relid_sets;	/* sets of RTIs of appendrels
+											 * consolidated into this node */
+	List	   *subplans;		/* List of Plans (formerly
+								 * appendplans/mergeplans) */
+
+	/*
+	 * Index into PlannedStmt.partPruneInfos and parallel lists in EState. Set
+	 * to -1 if no run-time pruning is used.
+	 */
+	int			part_prune_index;
+}			Appender;
+
 /* ----------------
  *	 Append node -
  *		Generate the concatenation of the results of sub-plans.
@@ -393,32 +409,16 @@ struct PartitionPruneInfo;		/* forward reference to struct below */
  */
 typedef struct Append
 {
-	Plan		plan;
-
-	/* RTIs of appendrel(s) formed by this node */
-	Bitmapset  *apprelids;
-
-	/* sets of RTIs of appendrels consolidated into this node */
-	List	   *child_append_relid_sets;
-
-	/* plans to run */
-	List	   *appendplans;
+	Appender	ap;

 	/*
 
 /* ----------------
@@ -428,16 +428,7 @@ typedef struct Append
  */
 typedef struct MergeAppend
 {
-	Plan		plan;
-
-	/* RTIs of appendrel(s) formed by this node */
-	Bitmapset  *apprelids;
-
-	/* sets of RTIs of appendrels consolidated into this node */
-	List	   *child_append_relid_sets;
-
-	/* plans to run */
-	List	   *mergeplans;
+	Appender	ap;

@@ -455,13 +446,6 @@ typedef struct MergeAppend

 /* ----------------
-- 
2.43.0

---

From: Alexander Pyhalov <[email-masked]>
Date: Wed, 18 Mar 2026 09:17:15 +0300

Alexander Pyhalov писал(а) 2026-03-02 09:44:
> Alexander Pyhalov писал(а) 2026-02-12 10:08:

Hi.

-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

From d1f50696c83075def009a2870a765e4778c84b1d Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Thu, 12 Feb 2026 09:17:38 +0300
Subject: [PATCH 1/3] mark_async_capable(): subpath should match subplan

diff --git a/src/backend/optimizer/plan/createplan.c b/src/backend/optimizer/plan/createplan.c
index 50b0e10308b..5d704e38f37 100644
--- a/src/backend/optimizer/plan/createplan.c
+++ b/src/backend/optimizer/plan/createplan.c
@@ -1138,10 +1138,12 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				SubqueryScan *scan_plan = (SubqueryScan *) plan;
 
 				/*
 
 				/*
@@ -1159,10 +1161,10 @@ mark_async_capable_plan(Plan *plan, Path *path)
 				FdwRoutine *fdwroutine = path->parent->fdwroutine;
 
 				/*
 
 				Assert(fdwroutine != NULL);
@@ -1175,9 +1177,9 @@ mark_async_capable_plan(Plan *plan, Path *path)
 
 			/*
 
 			/*
-- 
2.43.0

From 02474f6c9b9152c5d08316cb08b8571e3d3b4191 Mon Sep 17 00:00:00 2001
From: Alexander Pyhalov <[email-masked]>
Date: Sat, 15 Nov 2025 10:23:47 +0300
Subject: [PATCH 2/3] MergeAppend should support Async Foreign Scan subplans

---

diff --git a/contrib/postgres_fdw/expected/postgres_fdw.out b/contrib/postgres_fdw/expected/postgres_fdw.out
index 0f5271d476e..e73db70ca69 100644
--- a/contrib/postgres_fdw/expected/postgres_fdw.out
+++ b/contrib/postgres_fdw/expected/postgres_fdw.out
@@ -11575,6 +11575,46 @@ SELECT * FROM result_tbl ORDER BY a;
 (2 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -11623,6 +11663,76 @@ COPY async_pt TO stdout; --error
@@ -11658,6 +11768,37 @@ SELECT * FROM result_tbl ORDER BY a;
 (3 rows)
 
 DELETE FROM result_tbl;
+-- Test Merge Append
@@ -12440,6 +12581,153 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
index 41e47cc795b..4d113050cda 100644
@@ -7214,12 +7214,16 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)

@@ -7257,7 +7261,7 @@ postgresForeignAsyncConfigureWait(AsyncRequest *areq)
index 49ed797e8ef..73fc5317ad5 100644
@@ -3943,6 +3943,11 @@ INSERT INTO result_tbl SELECT a, b, 'AAA' || c FROM async_pt WHERE b === 505;
 
+-- Test Merge Append
@@ -3966,6 +3971,20 @@ DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -3981,6 +4000,11 @@ INSERT INTO result_tbl SELECT * FROM async_pt WHERE b === 505;
 SELECT * FROM result_tbl ORDER BY a;
 DELETE FROM result_tbl;
 
