Add reconnect option to control automatic reconnection to MySQL server.

The MySQL client library can perform an automatic reconnection to the
server if it finds the connection is down when one attempts to send
a statement to the server to be executed, and it is controlled by
MySQL option MYSQL_OPT_RECONNECT. This allows a seamless operation in
case the connection got dropped intermittently. Add a mysql_fdw
server-level option 'reconnect' to control this behavior for
mysql_fdw internal connections.

Reported on GitHub through issue #215 by Magmatrix.

FDW-350, Suraj Kharage, reviewed by Jeevan Ladhe.

Author: jeevanladhe

README.md

@@ -115,6 +115,9 @@ The following parameters can be set on a MySQL foreign server object:
     MySQL server.
   * `use_remote_estimate`: Controls whether mysql_fdw issues remote
     EXPLAIN commands to obtain cost estimates. Default is `false`
+  * `reconnect`: Enable or disable automatic reconnection to the
+    MySQL server if the existing connection is found to have been lost.
+    Default is `false`.
   * `ssl_key`: The path name of the client private key file.
   * `ssl_cert`: The path name of the client public key certificate file.
   * `ssl_ca`: The path name of the Certificate Authority (CA) certificate

connection.c

@@ -244,6 +244,12 @@ mysql_connect(mysql_opt *opt)
 	if (svr_init_command != NULL)
 		mysql_options(conn, MYSQL_INIT_COMMAND, svr_init_command);
 
+	/*
+	 * Enable or disable automatic reconnection to the MySQL server if
+	 * the existing connection is found to have been lost.
+	 */
+	mysql_options(conn, MYSQL_OPT_RECONNECT, &opt->reconnect);
+
 	mysql_ssl_set(conn, opt->ssl_key, opt->ssl_cert, opt->ssl_ca,
 				   opt->ssl_capath, ssl_cipher);
 

expected/server_options.out

@@ -243,5 +243,32 @@ ERROR:  "fetch_size" requires an integer value between 1 to 18446744073709551615
 -- Cleanup fetch_size test objects.
 DROP FOREIGN TABLE  table30000;
 DROP SERVER fetch101;
+-- FDW-350: Support for reconnect option at server level.
+CREATE SERVER reconnect1 FOREIGN DATA WRAPPER mysql_fdw
+  OPTIONS( reconnect 'true' );
+SELECT count(*)
+  FROM pg_foreign_server
+  WHERE srvname = 'reconnect1'
+  AND srvoptions @> array['reconnect=true'];
+ count 
+-------
+     1
+(1 row)
+
+ALTER SERVER reconnect1 OPTIONS( SET reconnect 'false' );
+SELECT count(*)
+  FROM pg_foreign_server
+  WHERE srvname = 'reconnect1'
+  AND srvoptions @> array['reconnect=false'];
+ count 
+-------
+     1
+(1 row)
+
+-- Negative test case for reconnect option, should error out.
+ALTER SERVER reconnect1 OPTIONS ( SET reconnect 'abc1' );
+ERROR:  reconnect requires a Boolean value
+-- Cleanup reconnect option test objects.
+DROP SERVER reconnect1;
 -- Cleanup
 DROP EXTENSION mysql_fdw;

mysql_fdw.h

@@ -102,6 +102,7 @@ typedef struct mysql_opt
 									 * truncation */
 	bool		use_remote_estimate;	/* use remote estimate for rows */
 	unsigned long fetch_size;	/* Number of rows to fetch from remote server */
+	bool		reconnect;		/* set to true for automatic reconnection */
 
 	/* SSL parameters; unused options may be given as NULL */
 	char	   *ssl_key;		/* MySQL SSL: path to the key file */

option.c

@@ -51,6 +51,7 @@ static struct MySQLFdwOption valid_options[] =
 	/* fetch_size is available on both server and table */
 	{"fetch_size", ForeignServerRelationId},
 	{"fetch_size", ForeignTableRelationId},
+	{"reconnect", ForeignServerRelationId},
 	{"ssl_key", ForeignServerRelationId},
 	{"ssl_cert", ForeignServerRelationId},
 	{"ssl_ca", ForeignServerRelationId},
@@ -137,6 +138,11 @@ mysql_fdw_validator(PG_FUNCTION_ARGS)
 						 errmsg("\"%s\" requires an integer value between 1 to %lu",
 								def->defname, ULONG_MAX)));
 		}
+		else if (strcmp(def->defname, "reconnect") == 0)
+		{
+			/* accept only boolean values */
+			(void) defGetBoolean(def);
+		}
 	}
 
 	PG_RETURN_VOID();
@@ -203,6 +209,7 @@ mysql_get_options(Oid foreignoid, bool is_foreigntable)
 	opt->svr_sa = true;
 
 	opt->use_remote_estimate = false;
+	opt->reconnect = false;
 
 	/* Loop through the options */
 	foreach(lc, options)
@@ -242,6 +249,9 @@ mysql_get_options(Oid foreignoid, bool is_foreigntable)
 		if (strcmp(def->defname, "fetch_size") == 0)
 			opt->fetch_size = strtoul(defGetString(def), NULL, 10);
 
+		if (strcmp(def->defname, "reconnect") == 0)
+			opt->reconnect = defGetBoolean(def);
+
 		if (strcmp(def->defname, "ssl_key") == 0)
 			opt->ssl_key = defGetString(def);
 

sql/server_options.sql

@@ -172,5 +172,27 @@ ALTER FOREIGN TABLE table30000 OPTIONS ( SET fetch_size '999999999999999999999')
 DROP FOREIGN TABLE  table30000;
 DROP SERVER fetch101;
 
+-- FDW-350: Support for reconnect option at server level.
+CREATE SERVER reconnect1 FOREIGN DATA WRAPPER mysql_fdw
+  OPTIONS( reconnect 'true' );
+
+SELECT count(*)
+  FROM pg_foreign_server
+  WHERE srvname = 'reconnect1'
+  AND srvoptions @> array['reconnect=true'];
+
+ALTER SERVER reconnect1 OPTIONS( SET reconnect 'false' );
+
+SELECT count(*)
+  FROM pg_foreign_server
+  WHERE srvname = 'reconnect1'
+  AND srvoptions @> array['reconnect=false'];
+
+-- Negative test case for reconnect option, should error out.
+ALTER SERVER reconnect1 OPTIONS ( SET reconnect 'abc1' );
+
+-- Cleanup reconnect option test objects.
+DROP SERVER reconnect1;
+
 -- Cleanup
 DROP EXTENSION mysql_fdw;