postgresql-dropdb--force.20181218_01.patch

diff --git a/doc/src/sgml/ref/drop_database.sgml b/doc/src/sgml/ref/drop_database.sgml
index 3ac06c984a..797763c28f 100644
--- a/doc/src/sgml/ref/drop_database.sgml
+++ b/doc/src/sgml/ref/drop_database.sgml
@@ -79,7 +79,8 @@ DROP DATABASE [ IF EXISTS ] <replaceable class="parameter">name</replaceable>
    This command cannot be executed while connected to the target
    database. Thus, it might be more convenient to use the program
    <xref linkend="app-dropdb"/> instead,
-   which is a wrapper around this command.
+   which is a wrapper around this command, and is also able
+   to terminate existing connections.
   </para>
  </refsect1>
 
diff --git a/doc/src/sgml/ref/dropdb.sgml b/doc/src/sgml/ref/dropdb.sgml
index 38f38f01ce..29fb098e19 100644
--- a/doc/src/sgml/ref/dropdb.sgml
+++ b/doc/src/sgml/ref/dropdb.sgml
@@ -42,8 +42,9 @@ PostgreSQL documentation
   <para>
    <application>dropdb</application> is a wrapper around the
    <acronym>SQL</acronym> command <xref linkend="sql-dropdatabase"/>.
-   There is no effective difference between dropping databases via
-   this utility and via other methods for accessing the server.
+   Other than the <option>--force</option> option, there is no effective
+   difference between dropping databases via this utility and via other
+   methods for accessing the server.
   </para>
 
  </refsect1>
@@ -86,6 +87,22 @@ PostgreSQL documentation
       </listitem>
      </varlistentry>
 
+     <varlistentry>
+      <term><option>-f</option></term>
+      <term><option>--force</option></term>
+      <listitem>
+       <para>
+       Force termination of connected backends before removing the database.
+       </para>
+	   <para>
+	   This will update the <literal>datallowconn</literal> attribute to
+	   disallow incoming connections to target database, send
+	   <literal>SIGTERM</literal> to target backends, and sleep some time
+	   to allow the sessions to terminate.
+	   </para>
+      </listitem>
+     </varlistentry>
+
      <varlistentry>
        <term><option>-V</option></term>
        <term><option>--version</option></term>
diff --git a/src/bin/scripts/dropdb.c b/src/bin/scripts/dropdb.c
index ba0038891d..4bfd8a9397 100644
--- a/src/bin/scripts/dropdb.c
+++ b/src/bin/scripts/dropdb.c
@@ -15,6 +15,10 @@
 #include "fe_utils/string_utils.h"
 
 
+/* Time to sleep after isuing SIGTERM to backends */
+#define TERMINATE_SLEEP_TIME 1
+
+
 static void help(const char *progname);
 
 
@@ -33,6 +37,7 @@ main(int argc, char *argv[])
 		{"interactive", no_argument, NULL, 'i'},
 		{"if-exists", no_argument, &if_exists, 1},
 		{"maintenance-db", required_argument, NULL, 2},
+		{"force", no_argument, NULL, 'f'},
 		{NULL, 0, NULL, 0}
 	};
 
@@ -48,6 +53,7 @@ main(int argc, char *argv[])
 	enum trivalue prompt_password = TRI_DEFAULT;
 	bool		echo = false;
 	bool		interactive = false;
+	bool		force = false;
 
 	PQExpBufferData sql;
 
@@ -59,7 +65,7 @@ main(int argc, char *argv[])
 
 	handle_help_version_opts(argc, argv, "dropdb", help);
 
-	while ((c = getopt_long(argc, argv, "h:p:U:wWei", long_options, &optindex)) != -1)
+	while ((c = getopt_long(argc, argv, "h:p:U:wWeif", long_options, &optindex)) != -1)
 	{
 		switch (c)
 		{
@@ -84,6 +90,9 @@ main(int argc, char *argv[])
 			case 'i':
 				interactive = true;
 				break;
+			case 'f':
+				force = true;
+				break;
 			case 0:
 				/* this covers the long options */
 				break;
@@ -121,9 +130,6 @@ main(int argc, char *argv[])
 
 	initPQExpBuffer(&sql);
 