+-- Test Merge Append
 
@@ -4219,6 +4243,69 @@ SELECT a FROM base_tbl WHERE (a, random() > 0) IN (SELECT a, random() > 0 FROM f
 DROP FOREIGN TABLE foreign_tbl CASCADE;
 DROP TABLE base_tbl;

diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 8cdd826fbd3..0577d5bc374 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -5556,6 +5556,20 @@ ANY <replaceable class="parameter">num_sync</replaceable> ( <replaceable class="
       </listitem>
      </varlistentry>
 
index cf7ddbb01f4..f839f5f255c 100644
@@ -18,6 +18,7 @@
 #include "executor/instrument.h"
 
 /*
@@ -122,6 +123,9 @@ ExecAsyncResponse(AsyncRequest *areq)
 		case T_AppendState:
index 85c85569b5e..55164e36ce3 100644
@@ -1189,10 +1189,7 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 
 	/* Nothing to do if there are no valid subplans. */
 	if (bms_is_empty(node->as_valid_subplans))
@@ -1202,21 +1199,10 @@ classify_matching_subplans(AppendState *node)
 		return;
 	}
 
index 72eebd50bdf..561a1ce3260 100644
@@ -39,11 +39,16 @@
 #include "postgres.h"
 
 #include "utils/sortsupport.h"
 
 /*
  * We have one slot for each item in the heap array.  We use SlotNumber
@@ -55,6 +60,12 @@ typedef int32 SlotNumber;
 static TupleTableSlot *ExecMergeAppend(PlanState *pstate);
 static int	heap_compare_slots(Datum a, Datum b, void *arg);

 /* ----------------------------------------------------------------
  *		ExecInitMergeAppend
@@ -72,6 +83,8 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	int			nplans;
 	int			i,
 				j;
+	Bitmapset  *asyncplans;
+	int			nasyncplans;
 
@@ -107,7 +120,10 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
@@ -120,6 +136,7 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 
@@ -136,11 +153,25 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	 * the results into the mergeplanstates array.
 	 */
 	j = 0;
+	asyncplans = NULL;
+	nasyncplans = 0;
+
 	i = -1;
 	while ((i = bms_next_member(validsubplans, i)) >= 0)
 	{
 		Plan	   *initNode = (Plan *) list_nth(node->mergeplans, i);
 
+		/*
 
@@ -171,6 +202,45 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 	 */
 	mergestate->ps.ps_ProjInfo = NULL;
 
@@ -227,14 +297,18 @@ ExecMergeAppend(PlanState *pstate)
 
-		/*
 
 		/*
@@ -247,6 +321,16 @@ ExecMergeAppend(PlanState *pstate)
@@ -261,7 +345,13 @@ ExecMergeAppend(PlanState *pstate)
@@ -277,6 +367,8 @@ ExecMergeAppend(PlanState *pstate)
 
 	return result;
@@ -356,6 +448,7 @@ void
 
 	/*
@@ -366,8 +459,11 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -388,6 +484,367 @@ ExecReScanMergeAppend(MergeAppendState *node)
index 56d45287c89..dc9d2c31a81 100644
@@ -164,6 +164,7 @@ bool		enable_parallel_hash = true;
 
 typedef struct
 {
index 5d704e38f37..5a3fc0d281b 100644
 
 	/*
 	 * We don't have the actual creation of the MergeAppend node split out
@@ -1481,6 +1482,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	node->apprelids = rel->relids;
 	node->child_append_relid_sets = best_path->child_append_relid_sets;
 
@@ -1581,6 +1586,10 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 			subplan = sort_plan;
 		}

diff --git a/src/backend/utils/misc/guc_parameters.dat b/src/backend/utils/misc/guc_parameters.dat
index a5a0edf2534..e736479626b 100644
--- a/src/backend/utils/misc/guc_parameters.dat
+++ b/src/backend/utils/misc/guc_parameters.dat
@@ -821,6 +821,14 @@
   boot_val => 'true',
 },
 
index e686d88afc4..734302353ff 100644

index 0716c5a9aed..0749e96c947 100644
@@ -1557,10 +1557,69 @@ typedef struct MergeAppendState

 extern double index_pages_fetched(double tuples_fetched, BlockNumber pages,
diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out
index 132b56a5864..422ca8b7d1f 100644
--- a/src/test/regress/expected/sysviews.out
+++ b/src/test/regress/expected/sysviews.out
@@ -156,6 +156,7 @@ select name, setting from pg_settings where name like 'enable%';
               name              | setting 
 --------------------------------+---------
  enable_async_append            | on
+ enable_async_merge_append      | on
  enable_bitmapscan              | on
  enable_distinct_reordering     | on
  enable_eager_aggregate         | on
@@ -180,7 +181,7 @@ select name, setting from pg_settings where name like 'enable%';
  enable_seqscan                 | on
  enable_sort                    | on
  enable_tidscan                 | on
-(25 rows)
+(26 rows)

