diff --git a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/external/ExternalLibraryUtils.java b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/external/ExternalLibraryUtils.java
index 5f86c28..0e72976 100755
--- a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/external/ExternalLibraryUtils.java
+++ b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/external/ExternalLibraryUtils.java
@@ -247,7 +247,7 @@
                     }
                     Function f = new Function(dataverse, libraryName + "#" + function.getName().trim(), args.size(),
                             args, function.getReturnType().trim(), function.getDefinition().trim(),
-                            library.getLanguage().trim(), function.getFunctionType().trim());
+                            library.getLanguage().trim(), function.getFunctionType().trim(), 0);
                     MetadataManager.INSTANCE.addFunction(mdTxnCtx, f);
                     if (LOGGER.isLoggable(Level.INFO)) {
                         LOGGER.info("Installed function: " + libraryName + "#" + function.getName().trim());
diff --git a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
index e9c8cf7..f64812e 100644
--- a/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
+++ b/asterixdb/asterix-app/src/main/java/org/apache/asterix/app/translator/QueryTranslator.java
@@ -1642,9 +1642,10 @@
             if (dv == null) {
                 throw new AlgebricksException("There is no dataverse with this name " + dataverse + ".");
             }
+            // If the function body contains function calls, theirs reference count won't be increased.
             Function function = new Function(dataverse, functionName, cfs.getaAterixFunction().getArity(),
                     cfs.getParamList(), Function.RETURNTYPE_VOID, cfs.getFunctionBody(), Function.LANGUAGE_AQL,
-                    FunctionKind.SCALAR.toString());
+                    FunctionKind.SCALAR.toString(), 0);
             MetadataManager.INSTANCE.addFunction(mdTxnCtx, function);
 
             MetadataManager.INSTANCE.commitTransaction(mdTxnCtx);
@@ -1670,6 +1671,8 @@
                 if (!stmtDropFunction.getIfExists()) {
                     throw new AlgebricksException("Unknonw function " + signature);
                 }
+            } else if (function.getReferenceCount() != 0) {
+                throw new AlgebricksException("Function " + signature + " is being used. It cannot be dropped.");
             } else {
                 MetadataManager.INSTANCE.dropFunction(mdTxnCtx, signature);
             }
@@ -2153,6 +2156,13 @@
             fc = new FeedConnection(dataverseName, feedName, datasetName, appliedFunctions, policyName,
                     outputType.toString());
             MetadataManager.INSTANCE.addFeedConnection(metadataProvider.getMetadataTxnContext(), fc);
+            // Increase function reference count.
+            for (FunctionSignature funcSig : appliedFunctions) {
+                // The function should be cached in Metadata manager, so this operation is not that expensive.
+                Function func = MetadataManager.INSTANCE.getFunction(mdTxnCtx, funcSig);
+                func.reference();
+                MetadataManager.INSTANCE.updateFunction(mdTxnCtx, func);
+            }
             MetadataManager.INSTANCE.commitTransaction(mdTxnCtx);
         } catch (Exception e) {
             abort(e, e, mdTxnCtx);
@@ -2189,6 +2199,12 @@
                         + cfs.getDatasetName().getValue() + ". Invalid operation!");
             }
             MetadataManager.INSTANCE.dropFeedConnection(mdTxnCtx, dataverseName, feedName, datasetName);
+            for (FunctionSignature functionSignature : fc.getAppliedFunctions()) {
+                Function function = MetadataManager.INSTANCE.getFunction(mdTxnCtx, functionSignature);
+                function.dereference();
+                MetadataManager.INSTANCE.updateFunction(mdTxnCtx, function);
+            }
+            MetadataManager.INSTANCE.commitTransaction(mdTxnCtx);
         } catch (Exception e) {
             abort(e, e, mdTxnCtx);
             throw e;
diff --git a/asterixdb/asterix-app/src/test/resources/metadata/results/basic/meta06/meta06.1.adm b/asterixdb/asterix-app/src/test/resources/metadata/results/basic/meta06/meta06.1.adm
index 58f5b77..2131611 100644
--- a/asterixdb/asterix-app/src/test/resources/metadata/results/basic/meta06/meta06.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/metadata/results/basic/meta06/meta06.1.adm
@@ -1 +1 @@
-{ "DataverseName": "testdv", "Name": "fun01", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "\"This is an AQL Bodied UDF\"", "Language": "AQL", "Kind": "SCALAR" }
+{ "DataverseName": "testdv", "Name": "fun01", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "\"This is an AQL Bodied UDF\"", "Language": "AQL", "Kind": "SCALAR", "ReferenceCount": "0" }
