HDFS-16550. Allow JN edit cache size to be set as a fraction of heap …

…memory (#4209)

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -1424,7 +1424,10 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final long DFS_JOURNALNODE_SYNC_INTERVAL_DEFAULT = 2*60*1000L;
   public static final String DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY =
       "dfs.journalnode.edit-cache-size.bytes";
-  public static final int DFS_JOURNALNODE_EDIT_CACHE_SIZE_DEFAULT = 1024 * 1024;
+
+  public static final String DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY =
+          "dfs.journalnode.edit-cache-size.fraction";
+  public static final float DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_DEFAULT = 0.5f;
 
   // Journal-node related configs for the client side.
   public static final String  DFS_QJOURNAL_QUEUE_SIZE_LIMIT_KEY = "dfs.qjournal.queued-edits.limit.mb";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/qjournal/server/JournaledEditsCache.java

@@ -40,6 +40,7 @@
 import org.apache.hadoop.hdfs.server.namenode.FSEditLogLoader;
 import org.apache.hadoop.hdfs.server.namenode.FSEditLogOp;
 import org.apache.hadoop.util.AutoCloseableLock;
+import org.apache.hadoop.util.Preconditions;
 
 /**
  * An in-memory cache of edits in their serialized form. This is used to serve
@@ -121,12 +122,18 @@ class JournaledEditsCache {
   // ** End lock-protected fields **
 
   JournaledEditsCache(Configuration conf) {
+    float fraction = conf.getFloat(DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY,
+        DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_DEFAULT);
+    Preconditions.checkArgument((fraction > 0 && fraction < 1.0f),
+        String.format("Cache config %s is set at %f, it should be a positive float value, " +
+            "less than 1.0. The recommended value is less than 0.9.",
+            DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY, fraction));
     capacity = conf.getInt(DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY,
-        DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_DEFAULT);
+        (int) (Runtime.getRuntime().maxMemory() * fraction));
     if (capacity > 0.9 * Runtime.getRuntime().maxMemory()) {
       Journal.LOG.warn(String.format("Cache capacity is set at %d bytes but " +
           "maximum JVM memory is only %d bytes. It is recommended that you " +
-          "decrease the cache size or increase the heap size.",
+          "decrease the cache size/fraction or increase the heap size.",
           capacity, Runtime.getRuntime().maxMemory()));
     }
     Journal.LOG.info("Enabling the journaled edits cache with a capacity " +
@@ -277,11 +284,12 @@ void storeEdits(byte[] inputData, long newStartTxn, long newEndTxn,
         initialize(INVALID_TXN_ID);
         Journal.LOG.warn(String.format("A single batch of edits was too " +
                 "large to fit into the cache: startTxn = %d, endTxn = %d, " +
-                "input length = %d. The capacity of the cache (%s) must be " +
+                "input length = %d. The cache size (%s) or cache fraction (%s) must be " +
                 "increased for it to work properly (current capacity %d)." +
                 "Cache is now empty.",
             newStartTxn, newEndTxn, inputData.length,
-            DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY, capacity));
+            DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY,
+            DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY, capacity));
         return;
       }
       if (dataMap.isEmpty()) {
@@ -388,10 +396,11 @@ private CacheMissException getCacheMissException(long requestedTxnId) {
     } else {
       return new CacheMissException(lowestTxnId - requestedTxnId,
           "Oldest txn ID available in the cache is %d, but requested txns " +
-              "starting at %d. The cache size (%s) may need to be increased " +
-              "to hold more transactions (currently %d bytes containing %d " +
+              "starting at %d. The cache size (%s) or cache fraction (%s) may need to be " +
+              "increased to hold more transactions (currently %d bytes containing %d " +
               "transactions)", lowestTxnId, requestedTxnId,
-          DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY, capacity,
+              DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY,
+              DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY, capacity,
           highestTxnId - lowestTxnId + 1);
     }
   }
@@ -414,4 +423,9 @@ long getCacheMissAmount() {
 
   }
 
+  @VisibleForTesting
+  int getCapacity() {
+    return capacity;
+  }
+
 }

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -4945,7 +4945,7 @@
 
 <property>
   <name>dfs.journalnode.edit-cache-size.bytes</name>
-  <value>1048576</value>
+  <value></value>
   <description>
     The size, in bytes, of the in-memory cache of edits to keep on the
     JournalNode. This cache is used to serve edits for tailing via the RPC-based
@@ -4955,6 +4955,22 @@
   </description>
 </property>
 