From 9b471681819b9e074a60af291e9f7823eb84c036 Mon Sep 17 00:00:00 2001
From: Matheus Alcantara <[email-masked]>
Date: Tue, 30 Dec 2025 14:32:20 +0300
Subject: [PATCH 3/3] Common infrastructure to MergeAppend and Append nodes

 contrib/pg_plan_advice/pgpa_scan.c      |   4 +-
 contrib/pg_plan_advice/pgpa_walker.c    |   8 +-
 src/backend/executor/nodeAppend.c       | 496 +++++-------------------
 21 files changed, 758 insertions(+), 959 deletions(-)

diff --git a/contrib/pg_overexplain/pg_overexplain.c b/contrib/pg_overexplain/pg_overexplain.c
index c2b90493cc6..7361834c544 100644
--- a/contrib/pg_overexplain/pg_overexplain.c
+++ b/contrib/pg_overexplain/pg_overexplain.c
@@ -232,18 +232,18 @@ overexplain_per_node_hook(PlanState *planstate, List *ancestors,
 				break;
 			case T_Append:
 				overexplain_bitmapset("Append RTIs",
-									  ((Append *) plan)->apprelids,
+									  ((Append *) plan)->ap.apprelids,
 									  es);
 				overexplain_bitmapset_list("Child Append RTIs",
-										   ((Append *) plan)->child_append_relid_sets,
+										   ((Append *) plan)->ap.child_append_relid_sets,
 										   es);
 				break;
 			case T_MergeAppend:
 				overexplain_bitmapset("Append RTIs",
-									  ((MergeAppend *) plan)->apprelids,
+									  ((MergeAppend *) plan)->ap.apprelids,
 									  es);
 				overexplain_bitmapset_list("Child Append RTIs",
-										   ((MergeAppend *) plan)->child_append_relid_sets,
+										   ((MergeAppend *) plan)->ap.child_append_relid_sets,
 										   es);
 				break;
 			case T_Result:
diff --git a/contrib/pg_plan_advice/pgpa_scan.c b/contrib/pg_plan_advice/pgpa_scan.c
index 5f210f2b725..18b4ef0fb03 100644
--- a/contrib/pg_plan_advice/pgpa_scan.c
+++ b/contrib/pg_plan_advice/pgpa_scan.c
@@ -142,7 +142,7 @@ pgpa_build_scan(pgpa_plan_walker_context *walker, Plan *plan,
 
 				/* Be sure to account for pulled-up scans. */
 				child_append_relid_sets =
-					((Append *) plan)->child_append_relid_sets;
+					((Append *) plan)->ap.child_append_relid_sets;
 				break;
 			case T_MergeAppend:
 				/* Same logic here as for Append, above. */
@@ -154,7 +154,7 @@ pgpa_build_scan(pgpa_plan_walker_context *walker, Plan *plan,
 
 				/* Be sure to account for pulled-up scans. */
 				child_append_relid_sets =
-					((MergeAppend *) plan)->child_append_relid_sets;
+					((MergeAppend *) plan)->ap.child_append_relid_sets;
 				break;
 			default:
 				strategy = PGPA_SCAN_ORDINARY;
diff --git a/contrib/pg_plan_advice/pgpa_walker.c b/contrib/pg_plan_advice/pgpa_walker.c
index 7b86cc5e6f9..6cbade59553 100644
--- a/contrib/pg_plan_advice/pgpa_walker.c
+++ b/contrib/pg_plan_advice/pgpa_walker.c
@@ -409,14 +409,14 @@ pgpa_walk_recursively(pgpa_plan_walker_context *walker, Plan *plan,
 			{
 				Append	   *aplan = (Append *) plan;
 
-				extraplans = aplan->appendplans;
+				extraplans = aplan->ap.subplans;
 			}
 			break;
 		case T_MergeAppend:
 			{
 				MergeAppend *maplan = (MergeAppend *) plan;
 