diff --git a/asterixdb/asterix-app/src/test/resources/metadata/results/basic/metadata_datatype/metadata_datatype.1.adm b/asterixdb/asterix-app/src/test/resources/metadata/results/basic/metadata_datatype/metadata_datatype.1.adm
index 7229aa8..650c924 100644
--- a/asterixdb/asterix-app/src/test/resources/metadata/results/basic/metadata_datatype/metadata_datatype.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/metadata/results/basic/metadata_datatype/metadata_datatype.1.adm
@@ -29,7 +29,7 @@
 { "DataverseName": "Metadata", "DatatypeName": "FeedRecordType", "Derived": { "Tag": "RECORD", "IsAnonymous": false, "Record": { "IsOpen": true, "Fields": [ { "FieldName": "DataverseName", "FieldType": "string", "IsNullable": false }, { "FieldName": "FeedName", "FieldType": "string", "IsNullable": false }, { "FieldName": "AdapterName", "FieldType": "string", "IsNullable": false }, { "FieldName": "AdapterConfiguration", "FieldType": "FeedRecordType_AdapterConfiguration", "IsNullable": false }, { "FieldName": "Timestamp", "FieldType": "string", "IsNullable": false } ] } }, "Timestamp": "Fri Oct 21 10:29:22 PDT 2016" }
 { "DataverseName": "Metadata", "DatatypeName": "FeedRecordType_AdapterConfiguration", "Derived": { "Tag": "UNORDEREDLIST", "IsAnonymous": true, "UnorderedList": "FeedRecordType_AdapterConfiguration_Item" }, "Timestamp": "Fri Oct 21 10:29:22 PDT 2016" }
 { "DataverseName": "Metadata", "DatatypeName": "FeedRecordType_AdapterConfiguration_Item", "Derived": { "Tag": "RECORD", "IsAnonymous": true, "Record": { "IsOpen": true, "Fields": [ { "FieldName": "Name", "FieldType": "string", "IsNullable": false }, { "FieldName": "Value", "FieldType": "string", "IsNullable": false } ] } }, "Timestamp": "Fri Oct 21 10:29:22 PDT 2016" }
-{ "DataverseName": "Metadata", "DatatypeName": "FunctionRecordType", "Derived": { "Tag": "RECORD", "IsAnonymous": false, "Record": { "IsOpen": true, "Fields": [ { "FieldName": "DataverseName", "FieldType": "string", "IsNullable": false }, { "FieldName": "Name", "FieldType": "string", "IsNullable": false }, { "FieldName": "Arity", "FieldType": "string", "IsNullable": false }, { "FieldName": "Params", "FieldType": "FunctionRecordType_Params", "IsNullable": false }, { "FieldName": "ReturnType", "FieldType": "string", "IsNullable": false }, { "FieldName": "Definition", "FieldType": "string", "IsNullable": false }, { "FieldName": "Language", "FieldType": "string", "IsNullable": false }, { "FieldName": "Kind", "FieldType": "string", "IsNullable": false } ] } }, "Timestamp": "Fri Oct 21 10:29:22 PDT 2016" }
+{ "DataverseName": "Metadata", "DatatypeName": "FunctionRecordType", "Derived": { "Tag": "RECORD", "IsAnonymous": false, "Record": { "IsOpen": true, "Fields": [ { "FieldName": "DataverseName", "FieldType": "string", "IsNullable": false }, { "FieldName": "Name", "FieldType": "string", "IsNullable": false }, { "FieldName": "Arity", "FieldType": "string", "IsNullable": false }, { "FieldName": "Params", "FieldType": "FunctionRecordType_Params", "IsNullable": false }, { "FieldName": "ReturnType", "FieldType": "string", "IsNullable": false }, { "FieldName": "Definition", "FieldType": "string", "IsNullable": false }, { "FieldName": "Language", "FieldType": "string", "IsNullable": false }, { "FieldName": "Kind", "FieldType": "string", "IsNullable": false }, { "FieldName": "ReferenceCount", "FieldType": "string", "IsNullable": false } ] } }, "Timestamp": "Sun May 21 09:56:53 PDT 2017" }
 { "DataverseName": "Metadata", "DatatypeName": "FunctionRecordType_Params", "Derived": { "Tag": "ORDEREDLIST", "IsAnonymous": true, "OrderedList": "string" }, "Timestamp": "Fri Oct 21 10:29:22 PDT 2016" }
 { "DataverseName": "Metadata", "DatatypeName": "IndexRecordType", "Derived": { "Tag": "RECORD", "IsAnonymous": false, "Record": { "IsOpen": true, "Fields": [ { "FieldName": "DataverseName", "FieldType": "string", "IsNullable": false }, { "FieldName": "DatasetName", "FieldType": "string", "IsNullable": false }, { "FieldName": "IndexName", "FieldType": "string", "IsNullable": false }, { "FieldName": "IndexStructure", "FieldType": "string", "IsNullable": false }, { "FieldName": "SearchKey", "FieldType": "IndexRecordType_SearchKey", "IsNullable": false }, { "FieldName": "IsPrimary", "FieldType": "boolean", "IsNullable": false }, { "FieldName": "Timestamp", "FieldType": "string", "IsNullable": false }, { "FieldName": "PendingOp", "FieldType": "int32", "IsNullable": false } ] } }, "Timestamp": "Fri Oct 21 10:29:21 PDT 2016" }
 { "DataverseName": "Metadata", "DatatypeName": "IndexRecordType_SearchKey", "Derived": { "Tag": "ORDEREDLIST", "IsAnonymous": true, "OrderedList": "IndexRecordType_SearchKey_Item" }, "Timestamp": "Fri Oct 21 10:29:21 PDT 2016" }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.1.ddl.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.1.ddl.aql
