CASSANDRA-21539: Avoid DNS lookup for hostname column in ClientsTable and GossipInfoTable (6.0)

CHANGES.txt

@@ -30,11 +30,11 @@ Merged from 5.0:
  * Fix ThreadLocalReadAheadBuffer#fill() to throw a CorruptBlockException if chunk metadata and file size are out of sync (CASSANDRA-21519)
  * Fix memtable on-heap accounting drift in BTree.update and BTreeRow.merge (CASSANDRA-21472)
 Merged from 4.0:
+ * Avoid DNS lookup for hostname column in ClientsTable and GossipInfoTable (CASSANDRA-21539)
  * During streaming Bounds.getNonOverlappingBounds produces incorrect bounds leading to row/counter cache not invalidate correctly (CASSANDRA-21594)
  * Validate authz before performing role check in LIST ROLES/PERMISSIONS (CASSANDRA-21560)
  * Add validation to uncompressed length during decompression (CASSANDRA-21567)
  * Fix regression in PasswordObfuscator for dollar-quoted passwords (CASSANDRA-21559)
- * Do not make DNS lookup when querying system_views.clients for hostname column by removing it (CASSANDRA-21539)
  * Fix memtable on-heap accounting drift in BTree.update and BTreeRow.merge (CASSANDRA-21472)
  * Include missing cassandra-jaas.config file in Debian package (CASSANDRA-19750)
 

NEWS.txt

@@ -209,6 +209,9 @@ Upgrading
     unchanged, and the datacenter and CIDR checks that ride along with them still run at least once per
     request. Auth cache request/hit/miss counts and the system_views.cidr_filtering_metrics_* counts and
     latencies will therefore report fewer events than before. (see CASSANDRA-21606)
+    - The hostname column in system_views.clients will no longer perform a reverse DNS lookup and will instead
+    return the same value as the address column. This avoids the risk of client connections overwhelming
+    DNS. (CASSANDRA-21539)
 
 Deprecation
 -----------

doc/modules/cassandra/pages/managing/operating/virtualtables.adoc

@@ -175,7 +175,7 @@ We shall discuss some of the virtual tables in more detail next.
 
 The `clients` virtual table lists all active connections (connected
 clients) including their ip address, port, client_options, connection stage, driver
-name, driver version, protocol version, request count, ssl
+name, driver version, hostname, protocol version, request count, ssl
 enabled, ssl protocol and user name:
 
 [source, console]
@@ -190,6 +190,7 @@ cqlsh> SELECT * FROM system_views.clients;
  connection_stage | ready
  driver_name      | DataStax Python Driver
  driver_version   | 3.25.0
+ hostname         | localhost
  protocol_version | 5
  request_count    | 16
  ssl_cipher_suite | null
@@ -205,6 +206,7 @@ cqlsh> SELECT * FROM system_views.clients;
  connection_stage | ready
  driver_name      | DataStax Python Driver
  driver_version   | 3.25.0
+ hostname         | localhost
  protocol_version | 5
  request_count    | 4
  ssl_cipher_suite | null
@@ -220,6 +222,7 @@ cqlsh> SELECT * FROM system_views.clients;
  connection_stage | ready
  driver_name      | DataStax Java driver for Apache Cassandra(R)
  driver_version   | 4.13.0
+ hostname         | localhost
  protocol_version | 5
  request_count    | 18
  ssl_cipher_suite | null
@@ -235,6 +238,7 @@ cqlsh> SELECT * FROM system_views.clients;
  connection_stage | ready
  driver_name      | DataStax Java driver for Apache Cassandra(R)
  driver_version   | 4.13.0
+ hostname         | localhost
  protocol_version | 5
  request_count    | 7
  ssl_cipher_suite | null
@@ -271,6 +275,7 @@ VIRTUAL TABLE system_views.clients (
   connection_stage text,
   driver_name text,
   driver_version text,
+  hostname text,
   protocol_version int,
   request_count bigint,
   ssl_cipher_suite text,
@@ -668,10 +673,10 @@ results in:
 +
 [source, cql]
 ----
- address   | port  | connection_stage | driver_name            | driver_version | protocol_version | request_count | ssl_cipher_suite | ssl_enabled | ssl_protocol | username
------------+-------+------------------+------------------------+----------------+------------------+---------------+------------------+-------------+--------------+-----------
- 127.0.0.1 | 37308 |            ready | DataStax Python Driver |   3.21.0.post0 |                4 |            17 |             null |       False |         null | anonymous
- 127.0.0.1 | 37310 |            ready | DataStax Python Driver |   3.21.0.post0 |                4 |             8 |             null |       False |         null | anonymous
+ address   | port  | connection_stage | driver_name            | driver_version | hostname  | protocol_version | request_count | ssl_cipher_suite | ssl_enabled | ssl_protocol | username
+-----------+-------+------------------+------------------------+----------------+-----------|||+------------------+---------------+------------------+-------------+--------------+-----------
+ 127.0.0.1 | 37308 |            ready | DataStax Python Driver |   3.21.0.post0 | localhost |                4 |            17 |             null |       False |         null | anonymous
+ 127.0.0.1 | 37310 |            ready | DataStax Python Driver |   3.21.0.post0 | localhost |                4 |             8 |             null |       False |         null | anonymous
 