-				extraplans = maplan->mergeplans;
+				extraplans = maplan->ap.subplans;
 			}
 			break;
 		case T_BitmapAnd:
@@ -539,9 +539,9 @@ pgpa_relids(Plan *plan)
 	else if (IsA(plan, ForeignScan))
 		return ((ForeignScan *) plan)->fs_relids;
 	else if (IsA(plan, Append))
-		return ((Append *) plan)->apprelids;
+		return ((Append *) plan)->ap.apprelids;
 	else if (IsA(plan, MergeAppend))
-		return ((MergeAppend *) plan)->apprelids;
+		return ((MergeAppend *) plan)->ap.apprelids;
 
 	return NULL;
 }
diff --git a/contrib/postgres_fdw/postgres_fdw.c b/contrib/postgres_fdw/postgres_fdw.c
index 4d113050cda..b7444fdb22e 100644
--- a/contrib/postgres_fdw/postgres_fdw.c
+++ b/contrib/postgres_fdw/postgres_fdw.c
@@ -2413,8 +2413,8 @@ find_modifytable_subplan(PlannerInfo *root,
 	{
 		Append	   *appendplan = (Append *) subplan;
 
@@ -2422,8 +2422,8 @@ find_modifytable_subplan(PlannerInfo *root,

index 296ea8a1ed2..7dae636fff9 100644
@@ -1228,11 +1228,11 @@ ExplainPreScanNode(PlanState *planstate, Bitmapset **rels_used)
@@ -1276,7 +1276,7 @@ plan_is_disabled(Plan *plan)
 
@@ -1293,7 +1293,7 @@ plan_is_disabled(Plan *plan)
 
@@ -2340,13 +2340,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
 	switch (nodeTag(plan))
 	{
 		case T_Append:
@@ -2390,13 +2390,13 @@ ExplainNode(PlanState *planstate, List *ancestors,
@@ -2610,7 +2610,7 @@ static void
 
index 37fe03fdc37..23cb2f82281 100644
@@ -538,7 +538,7 @@ ExecSupportsBackwardScan(Plan *node)

 
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index d35976925ae..8282e86635b 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -911,8 +911,8 @@ ExecSetTupleBound(int64 tuples_needed, PlanState *child_node)
 		AppendState *aState = (AppendState *) child_node;
 		int			i;
 
@@ -924,8 +924,8 @@ ExecSetTupleBound(int64 tuples_needed, PlanState *child_node)
 
index 55164e36ce3..975ae87a036 100644
@@ -57,6 +57,7 @@
 
 #include "postgres.h"
 
@@ -111,15 +112,6 @@ AppendState *
 
@@ -127,167 +119,27 @@ ExecInitAppend(Append *node, EState *estate, int eflags)

 
-	/*

 	/* For parallel query, this will be overridden later. */
 	appendstate->choose_next_subplan = choose_next_subplan_locally;
@@ -317,11 +169,11 @@ ExecAppend(PlanState *pstate)
 		Assert(!node->as_syncdone);

 
 		/*
@@ -329,11 +181,11 @@ ExecAppend(PlanState *pstate)
 		 * proceeding.
 		 */
 		if (!node->choose_next_subplan(node) && node->as_nasyncremain == 0)
-			return ExecClearTuple(node->ps.ps_ResultTupleSlot);
+			return ExecClearTuple(node->as.ps.ps_ResultTupleSlot);

@@ -348,19 +200,19 @@ ExecAppend(PlanState *pstate)
 
 		/*
 
 		/*
 		 * get a tuple from the subplan
@@ -387,7 +239,7 @@ ExecAppend(PlanState *pstate)

@@ -402,81 +254,22 @@ ExecAppend(PlanState *pstate)
 void
 
 void
 
-		/*
 
-		/*

@@ -503,7 +296,7 @@ ExecAppendEstimate(AppendState *node,
 
@@ -525,7 +318,7 @@ ExecAppendInitializeDSM(AppendState *node,
 
 	node->as_pstate = pstate;
 	node->choose_next_subplan = choose_next_subplan_for_leader;
@@ -543,7 +336,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 	ParallelAppendState *pstate = node->as_pstate;

@@ -556,7 +349,7 @@ ExecAppendReInitializeDSM(AppendState *node, ParallelContext *pcxt)
 
@@ -574,7 +367,7 @@ choose_next_subplan_locally(AppendState *node)
 	int			nextplan;

@@ -589,33 +382,33 @@ choose_next_subplan_locally(AppendState *node)
 
 		whichplan = -1;
 	}

 
 	if (nextplan < 0)
 	{
@@ -639,10 +432,10 @@ choose_next_subplan_for_leader(AppendState *node)

 
 
@@ -654,18 +447,18 @@ choose_next_subplan_for_leader(AppendState *node)
 	else
 	{
 		/* Start with last subplan. */
-		node->as_whichplan = node->as_nplans - 1;
+		node->as_whichplan = node->as.nplans - 1;
 
 		/*
 
 			/*
 			 * Mark each invalid plan as finished to allow the loop below to
@@ -721,10 +514,10 @@ choose_next_subplan_for_worker(AppendState *node)
 	ParallelAppendState *pstate = node->as_pstate;

 
 