new file mode 100644
index 0000000..19eda0e
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.1.ddl.aql
@@ -0,0 +1,44 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+drop dataverse experiments if exists;
+create dataverse experiments;
+use dataverse experiments;
+
+create type TwitterUser if not exists as open{
+    screen-name: string,
+    friends_count: int32,
+    name: string,
+    followers_count: int32
+};
+
+create dataset TwitterUsers(TwitterUser) primary key screen-name;
+
+create function test_func0($xyz) {
+    let $tty1 := if ($xyz.followers_count > 25000) then {"popularity":"Good!"} else {"popularity":"Bad!"}
+    return object_merge($tty1, $xyz)
+}
+
+create feed UserFeed using socket_adapter
+(
+    ("sockets"="127.0.0.1:10001"),
+    ("address-type"="IP"),
+    ("type-name"="TwitterUser"),
+    ("format"="adm"),
+    ("upsert-feed"="true")
+);
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.2.update.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.2.update.aql
new file mode 100644
index 0000000..f6c40de
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.2.update.aql
@@ -0,0 +1,24 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+use dataverse experiments;
+set wait-for-completion-feed "false";
+
+connect feed UserFeed to dataset TwitterUsers apply function test_func0;
+
+disconnect feed UserFeed from dataset TwitterUsers;
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.3.ddl.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.3.ddl.aql
new file mode 100644
index 0000000..624c628
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-no-longer-used-by-feed/drop-function-no-longer-used-by-feed.3.ddl.aql
@@ -0,0 +1,21 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+use dataverse experiments;
+drop function test_func0@1;
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.ddl.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.ddl.aql
new file mode 100644
index 0000000..19eda0e
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.ddl.aql
@@ -0,0 +1,44 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+drop dataverse experiments if exists;
+create dataverse experiments;
+use dataverse experiments;
+
+create type TwitterUser if not exists as open{
+    screen-name: string,
+    friends_count: int32,
+    name: string,
+    followers_count: int32
+};
+
+create dataset TwitterUsers(TwitterUser) primary key screen-name;
+
+create function test_func0($xyz) {
+    let $tty1 := if ($xyz.followers_count > 25000) then {"popularity":"Good!"} else {"popularity":"Bad!"}
+    return object_merge($tty1, $xyz)
+}
+
+create feed UserFeed using socket_adapter
+(
+    ("sockets"="127.0.0.1:10001"),
+    ("address-type"="IP"),
+    ("type-name"="TwitterUser"),
+    ("format"="adm"),
+    ("upsert-feed"="true")
+);
\ No newline at end of file
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.2.update.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.2.update.aql
new file mode 100644
index 0000000..4654612
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.2.update.aql
@@ -0,0 +1,23 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+use dataverse experiments;
+set wait-for-completion-feed "false";
+
+connect feed UserFeed to dataset TwitterUsers apply function test_func0;
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.3.ddl.aql b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.3.ddl.aql
new file mode 100644
index 0000000..624c628
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/queries/feeds/drop-function-used-by-feed/drop-function-used-by-feed.3.ddl.aql
@@ -0,0 +1,21 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+use dataverse experiments;
+drop function test_func0@1;
+
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.adm
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/feeds/drop-function-used-by-feed/drop-function-used-by-feed.1.adm
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/single-line-definition/single-line-definition.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/single-line-definition/single-line-definition.1.adm
index 5ba00ae..5545dfb 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/single-line-definition/single-line-definition.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/single-line-definition/single-line-definition.1.adm
@@ -1 +1 @@
-{ "DataverseName": "test", "Name": "printName", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "'AsterixDB Shared nothing parallel BDMS'", "Language": "AQL", "Kind": "SCALAR" }
+{ "DataverseName": "test", "Name": "printName", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "'AsterixDB Shared nothing parallel BDMS'", "Language": "AQL", "Kind": "SCALAR", "ReferenceCount": "0" }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/udf28/udf28.1.adm b/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/udf28/udf28.1.adm