 (2 rows)
 ----

src/java/org/apache/cassandra/db/virtual/ClientsTable.java

@@ -38,6 +38,7 @@ final class ClientsTable extends AbstractVirtualTable
 {
     private static final String ADDRESS = "address";
     private static final String PORT = "port";
+    private static final String HOSTNAME = "hostname";
     private static final String USERNAME = "username";
     private static final String CONNECTION_STAGE = "connection_stage";
     private static final String PROTOCOL_VERSION = "protocol_version";
@@ -60,6 +61,7 @@ final class ClientsTable extends AbstractVirtualTable
                            .partitioner(new LocalPartitioner(InetAddressType.instance))
                            .addPartitionKeyColumn(ADDRESS, InetAddressType.instance)
                            .addClusteringColumn(PORT, Int32Type.instance)
+                           .addRegularColumn(HOSTNAME, UTF8Type.instance)
                            .addRegularColumn(USERNAME, UTF8Type.instance)
                            .addRegularColumn(CONNECTION_STAGE, UTF8Type.instance)
                            .addRegularColumn(PROTOCOL_VERSION, Int32Type.instance)
@@ -86,6 +88,7 @@ public DataSet data()
             InetSocketAddress remoteAddress = client.remoteAddress();
 
             result.row(remoteAddress.getAddress(), remoteAddress.getPort())
+                  .column(HOSTNAME, remoteAddress.getHostString())
                   .column(USERNAME, client.username().orElse(null))
                   .column(CONNECTION_STAGE, toLowerCaseLocalized(client.stage().toString()))
                   .column(PROTOCOL_VERSION, client.protocolVersion())

src/java/org/apache/cassandra/db/virtual/GossipInfoTable.java

@@ -48,6 +48,7 @@ final class GossipInfoTable extends AbstractVirtualTable
 
     static final String ADDRESS = "address";
     static final String PORT = "port";
+    static final String HOSTNAME = "hostname";
     static final String GENERATION = "generation";
     static final String HEARTBEAT = "heartbeat";
 
@@ -97,6 +98,7 @@ public DataSet data()
             EndpointState localState = new EndpointState(entry.getValue());
 
             SimpleDataSet dataSet = result.row(endpoint.getAddress(), endpoint.getPort())
+                                          .column(HOSTNAME, endpoint.getHostString())
                                           .column(GENERATION, getGeneration(localState))
                                           .column(HEARTBEAT, getHeartBeat(localState));
 
@@ -173,6 +175,7 @@ private static TableMetadata buildTableMetadata(String keyspace)
                                                      .partitioner(new LocalPartitioner(InetAddressType.instance))
                                                      .addPartitionKeyColumn(ADDRESS, InetAddressType.instance)
                                                      .addClusteringColumn(PORT, Int32Type.instance)
+                                                     .addRegularColumn(HOSTNAME, UTF8Type.instance)
                                                      .addRegularColumn(GENERATION, Int32Type.instance)
                                                      .addRegularColumn(HEARTBEAT, Int32Type.instance);
 

test/unit/org/apache/cassandra/db/virtual/ClientsTableTest.java

@@ -70,7 +70,7 @@ public void testSelectAll()
         shouldUseEncryption(true);
         shouldUseClientCertificate(true);
         ResultSet result = executeNet("SELECT * FROM vts.clients");
-        assertThat(result.getColumnDefinitions().size()).isEqualTo(15);
+        assertThat(result.getColumnDefinitions().size()).isEqualTo(16);
         for (Row r : result)
         {
             Assert.assertEquals(InetAddress.getLoopbackAddress(), r.getInet("address"));
@@ -79,6 +79,7 @@ public void testSelectAll()
             Assert.assertNotNull(r.getMap("client_options", String.class, String.class));
             Assert.assertTrue(r.getLong("request_count") > 0 );
             // the following are questionable if they belong here
+            Assert.assertEquals(r.getInet("address").getHostAddress(), r.getString("hostname"));
             Assertions.assertThat(r.getMap("client_options", String.class, String.class))
                       .hasEntrySatisfying("DRIVER_VERSION", value -> assertThat(value.contains(r.getString("driver_name"))))
                       .hasEntrySatisfying("DRIVER_VERSION", value -> assertThat(value.contains(r.getString("driver_version"))));

test/unit/org/apache/cassandra/db/virtual/GossipInfoTableTest.java

@@ -70,12 +70,13 @@ public void testSelectAllWithStateTransitions() throws Throwable
 
             assertThat(resultSet.size()).isEqualTo(1);
             UntypedResultSet.Row row = resultSet.one();
-            assertThat(row.getColumns().size()).isEqualTo(65);
+            assertThat(row.getColumns().size()).isEqualTo(66);
 
             assertThat(endpoint).isNotNull();
             assertThat(localState).isNotNull();
             assertThat(row.getInetAddress("address")).isEqualTo(endpoint.getAddress());
             assertThat(row.getInt("port")).isEqualTo(endpoint.getPort());
+            assertThat(row.getString("hostname")).isEqualTo(endpoint.getAddress().getHostAddress());
             assertThat(row.getInt("generation")).isEqualTo(localState.getHeartBeatState().getGeneration());
             assertThat(row.getInt("heartbeat")).isNotNull();