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

Author: tvondra

contrib/postgres_fdw/deparse.c

@@ -1705,13 +1705,16 @@ deparseRangeTblRef(StringInfo buf, PlannerInfo *root, RelOptInfo *foreignrel,
  * The statement text is appended to buf, and we also create an integer List
  * of the columns being retrieved by WITH CHECK OPTION or RETURNING (if any),
  * which is returned to *retrieved_attrs.
+ *
+ * This also stores end position of the VALUES clause, so that we can rebuild
+ * an INSERT for a batch of rows later.
  */
 void
 deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
 				 Index rtindex, Relation rel,
 				 List *targetAttrs, bool doNothing,
 				 List *withCheckOptionList, List *returningList,
-				 List **retrieved_attrs)
+				 List **retrieved_attrs, int *values_end_len)
 {
 	AttrNumber	pindex;
 	bool		first;
@@ -1754,6 +1757,7 @@ deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
 	}
 	else
 		appendStringInfoString(buf, " DEFAULT VALUES");
+	*values_end_len = buf->len;
 
 	if (doNothing)
 		appendStringInfoString(buf, " ON CONFLICT DO NOTHING");
@@ -1763,6 +1767,54 @@ deparseInsertSql(StringInfo buf, RangeTblEntry *rte,
 						 withCheckOptionList, returningList, retrieved_attrs);
 }
 
+/*
+ * rebuild remote INSERT statement
+ *
+ * Provided a number of rows in a batch, builds INSERT statement with the
+ * right number of parameters.
+ */
+void
+rebuildInsertSql(StringInfo buf, char *orig_query,
+				 int values_end_len, int num_cols,
+				 int num_rows)
+{
+	int			i, j;
+	int			pindex;
+	bool		first;
+
+	/* Make sure the values_end_len is sensible */
+	Assert((values_end_len > 0) && (values_end_len <= strlen(orig_query)));
+
+	/* Copy up to the end of the first record from the original query */
+	appendBinaryStringInfo(buf, orig_query, values_end_len);
+
+	/*
+	 * Add records to VALUES clause (we already have parameters for the
+	 * first row, so start at the right offset).
+	 */
+	pindex = num_cols + 1;
+	for (i = 0; i < num_rows; i++)
+	{
+		appendStringInfoString(buf, ", (");
+
+		first = true;
+		for (j = 0; j < num_cols; j++)
+		{
+			if (!first)
+				appendStringInfoString(buf, ", ");
+			first = false;
+
+			appendStringInfo(buf, "$%d", pindex);
+			pindex++;
+		}
+
+		appendStringInfoChar(buf, ')');
+	}
+
+	/* Copy stuff after VALUES clause from the original query */
+	appendStringInfoString(buf, orig_query + values_end_len);
+}
+
 /*
  * deparse remote UPDATE statement
  *

contrib/postgres_fdw/expected/postgres_fdw.out

@@ -3887,9 +3887,10 @@ EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st7;
 -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Insert on public.ft1
    Remote SQL: INSERT INTO "S 1"."T 1"("C 1", c2, c3, c4, c5, c6, c7, c8) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+   Batch Size: 1
    ->  Result
          Output: NULL::integer, 1001, 101, 'foo'::text, NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying, 'ft1       '::character(10), NULL::user_enum
-(4 rows)
+(5 rows)
 
 ALTER TABLE "S 1"."T 1" RENAME TO "T 0";
 ALTER FOREIGN TABLE ft1 OPTIONS (SET table_name 'T 0');
@@ -3920,9 +3921,10 @@ EXPLAIN (VERBOSE, COSTS OFF) EXECUTE st7;
 -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Insert on public.ft1
    Remote SQL: INSERT INTO "S 1"."T 0"("C 1", c2, c3, c4, c5, c6, c7, c8) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+   Batch Size: 1
    ->  Result
          Output: NULL::integer, 1001, 101, 'foo'::text, NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying, 'ft1       '::character(10), NULL::user_enum
-(4 rows)
+(5 rows)
 
 ALTER TABLE "S 1"."T 0" RENAME TO "T 1";
 ALTER FOREIGN TABLE ft1 OPTIONS (SET table_name 'T 1');
@@ -4244,12 +4246,13 @@ INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Insert on public.ft2
    Remote SQL: INSERT INTO "S 1"."T 1"("C 1", c2, c3, c4, c5, c6, c7, c8) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+   Batch Size: 1
    ->  Subquery Scan on "*SELECT*"
          Output: "*SELECT*"."?column?", "*SELECT*"."?column?_1", NULL::integer, "*SELECT*"."?column?_2", NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying, 'ft2       '::character(10), NULL::user_enum
          ->  Foreign Scan on public.ft2 ft2_1
                Output: (ft2_1.c1 + 1000), (ft2_1.c2 + 100), (ft2_1.c3 || ft2_1.c3)
                Remote SQL: SELECT "C 1", c2, c3 FROM "S 1"."T 1" LIMIT 20::bigint
-(7 rows)
+(8 rows)
 
 INSERT INTO ft2 (c1,c2,c3) SELECT c1+1000,c2+100, c3 || c3 FROM ft2 LIMIT 20;
 INSERT INTO ft2 (c1,c2,c3)
@@ -5360,9 +5363,10 @@ INSERT INTO ft2 (c1,c2,c3) VALUES (1200,999,'foo') RETURNING tableoid::regclass;
  Insert on public.ft2
    Output: (ft2.tableoid)::regclass
    Remote SQL: INSERT INTO "S 1"."T 1"("C 1", c2, c3, c4, c5, c6, c7, c8) VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
+   Batch Size: 1
    ->  Result
          Output: 1200, 999, NULL::integer, 'foo'::text, NULL::timestamp with time zone, NULL::timestamp without time zone, NULL::character varying, 'ft2       '::character(10), NULL::user_enum
-(5 rows)
+(6 rows)
 
