Implement support for bulk inserts in postgres_fdw

Extends the FDW API to allow batching inserts into foreign tables. That
is usually much more efficient than inserting individual rows, due to
high latency for each round-trip to the foreign server.

It was possible to implement something similar in the regular FDW API,
but it was inconvenient and there were issues with reporting the number
of actually inserted rows etc. This extends the FDW API with two new
functions:

* GetForeignModifyBatchSize - allows the FDW picking optimal batch size

* ExecForeignBatchInsert - inserts a batch of rows at once

Currently, only INSERT queries support batching. Support for DELETE and
UPDATE may be added in the future.

This also implements batching for postgres_fdw. The batch size may be
specified using "batch_size" option both at the server and table level.

The initial patch version was written by me, but it was rewritten and
improved in many ways by Takayuki Tsunakawa.

Author: Takayuki Tsunakawa
Reviewed-by: Tomas Vondra, Amit Langote
Discussion: https://postgr.es/m/20200628151002.7x5laxwpgvkyiu3q@development

1 files changed, 93 insertions, 0 deletions

diff --git a/contrib/postgres_fdw/sql/postgres_fdw.sql b/contrib/postgres_fdw/sql/postgres_fdw.sql
index ebf6eb10a61..28b82f5f9dc 100644
--- a/contrib/postgres_fdw/sql/postgres_fdw.sql
+++ b/contrib/postgres_fdw/sql/postgres_fdw.sql
@@ -2738,3 +2738,96 @@ COMMIT;
 -- should not be output because they should be closed at the end of
 -- the above transaction.
 SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
+
+-- ===================================================================
+-- batch insert
+-- ===================================================================
+
+BEGIN;
+
+CREATE SERVER batch10 FOREIGN DATA WRAPPER postgres_fdw OPTIONS( batch_size '10' );
+
+SELECT count(*)
+FROM pg_foreign_server
+WHERE srvname = 'batch10'
+AND srvoptions @> array['batch_size=10'];
+
+ALTER SERVER batch10 OPTIONS( SET batch_size '20' );
+
+SELECT count(*)
+FROM pg_foreign_server
+WHERE srvname = 'batch10'
+AND srvoptions @> array['batch_size=10'];
+
+SELECT count(*)
+FROM pg_foreign_server
+WHERE srvname = 'batch10'
+AND srvoptions @> array['batch_size=20'];
+
+CREATE FOREIGN TABLE table30 ( x int ) SERVER batch10 OPTIONS ( batch_size '30' );
+
+SELECT COUNT(*)
+FROM pg_foreign_table
+WHERE ftrelid = 'table30'::regclass
+AND ftoptions @> array['batch_size=30'];
+
+ALTER FOREIGN TABLE table30 OPTIONS ( SET batch_size '40');
+
+SELECT COUNT(*)
+FROM pg_foreign_table
+WHERE ftrelid = 'table30'::regclass
+AND ftoptions @> array['batch_size=30'];
+
+SELECT COUNT(*)
+FROM pg_foreign_table
+WHERE ftrelid = 'table30'::regclass
+AND ftoptions @> array['batch_size=40'];
+
+ROLLBACK;
+
+CREATE TABLE batch_table ( x int );
+
+CREATE FOREIGN TABLE ftable ( x int ) SERVER loopback OPTIONS ( table_name 'batch_table', batch_size '10' );
+EXPLAIN (VERBOSE, COSTS OFF) INSERT INTO ftable SELECT * FROM generate_series(1, 10) i;
+INSERT INTO ftable SELECT * FROM generate_series(1, 10) i;
+INSERT INTO ftable SELECT * FROM generate_series(11, 31) i;
+INSERT INTO ftable VALUES (32);
+INSERT INTO ftable VALUES (33), (34);
+SELECT COUNT(*) FROM ftable;
+TRUNCATE batch_table;
+DROP FOREIGN TABLE ftable;
+
+-- Disable batch insert
+CREATE FOREIGN TABLE ftable ( x int ) SERVER loopback OPTIONS ( table_name 'batch_table', batch_size '1' );
+EXPLAIN (VERBOSE, COSTS OFF) INSERT INTO ftable VALUES (1), (2);
+INSERT INTO ftable VALUES (1), (2);
+SELECT COUNT(*) FROM ftable;
+DROP FOREIGN TABLE ftable;
+DROP TABLE batch_table;
+
+-- Use partitioning
+CREATE TABLE batch_table ( x int ) PARTITION BY HASH (x);
+
+CREATE TABLE batch_table_p0 (LIKE batch_table);
+CREATE FOREIGN TABLE batch_table_p0f
+	PARTITION OF batch_table
+	FOR VALUES WITH (MODULUS 3, REMAINDER 0)
+	SERVER loopback
+	OPTIONS (table_name 'batch_table_p0', batch_size '10');
+
+CREATE TABLE batch_table_p1 (LIKE batch_table);
+CREATE FOREIGN TABLE batch_table_p1f
+	PARTITION OF batch_table
+	FOR VALUES WITH (MODULUS 3, REMAINDER 1)
+	SERVER loopback
+	OPTIONS (table_name 'batch_table_p1', batch_size '1');
+
+CREATE TABLE batch_table_p2
+	PARTITION OF batch_table
+	FOR VALUES WITH (MODULUS 3, REMAINDER 2);
+
+INSERT INTO batch_table SELECT * FROM generate_series(1, 66) i;
+SELECT COUNT(*) FROM batch_table;
+
+-- Clean up
+DROP TABLE batch_table CASCADE;