@@ -737,11 +530,11 @@ choose_next_subplan_for_worker(AppendState *node)
 
 		mark_invalid_subplans_as_finished(node);
 	}
@@ -761,7 +554,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	{
 		int			nextplan;
 
-		nextplan = bms_next_member(node->as_valid_subplans,
+		nextplan = bms_next_member(node->as.valid_subplans,
 								   pstate->pa_next_plan);
 		if (nextplan >= 0)
 		{
@@ -774,7 +567,7 @@ choose_next_subplan_for_worker(AppendState *node)
 			 * Try looping back to the first valid partial plan, if there is
 			 * one.  If there isn't, arrange to bail out below.
 			 */
-			nextplan = bms_next_member(node->as_valid_subplans,
+			nextplan = bms_next_member(node->as.valid_subplans,
 									   node->as_first_partial_plan - 1);
 			pstate->pa_next_plan =
 				nextplan < 0 ? node->as_whichplan : nextplan;
@@ -799,7 +592,7 @@ choose_next_subplan_for_worker(AppendState *node)

 	/*
@@ -808,7 +601,7 @@ choose_next_subplan_for_worker(AppendState *node)
 	 */
 
 		if (nextplan >= 0)
@@ -850,16 +643,16 @@ mark_invalid_subplans_as_finished(AppendState *node)
 	Assert(node->as_pstate);

 
@@ -878,47 +671,25 @@ mark_invalid_subplans_as_finished(AppendState *node)

 

@@ -963,7 +734,7 @@ ExecAppendAsyncGetNext(AppendState *node, TupleTableSlot **result)
 
@@ -983,7 +754,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 	int			i;
 
@@ -996,17 +767,17 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)

@@ -1017,7 +788,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 
@@ -1033,105 +804,12 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 static void

 
 /* ----------------------------------------------------------------
@@ -1167,14 +845,14 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 	}

 	/*
 
@@ -1189,10 +867,10 @@ ExecAsyncAppendResponse(AsyncRequest *areq)
 static void
 classify_matching_subplans(AppendState *node)
 {
-	Assert(node->as_valid_subplans_identified);
+	Assert(node->as.valid_subplans_identified);
 
@@ -1201,8 +879,8 @@ classify_matching_subplans(AppendState *node)
 
index 561a1ce3260..3d4d8386177 100644
 
 #include "postgres.h"
 
@@ -77,14 +78,7 @@ MergeAppendState *
 
@@ -92,154 +86,27 @@ ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
 
-	/*
 
 	/*
@@ -294,20 +161,20 @@ ExecMergeAppend(PlanState *pstate)

 
 		/*
@@ -315,16 +182,16 @@ ExecMergeAppend(PlanState *pstate)
 		 * and set up the heap.
 		 */
 		i = -1;
 
@@ -345,12 +212,12 @@ ExecMergeAppend(PlanState *pstate)
@@ -361,7 +228,7 @@ ExecMergeAppend(PlanState *pstate)
@@ -427,81 +294,21 @@ heap_compare_slots(Datum a, Datum b, void *arg)
 
 void
 
-	/*
 
@@ -520,10 +327,10 @@ ExecReScanMergeAppend(MergeAppendState *node)
 
@@ -531,9 +338,9 @@ classify_matching_subplans(MergeAppendState *node)

@@ -546,39 +353,17 @@ classify_matching_subplans(MergeAppendState *node)
 static void

 
 
@@ -639,7 +424,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 
@@ -649,7 +434,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 	 */
 	needrequest = NULL;
 	i = -1;
-	while ((i = bms_next_member(node->ms_needrequest, i)) >= 0)
+	while ((i = bms_next_member(node->ms.needrequest, i)) >= 0)
 	{
 		if (!bms_is_member(i, node->ms_has_asyncresults))
 			needrequest = bms_add_member(needrequest, i);
@@ -662,13 +447,13 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 		return false;

 
 		/*
@@ -684,7 +469,7 @@ ExecMergeAppendAsyncRequest(MergeAppendState *node, int mplan)
 
@@ -708,7 +493,7 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 	/* We should handle previous async result prior to getting new one */
 	Assert(!bms_is_member(areq->request_index, node->ms_has_asyncresults));
 
@@ -731,13 +516,13 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 
 	/*
 
@@ -750,101 +535,8 @@ ExecAsyncMergeAppendResponse(AsyncRequest *areq)
 static void
 
index 6a850349cf7..5124e787b14 100644
@@ -4825,14 +4825,14 @@ planstate_tree_walker_impl(PlanState *planstate,
index 5a3fc0d281b..4ac24ffa3af 100644
@@ -1261,12 +1261,12 @@ create_append_plan(PlannerInfo *root, AppendPath *best_path, int flags)
 
 	if (pathkeys != NIL)
 	{

 
 	/*
 
 		if (prunequal != NIL)