+<property>
+  <name>dfs.journalnode.edit-cache-size.fraction</name>
+  <value>0.5f</value>
+  <description>
+    This ratio refers to the proportion of the maximum memory of the JVM.
+    Used to calculate the size of the edits cache that is kept in the JournalNode's memory.
+    This config is an alternative to the dfs.journalnode.edit-cache-size.bytes.
+    And it is used to serve edits for tailing via the RPC-based mechanism, and is only
+    enabled when dfs.ha.tail-edits.in-progress is true. Transactions range in size but
+    are around 200 bytes on average, so the default of 1MB can store around 5000 transactions.
+    So we can configure a reasonable value based on the maximum memory. The recommended value
+    is less than 0.9. If we set dfs.journalnode.edit-cache-size.bytes, this parameter will
+    not take effect.
+  </description>
+</property>
+
 <property>
   <name>dfs.journalnode.kerberos.internal.spnego.principal</name>
   <value></value>

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/HDFSHighAvailabilityWithQJM.md

@@ -502,6 +502,16 @@ lag time will be much longer. The relevant configurations are:
     the oldest data in the cache was at transaction ID 20, a value of 10 would be added to the
     average.
 
+*   **dfs.journalnode.edit-cache-size.fraction** - This fraction refers to the proportion of
+    the maximum memory of the JVM. Used to calculate the size of the edits cache that is
+    kept in the JournalNode's memory. This config is an alternative to the
+    dfs.journalnode.edit-cache-size.bytes. And it is used to serve edits for tailing via
+    the RPC-based mechanism, and is only enabled when dfs.ha.tail-edits.in-progress is true.
+    Transactions range in size but are around 200 bytes on average, so the default of 1MB
+    can store around 5000 transactions. So we can configure a reasonable value based on
+    the maximum memory. The recommended value is less than 0.9. If we set
+    dfs.journalnode.edit-cache-size.bytes, this parameter will not take effect.
+
 This feature is primarily useful in conjunction with the Standby/Observer Read feature. Using this
 feature, read requests can be serviced from non-active NameNodes; thus tailing in-progress edits
 provides these nodes with the ability to serve requests with data which is much more fresh. See the

hadoop-hdfs-project/hadoop-hdfs/src/site/markdown/ObserverNameNode.md

@@ -194,6 +194,24 @@ few configurations to your **hdfs-site.xml**:
           <value>1048576</value>
         </property>
 
+*  **dfs.journalnode.edit-cache-size.fraction** - the fraction refers to
+   the proportion of the maximum memory of the JVM.
+
+   Used to calculate the size of the edits cache that
+   is kept in the JournalNode's memory.
+   This config is an alternative to the dfs.journalnode.edit-cache-size.bytes.
+   And it is used to serve edits for tailing via the RPC-based mechanism, and is only
+   enabled when dfs.ha.tail-edits.in-progress is true. Transactions range in size but
+   are around 200 bytes on average, so the default of 1MB can store around 5000 transactions.
+   So we can configure a reasonable value based on the maximum memory. The recommended value
+   is less than 0.9. If we set dfs.journalnode.edit-cache-size.bytes, this parameter will
+   not take effect.
+
+        <property>
+          <name>dfs.journalnode.edit-cache-size.fraction</name>
+          <value>0.5f</value>
+        </property>
+
 *  **dfs.namenode.accesstime.precision** -- whether to enable access
    time for HDFS file.
 

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/qjournal/server/TestJournaledEditsCache.java

@@ -221,6 +221,27 @@ public void testCacheMalformedInput() throws Exception {
     cache.retrieveEdits(-1, 10, new ArrayList<>());
   }
 
+  @Test
+  public void testCacheSizeConfigs() {
+    // Assert the default configs.
+    Configuration config = new Configuration();
+    cache = new JournaledEditsCache(config);
+    assertEquals((int) (Runtime.getRuntime().maxMemory() * 0.5f), cache.getCapacity());
+
+    // Set dfs.journalnode.edit-cache-size.bytes.
+    Configuration config1 = new Configuration();
+    config1.setInt(DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_KEY, 1);
+    config1.setFloat(DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY, 0.1f);
+    cache = new JournaledEditsCache(config1);
+    assertEquals(1, cache.getCapacity());
+
+    // Don't set dfs.journalnode.edit-cache-size.bytes.
+    Configuration config2 = new Configuration();
+    config2.setFloat(DFSConfigKeys.DFS_JOURNALNODE_EDIT_CACHE_SIZE_FRACTION_KEY, 0.1f);
+    cache = new JournaledEditsCache(config2);
+    assertEquals((int) (Runtime.getRuntime().maxMemory() * 0.1f), cache.getCapacity());
+  }
+
   private void storeEdits(int startTxn, int endTxn) throws Exception {
     cache.storeEdits(createTxnData(startTxn, endTxn - startTxn + 1), startTxn,
         endTxn, NameNodeLayoutVersion.CURRENT_LAYOUT_VERSION);