diff --git a/docs/content/development/extensions-core/namespaced-lookup.md b/docs/content/development/extensions-core/namespaced-lookup.md
index 43677cf9401e..f98295d82a44 100644
--- a/docs/content/development/extensions-core/namespaced-lookup.md
+++ b/docs/content/development/extensions-core/namespaced-lookup.md
@@ -61,7 +61,7 @@ Cached namespace lookups can be specified as part of the [cluster wide config fo
        "tsColumn": "timeColumn"
     },
     "firstCacheTimeout": 120000,
-    "oneToOne":true
+    "injective":true
 }
  ```
 
@@ -70,7 +70,7 @@ The parameters are as follows
 |--------|-----------|--------|-------|
 |`extractionNamespace`|Specifies how to populate the local cache. See below|Yes|-|
 |`firstCacheTimeout`|How long to wait (in ms) for the first run of the cache to populate. 0 indicates to not wait|No|`60000` (1 minute)|
-|`oneToOne`|If the underlying map is injective (keys and values are unique) then optimizations can occur internally by setting this to `true`|No|`false`|
+|`injective`|If the underlying map is injective (keys and values are unique) then optimizations can occur internally by setting this to `true`|No|`false`|
 
 Proper functionality of Namespaced lookups requires the following extension to be loaded on the broker, peon, and historical nodes: 
 `druid-namespace-lookup`
@@ -87,6 +87,10 @@ setting namespaces (broker, peon, historical)
 The cache is populated in different ways depending on the settings below. In general, most namespaces employ 
 a `pollPeriod` at the end of which time they poll the remote resource of interest for updates.
 
+`onHeap` uses `ConcurrentMap`s in the java heap, and thus affects garbage collection and heap sizing.
+`offHeap` uses a 10MB on-heap buffer and MapDB using memory-mapped files in the java temporary directory.
+So if total `cachedNamespace` lookup size is in excess of 10MB, the extra will be kept in memory as page cache, and paged in and out by general OS tunings.
+
 # Supported Lookups
 
 For additional lookups, please see our [extensions list](../extensions.html).
diff --git a/extensions-core/kafka-extraction-namespace/src/main/java/io/druid/query/lookup/KafkaLookupExtractorFactory.java b/extensions-core/kafka-extraction-namespace/src/main/java/io/druid/query/lookup/KafkaLookupExtractorFactory.java
index f40d234b9a64..341ef046148f 100644
--- a/extensions-core/kafka-extraction-namespace/src/main/java/io/druid/query/lookup/KafkaLookupExtractorFactory.java
+++ b/extensions-core/kafka-extraction-namespace/src/main/java/io/druid/query/lookup/KafkaLookupExtractorFactory.java
@@ -103,7 +103,7 @@ public KafkaLookupExtractorFactory(
       @JsonProperty("kafkaTopic") final String kafkaTopic,
       @JsonProperty("kafkaProperties") final Map<String, String> kafkaProperties,
       @JsonProperty("connectTimeout") @Min(0) long connectTimeout,
-      @JsonProperty("isOneToOne") boolean isOneToOne
+      @JsonProperty("isInjective") boolean isOneToOne
   )
   {
     this.kafkaTopic = Preconditions.checkNotNull(kafkaTopic, "kafkaTopic required");
diff --git a/extensions-core/namespace-lookup/src/main/java/io/druid/query/lookup/NamespaceLookupExtractorFactory.java b/extensions-core/namespace-lookup/src/main/java/io/druid/query/lookup/NamespaceLookupExtractorFactory.java
index b9bab1be0422..3c8a0e9eac89 100644
--- a/extensions-core/namespace-lookup/src/main/java/io/druid/query/lookup/NamespaceLookupExtractorFactory.java
+++ b/extensions-core/namespace-lookup/src/main/java/io/druid/query/lookup/NamespaceLookupExtractorFactory.java
@@ -72,7 +72,7 @@ public class NamespaceLookupExtractorFactory implements LookupExtractorFactory
   private final LookupIntrospectHandler lookupIntrospectHandler;
   private final ExtractionNamespace extractionNamespace;
   private final long firstCacheTimeout;
-  private final boolean oneToOne;
+  private final boolean injective;
 
   private final String extractorID;
 
@@ -80,7 +80,7 @@ public class NamespaceLookupExtractorFactory implements LookupExtractorFactory
   public NamespaceLookupExtractorFactory(
       @JsonProperty("extractionNamespace") ExtractionNamespace extractionNamespace,
       @JsonProperty("firstCacheTimeout") Long firstCacheTimeout,
-      @JsonProperty("oneToOne") boolean oneToOne,
+      @JsonProperty("injective") boolean injective,
       @JacksonInject final NamespaceExtractionCacheManager manager
   )
   {
@@ -90,7 +90,7 @@ public NamespaceLookupExtractorFactory(
     );
     this.firstCacheTimeout = firstCacheTimeout == null ? DEFAULT_SCHEDULE_TIMEOUT : firstCacheTimeout;
     Preconditions.checkArgument(this.firstCacheTimeout >= 0);
-    this.oneToOne = oneToOne;
+    this.injective = injective;
     this.manager = manager;
     this.extractorID = buildID();
     this.lookupIntrospectHandler = new LookupIntrospectHandler()
@@ -207,7 +207,7 @@ public boolean replaces(@Nullable LookupExtractorFactory other)
   {
     if (other != null && other instanceof NamespaceLookupExtractorFactory) {
       NamespaceLookupExtractorFactory that = (NamespaceLookupExtractorFactory) other;
-      if (isOneToOne() != ((NamespaceLookupExtractorFactory) other).isOneToOne()) {
+      if (isInjective() != ((NamespaceLookupExtractorFactory) other).isInjective()) {
         return true;
       }
       if (getFirstCacheTimeout() != ((NamespaceLookupExtractorFactory) other).getFirstCacheTimeout()) {
@@ -237,9 +237,9 @@ public long getFirstCacheTimeout()
   }
 
   @JsonProperty
-  public boolean isOneToOne()
+  public boolean isInjective()
   {
-    return oneToOne;
+    return injective;
   }
 
   private String buildID()
@@ -275,7 +275,7 @@ public LookupExtractor get()
       } while (!preVersion.equals(postVersion));
       final byte[] v = StringUtils.toUtf8(postVersion);
       final byte[] id = StringUtils.toUtf8(extractorID);
-      return new MapLookupExtractor(map, isOneToOne())
+      return new MapLookupExtractor(map, isInjective())
       {
         @Override
         public byte[] getCacheKey()