 
 	/*
@@ -1479,8 +1479,8 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 
 	consider_async = (enable_async_merge_append &&
 					  !best_path->path.parallel_safe &&
@@ -1594,7 +1594,7 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 	}

 	/*
 	 * If any quals exist, they may be useful to perform further partition
@@ -1611,12 +1611,12 @@ create_merge_append_plan(PlannerInfo *root, MergeAppendPath *best_path,
 		Assert(best_path->path.param_info == NULL);
 
 		if (prunequal != NIL)

 	/*
index 1b5b9b5ed9c..0c1fc455423 100644
@@ -1881,10 +1881,10 @@ set_append_references(PlannerInfo *root,
 
@@ -1897,11 +1897,11 @@ set_append_references(PlannerInfo *root,

@@ -1909,7 +1909,7 @@ set_append_references(PlannerInfo *root,

 			return result;
 		}
@@ -1922,19 +1922,19 @@ set_append_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) aplan, rtoffset);

 	/*

 	return (Plan *) aplan;
 }
@@ -1958,10 +1958,10 @@ set_mergeappend_references(PlannerInfo *root,
 
@@ -1975,11 +1975,11 @@ set_mergeappend_references(PlannerInfo *root,

@@ -1987,7 +1987,7 @@ set_mergeappend_references(PlannerInfo *root,

 			return result;
 		}
@@ -2000,19 +2000,19 @@ set_mergeappend_references(PlannerInfo *root,
 	 */
 	set_dummy_tlist_references((Plan *) mplan, rtoffset);

 	/*

 	return (Plan *) mplan;
 }
diff --git a/src/backend/optimizer/plan/subselect.c b/src/backend/optimizer/plan/subselect.c
index 0d31861da7f..71a74aa645b 100644
--- a/src/backend/optimizer/plan/subselect.c
+++ b/src/backend/optimizer/plan/subselect.c
@@ -2904,7 +2904,7 @@ finalize_plan(PlannerInfo *root, Plan *plan,
 
 		case T_Append:
 			{
-				foreach(l, ((Append *) plan)->appendplans)
+				foreach(l, ((Append *) plan)->ap.subplans)
 				{
 					context.paramids =
 						bms_add_members(context.paramids,
@@ -2919,7 +2919,7 @@ finalize_plan(PlannerInfo *root, Plan *plan,
 
 		case T_MergeAppend:
 			{
index 7bc12589e40..36a7d736fda 100644
@@ -5520,9 +5520,9 @@ set_deparse_plan(deparse_namespace *dpns, Plan *plan)
 
@@ -8498,10 +8498,10 @@ resolve_special_varno(Node *node, deparse_context *context,

index 0749e96c947..42ff2a23767 100644
@@ -1484,6 +1484,27 @@ typedef struct ModifyTableState
 
@@ -1505,31 +1526,20 @@ struct PartitionPruneState;
 
 struct AppendState
 {
 
 /* ----------------
@@ -1549,27 +1559,17 @@ struct AppendState
  */
 
 /* Getters for AppendState and MergeAppendState */
@@ -1579,9 +1579,9 @@ GetAppendEventSet(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));

 static inline Bitmapset *
@@ -1590,34 +1590,9 @@ GetNeedRequest(PlanState *ps)
 	Assert(IsA(ps, AppendState) || IsA(ps, MergeAppendState));

 /* ----------------
index b6185825fcb..b0f61eaab5e 100644

+typedef struct Appender
+{

 	/*
 
 /* ----------------

 
 
 /* ----------------
-- 
2.43.0

---

From: Alexander Korotkov <[email-masked]>
Date: Mon, 30 Mar 2026 04:20:41 +0300

Hi!

> Rebased patches over fresh master.

Thank you for your work on this subject.
I have revised the patchset.  I think it would be better if common
infrastructure goes first.  Otherwise we commit async merge append and
immediately revise it.  I also did some minor improvements.

------
Regards,
Alexander Korotkov
Supabase

---

From: Alexander Korotkov <[email-masked]>
Date: Sun, 5 Apr 2026 05:24:48 +0300

Hi!

On Mon, Mar 30, 2026 at 3:25 PM Matheus Alcantara
<[email-masked]> wrote:
> On 29/03/26 22:20, Alexander Korotkov wrote:
> I was thinking about this but did not managed to spent time on it.
> Thanks for re-organizing the patches, it looks better and I think that
> it make more sense on this order.
>
> I also agree with the minor improvements.

I made more work on the patchset.