-	appendPQExpBuffer(&sql, "DROP DATABASE %s%s;",
-					  (if_exists ? "IF EXISTS " : ""), fmtId(dbname));
-
 	/* Avoid trying to drop postgres db while we are connected to it. */
 	if (maintenance_db == NULL && strcmp(dbname, "postgres") == 0)
 		maintenance_db = "template1";
@@ -132,6 +138,64 @@ main(int argc, char *argv[])
 									  host, port, username, prompt_password,
 									  progname, echo);
 
+	if (force)
+	{
+		/* TODO: revert this UPDATE in case removal fails for any reason */
+		appendPQExpBufferStr(&sql,
+							 "UPDATE pg_catalog.pg_database\n"
+							 " SET datallowconn = 'false'\n"
+							 " WHERE datname OPERATOR(pg_catalog.=) ");
+		appendStringLiteralConn(&sql, dbname, conn);
+		appendPQExpBufferStr(&sql, ";\n");
+		if (echo)
+			printf("%s\n", sql.data);
+		result = PQexec(conn, sql.data);
+		if (PQresultStatus(result) != PGRES_COMMAND_OK)
+		{
+			fprintf(stderr, _("%s: database removal failed: %s"),
+					progname, PQerrorMessage(conn));
+			PQfinish(conn);
+			exit(1);
+		}
+
+		PQclear(result);
+
+		resetPQExpBuffer(&sql);
+
+		appendPQExpBufferStr(&sql,
+							"SELECT pg_catalog.pg_terminate_backend(pid)\n"
+							" FROM pg_catalog.pg_stat_activity\n"
+							" WHERE pid OPERATOR(pg_catalog.<>) pg_catalog.pg_backend_pid()\n"
+							" AND datname OPERATOR(pg_catalog.=) ");
+		appendStringLiteralConn(&sql, dbname, conn);
+		appendPQExpBufferStr(&sql, ";\n");
+
+		if (echo)
+			printf("%s\n", sql.data);
+		result = PQexec(conn, sql.data);
+		if (PQresultStatus(result) == PGRES_TUPLES_OK)
+		{
+			if (PQntuples(result) > 0)
+				printf("%s: sent SIGTERM to %d backend(s)\n",
+					   progname, PQntuples(result));
+				pg_usleep(TERMINATE_SLEEP_TIME * 1000000);
+		}
+		else
+		{
+			fprintf(stderr, _("%s: database removal failed: %s"),
+					progname, PQerrorMessage(conn));
+			PQfinish(conn);
+			exit(1);
+		}
+
+		PQclear(result);
+
+		resetPQExpBuffer(&sql);
+	}
+
+	appendPQExpBuffer(&sql, "DROP DATABASE %s%s;",
+					  (if_exists ? "IF EXISTS " : ""), fmtId(dbname));
+
 	if (echo)
 		printf("%s\n", sql.data);
 	result = PQexec(conn, sql.data);
@@ -158,6 +222,7 @@ help(const char *progname)
 	printf(_("\nOptions:\n"));
 	printf(_("  -e, --echo                show the commands being sent to the server\n"));
 	printf(_("  -i, --interactive         prompt before deleting anything\n"));
+	printf(_("  -f, --force               force termination of connected backends\n"));
 	printf(_("  -V, --version             output version information, then exit\n"));
 	printf(_("  --if-exists               don't report error if database doesn't exist\n"));
 	printf(_("  -?, --help                show this help, then exit\n"));
diff --git a/src/bin/scripts/t/050_dropdb.pl b/src/bin/scripts/t/050_dropdb.pl
index 25aa54a4ae..24663255ec 100644
--- a/src/bin/scripts/t/050_dropdb.pl
+++ b/src/bin/scripts/t/050_dropdb.pl
@@ -19,5 +19,11 @@ $node->issues_sql_like(
 	qr/statement: DROP DATABASE foobar1/,
 	'SQL DROP DATABASE run');
 
+$node->safe_psql('postgres', 'CREATE DATABASE foobar2');
+$node->issues_sql_like(
+	[ 'dropdb', '--force', 'foobar2' ],
+	qr/statement: SELECT pg_catalog[.]pg_terminate_backend[(]pid[)]/,
+	'SQL pg_terminate_backend run');
+
 $node->command_fails([ 'dropdb', 'nonexistent' ],
 	'fails with nonexistent database');