 INSERT INTO ft2 (c1,c2,c3) VALUES (1200,999,'foo') RETURNING tableoid::regclass;
  tableoid 
@@ -6212,9 +6216,10 @@ INSERT INTO rw_view VALUES (0, 5);
 --------------------------------------------------------------------------------
  Insert on public.foreign_tbl
    Remote SQL: INSERT INTO public.base_tbl(a, b) VALUES ($1, $2) RETURNING a, b
+   Batch Size: 1
    ->  Result
          Output: 0, 5
-(4 rows)
+(5 rows)
 
 INSERT INTO rw_view VALUES (0, 5); -- should fail
 ERROR:  new row violates check option for view "rw_view"
@@ -6225,9 +6230,10 @@ INSERT INTO rw_view VALUES (0, 15);
 --------------------------------------------------------------------------------
  Insert on public.foreign_tbl
    Remote SQL: INSERT INTO public.base_tbl(a, b) VALUES ($1, $2) RETURNING a, b
+   Batch Size: 1
    ->  Result
          Output: 0, 15
-(4 rows)
+(5 rows)
 
 INSERT INTO rw_view VALUES (0, 15); -- ok
 SELECT * FROM foreign_tbl;
@@ -8923,7 +8929,7 @@ DO $d$
     END;
 $d$;
 ERROR:  invalid option "password"
-HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size
+HINT:  Valid options in this context are: service, passfile, channel_binding, connect_timeout, dbname, host, hostaddr, port, options, application_name, keepalives, keepalives_idle, keepalives_interval, keepalives_count, tcp_user_timeout, sslmode, sslcompression, sslcert, sslkey, sslrootcert, sslcrl, requirepeer, ssl_min_protocol_version, ssl_max_protocol_version, gssencmode, krbsrvname, gsslib, target_session_attrs, use_remote_estimate, fdw_startup_cost, fdw_tuple_cost, extensions, updatable, fetch_size, batch_size
 CONTEXT:  SQL statement "ALTER SERVER loopback_nopw OPTIONS (ADD password 'dummypw')"
 PL/pgSQL function inline_code_block line 3 at EXECUTE
 -- If we add a password for our user mapping instead, we should get a different
@@ -9112,3 +9118,138 @@ SELECT * FROM postgres_fdw_get_connections() ORDER BY 1;
  loopback2   | t
 (1 row)
 
+-- ===================================================================
+-- 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'];
+ count 
+-------
+     1
+(1 row)
+
+ALTER SERVER batch10 OPTIONS( SET batch_size '20' );
+SELECT count(*)
+FROM pg_foreign_server
+WHERE srvname = 'batch10'
+AND srvoptions @> array['batch_size=10'];
+ count 
+-------
+     0
+(1 row)
+
+SELECT count(*)
+FROM pg_foreign_server
+WHERE srvname = 'batch10'
+AND srvoptions @> array['batch_size=20'];
+ count 
+-------
+     1
+(1 row)
+
+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'];
+ count 
+-------
+     1
+(1 row)
+
+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'];
+ count 
+-------
+     0
+(1 row)
+
+SELECT COUNT(*)
+FROM pg_foreign_table
+WHERE ftrelid = 'table30'::regclass
+AND ftoptions @> array['batch_size=40'];
+ count 
+-------
+     1
+(1 row)
+
+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;
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Insert on public.ftable
+   Remote SQL: INSERT INTO public.batch_table(x) VALUES ($1)
+   Batch Size: 10
+   ->  Function Scan on pg_catalog.generate_series i
+         Output: i.i
+         Function Call: generate_series(1, 10)
+(6 rows)
+
+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;
+ count 
+-------
+    34
+(1 row)
+
+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);
+                         QUERY PLAN                          
+-------------------------------------------------------------
+ Insert on public.ftable
+   Remote SQL: INSERT INTO public.batch_table(x) VALUES ($1)
+   Batch Size: 1
+   ->  Values Scan on "*VALUES*"
+         Output: "*VALUES*".column1
+(5 rows)
+
+INSERT INTO ftable VALUES (1), (2);
+SELECT COUNT(*) FROM ftable;
+ count 
+-------
+     2
+(1 row)
+
+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;
+ count 
+-------
+    66
+(1 row)
+
+-- Clean up
+DROP TABLE batch_table CASCADE;

contrib/postgres_fdw/option.c

@@ -142,6 +142,17 @@ postgres_fdw_validator(PG_FUNCTION_ARGS)
 						 errmsg("%s requires a non-negative integer value",
 								def->defname)));
 		}
+		else if (strcmp(def->defname, "batch_size") == 0)
+		{
+			int			batch_size;
+
+			batch_size = strtol(defGetString(def), NULL, 10);
+			if (batch_size <= 0)
+				ereport(ERROR,
+						(errcode(ERRCODE_SYNTAX_ERROR),
+						 errmsg("%s requires a non-negative integer value",
+								def->defname)));
+		}
 		else if (strcmp(def->defname, "password_required") == 0)
 		{
 			bool		pw_required = defGetBoolean(def);
@@ -203,6 +214,9 @@ InitPgFdwOptions(void)
 		/* fetch_size is available on both server and table */
 		{"fetch_size", ForeignServerRelationId, false},
 		{"fetch_size", ForeignTableRelationId, false},
+		/* batch_size is available on both server and table */
+		{"batch_size", ForeignServerRelationId, false},
+		{"batch_size", ForeignTableRelationId, false},
 		{"password_required", UserMappingRelationId, false},
 
 		/*