Patch #1 now considers IncrementalSort as exclusion alongside with
Sort.  Exclusion check is now on the top of the switch().
Patch #2 is split into 3 patches: common structures, common sync
append logic, and common async append logic.
New structs are now named AppendBase/AppendBaseState, corresponding
fields are "ab" and "as".

Most importantly I noted that this patchset actually only makes
initial heap filling asynchronous.  The steady work after that is
still syncnronous.  Even that it used async infrastructure, it fetched
tuples from children subplans one-by-one: effectively synchronous but
paying for asynchronous infrastructure.  I think even with this
limitation, this patchset is valuable: the startup cost for children
foreignscans can be high.  But this understanding allowed me to
significantly simplify the main patch including:
1) After initial heap filling, use ExecProcNode() to fetch from children plans.
2) Remove ms_has_asyncresults entirely. Async responses store directly
into ms_slots[] (the existing heap slot array), which serves as both
the merge state and the "result arrived" indicator via TupIsNull().
3) Removed needrequest usage from MergeAppend. Since MergeAppend only
fires initial requests (via ExecAppendBaseAsyncBegin()) and never
sends follow-up requests, needrequest tracking is unnecessary.
ExecMergeAppendAsyncRequest() was eliminated entirely.
4)  ExecMergeAppendAsyncGetNext() reduced to a simple wait loop:
5)  asyncresults allocation reduced back to nasyncplans.  MergeAppend
doesn't use it (stores in ms_slots), and Append only needs nasyncplans
entries for its stack.

Additionally, I made the following changes.
1) WAIT_EVENT_MERGE_APPEND_READY wait event instead of extending
WAIT_EVENT_APPEND_READY.  That should be less confusing for monitoring
purposes.
2) More tests: error handling with broken partition, plan-time
partition pruning, and run-time partition pruning tests for async
MergeAppend.

I'm going to went through this patchset another time tomorrow and push
it on Monday if there are no objections.

------
Regards,
Alexander Korotkov
Supabase

---

From: Richard Guo <[email-masked]>
Date: Mon, 6 Apr 2026 12:40:25 +0900

> it on Monday if there are no objections.

I completely understand the desire to get this committed ahead of the
feature freeze.  However, I'm concerned that a one-day notice over the
Easter weekend is simply too short for the community to see the
announcement, let alone provide feedback, especially since this is a
pretty big feature.

I don't have any specific technical feedback on the patchset itself,
as I haven't reviewed it.  My only hesitation is the short notice
period.  That said, if you are highly confident in its readiness, I
will defer to your judgment.

- Richard

---

From: Etsuro Fujita <[email-masked]>
Date: Mon, 6 Apr 2026 14:32:55 +0900

> will defer to your judgment.

First, my apologies for not having reviewed this patch.  I was
planning to do so, but didn't have time for that, due to other
priorities.

I hate to say this, but as mentioned by Richard, this is a pretty big,
complex feature, so I also think the one-day notice is too short.

Best regards,
Etsuro Fujita

---

From: "Matheus Alcantara" <[email-masked]>
Date: Mon, 06 Apr 2026 20:48:05 -0300

> partition pruning, and run-time partition pruning tests for async

Thanks for v17, the split of 0002 into multiple patches seems much
better. Overall I agree with the changes on v17 compared with v16, the
removal of ms_has_asyncresults makes the code better to read and follow.
The separate WAIT_EVENT_MERGE_APPEND_READY for better monitoring is also
good, I've tested some long running queries and I've find the event on
pg_stat_activity. The steady work changes also looks good.

One minor issue on 0002:

+	bool		valid_subplans_identified;	/* is valid_asyncplans valid? */
+	Bitmapset  *valid_subplans;
+	Bitmapset  *valid_asyncplans;	/* valid asynchronous plans indexes */

Should be /* is valid_subplans valid? */

-----

Minor comment on 0005:

+static void
+ExecMergeAppendAsyncGetNext(MergeAppendState *node, int mplan)
+{
+	/*
+	 * All initial async requests were fired by ExecAppendBaseAsyncBegin.

Wondering if we should reference ExecMergeAppendAsyncBegin() instead of
ExecAppendBaseAsyncBegin() since this is on nodeMergeAppend, what do you
think?

---

From: Alexander Korotkov <[email-masked]>
Date: Tue, 7 Apr 2026 03:19:56 +0300

Hi Matheus,

Thank you for your feedback.

> Should be /* is valid_subplans valid? */

Thank you for catching this, fixed.

> ExecAppendBaseAsyncBegin() since this is on nodeMergeAppend, what do you

Technically current comment is correct, because async requests are
essetially fired by ExecAppendBaseAsyncBegin().  But yes, since we're
on nodeMergeAppend, it would be less confusing to mention
ExecMergeAppendAsyncBegin().  Fixed.

------
Regards,
Alexander Korotkov
Supabase

---

From: Alexander Korotkov <[email-masked]>
Date: Tue, 7 Apr 2026 03:25:04 +0300

Hi Richard,
Hi Etsuro,

> complex feature, so I also think the one-day notice is too short.

Thank you for your feedback.  I would say that this patch is here for
quite long, and it's pretty straightforward.  It passed many rounds of
review by Matheus Alcantara.  I've done a lot of minor cleanups and
improvements, and reorganized changes into multiple patches.  The only
major change I did is actually a simplification which come from the
fact that only initial heap filling is effectively async [1].  Today
Matheus gave a feedback on my changes.

Surely, I wouldn't commit this patch without giving you a chance to
review.  We can postpone it till early PG20 development cycle.  But if
you find it possible to take a look at this patch during Apr 7, let me
know.

Links.
1. https://www.postgresql.org/message-id/CAPpHfdsO8zYpDW%3D%3DD6T5N0cJ%2BAzK7a_OyXJoYU1kFi%3DxZFTLuQ%40mail.gmail.com
2. https://www.postgresql.org/message-id/DHMH23M7UOFS.12W6PUDI1I3NH%40gmail.com

------
Regards,
Alexander Korotkov
Supabase

---

From: Etsuro Fujita <[email-masked]>
Date: Tue, 7 Apr 2026 19:25:41 +0900

> Matheus gave a feedback on my changes.

I think Matheus did a good job, but he said "I still don't have too
much experience with the executor code but I hope that I can help with
something.", and IIUC, his reviews were mostly about code
cleanup/deduplication, so ISTM that the patch hadn't been reviewed
that extensively, despite its complexity.  That was actually one of
the reasons why I lowered the priority of the patch.

> you find it possible to take a look at this patch during Apr 7, let me

Sorry, I don't have time for that.  I will defer to your judgment, too.

Thank all of you for working on this important feature, anyway!

Best regards,
Etsuro Fujita

---

From: "Matheus Alcantara" <[email-masked]>
Date: Tue, 07 Apr 2026 10:52:14 -0300

> ExecMergeAppendAsyncBegin().  Fixed.

Thanks for the updated version.

I did another round of review and testing and it looks good to me, I did
not find any issue or strange behaviour.

With the refactor the async support for MergeAppend is not too
complicated. My main concern on this patch series is about the refactor
itself, if we are missing something or changing some behaviour without
notice, however as the  async/sync Append execution is also using the
refactored code and we have a good code coveraged I fell a bit confident
that we are right here.

---

From: Alexander Pyhalov <[email-masked]>
Date: Mon, 13 Apr 2026 18:09:06 +0300

Hi.

Looked at it. Overall I agree that when we wait for data from one slot 
after node initialization, we can't get data from other slots - they are 
already either exhausted, or have already received data which is not 
needed for now. So it seems that async machinery on later stages is 
useless.

Was a bit surprised that asyncresults field is not used in async merge 
append anymore, as we save result directly in ms_slots. However, as we 
do it only on initial stage, this seems to be OK.

classify_matching_subplans() comment still refers to ms_valid_subplans.

Will look at it once again tomorrow.
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional

---

From: Alexander Pyhalov <[email-masked]>
Date: Tue, 14 Apr 2026 12:48:45 +0300

Alexander Pyhalov писал(а) 2026-04-13 18:09:
> after node initialization, we can't get data from other slots - they 
> are already either exhausted, or have already received data which is 
> not needed for now. So it seems that async machinery on later stages is 
> useless.
> 

Haven't found anything suspicious (besides redundant empty line after 
enable_async_merge_append GUC description in 
src/backend/utils/misc/guc_parameters.dat). Tested it and was a bit 
surprised that new async Merge Append version (without async machinery 
after nodeMergeAppend initialization) was about 5% faster than the old 
one with concurrent queries (-j 16) and 10-15% faster with single-thread 
load (when there was a lot of CPU capacity)  in my tests (test was 
basically the same as in [1]). So, async machinery after Merge Append 
node is initialized was not only useless, but even harmful.

Test results:

patch version  | concurrency  | async_capable off | async_capable on
old            |  -c 1 -j 1   | 880  tps          | 1428 tps  (+62%)
old            |  -c 16 -j 16 | 5190 tps          | 4933 tps  (-5%)
new            |  -c 1 -j 1   | 888  tps          | 1582 tps  (+78%)
new            |  -c 16 -j 16 | 5020 tps          | 5256 tps  (+4%)

1. 
https://www.postgresql.org/message-id/159b591411bb2c81332018927acbd509%40postgrespro.ru
-- 
Best regards,
Alexander Pyhalov,
Postgres Professional