index b106dbe..2bc8eaf 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/udf28/udf28.1.adm
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/results/user-defined-functions/udf28/udf28.1.adm
@@ -1 +1 @@
-{ "DataverseName": "test", "Name": "f1", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "100", "Language": "AQL", "Kind": "SCALAR" }
+{ "DataverseName": "test", "Name": "f1", "Arity": "0", "Params": [  ], "ReturnType": "VOID", "Definition": "100", "Language": "AQL", "Kind": "SCALAR", "ReferenceCount": "0" }
diff --git a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite.xml b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite.xml
index e2070c0..d5b8e74 100644
--- a/asterixdb/asterix-app/src/test/resources/runtimets/testsuite.xml
+++ b/asterixdb/asterix-app/src/test/resources/runtimets/testsuite.xml
@@ -279,6 +279,17 @@
         <expected-error>Cannot find function</expected-error>
       </compilation-unit>
     </test-case>
+    <test-case FilePath="feeds">
+      <compilation-unit name="drop-function-used-by-feed">
+        <output-dir compare="Text">drop-function-used-by-feed</output-dir>
+        <expected-error>Function experiments.test_func0@1 is being used. It cannot be dropped.</expected-error>
+      </compilation-unit>
+    </test-case>
+    <test-case FilePath="feeds">
+      <compilation-unit name="drop-function-no-longer-used-by-feed">
+        <output-dir compare="Text">drop-function-used-by-feed</output-dir>
+      </compilation-unit>
+    </test-case>
   </test-group>
   <test-group name="upsert">
     <test-case FilePath="upsert">
diff --git a/asterixdb/asterix-installer/src/test/resources/integrationts/library/results/library-metadata/functionDataset/functionDataset.1.adm b/asterixdb/asterix-installer/src/test/resources/integrationts/library/results/library-metadata/functionDataset/functionDataset.1.adm
index ef563f1..52fb855 100644
--- a/asterixdb/asterix-installer/src/test/resources/integrationts/library/results/library-metadata/functionDataset/functionDataset.1.adm
+++ b/asterixdb/asterix-installer/src/test/resources/integrationts/library/results/library-metadata/functionDataset/functionDataset.1.adm
@@ -1,8 +1,8 @@
-{ "DataverseName": "externallibtest", "Name": "testlib#addHashTags", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#addHashTagsInPlace", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsInPlaceFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#allTypes", "Arity": "1", "Params": [ "AllType" ], "ReturnType": "AllType", "Definition": "org.apache.asterix.external.library.AllTypesFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#echoDelay", "Arity": "1", "Params": [ "TweetMessageType" ], "ReturnType": "TweetMessageType", "Definition": "org.apache.asterix.external.library.EchoDelayFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#getCapital", "Arity": "1", "Params": [ "ASTRING" ], "ReturnType": "CountryCapitalType", "Definition": "org.apache.asterix.external.library.CapitalFinderFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#mysum", "Arity": "2", "Params": [ "AINT32", "AINT32" ], "ReturnType": "AINT32", "Definition": "org.apache.asterix.external.library.SumFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#parseTweet", "Arity": "1", "Params": [ "TweetInputType" ], "ReturnType": "TweetOutputType", "Definition": "org.apache.asterix.external.library.ParseTweetFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "testlib#toUpper", "Arity": "1", "Params": [ "TextType" ], "ReturnType": "TextType", "Definition": "org.apache.asterix.external.library.UpperCaseFactory", "Language": "JAVA", "Kind": "SCALAR" }
+{ "DataverseName": "externallibtest", "Name": "testlib#addHashTags", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#addHashTagsInPlace", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsInPlaceFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#allTypes", "Arity": "1", "Params": [ "AllType" ], "ReturnType": "AllType", "Definition": "org.apache.asterix.external.library.AllTypesFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#echoDelay", "Arity": "1", "Params": [ "TweetMessageType" ], "ReturnType": "TweetMessageType", "Definition": "org.apache.asterix.external.library.EchoDelayFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#getCapital", "Arity": "1", "Params": [ "ASTRING" ], "ReturnType": "CountryCapitalType", "Definition": "org.apache.asterix.external.library.CapitalFinderFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#mysum", "Arity": "2", "Params": [ "AINT32", "AINT32" ], "ReturnType": "AINT32", "Definition": "org.apache.asterix.external.library.SumFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#parseTweet", "Arity": "1", "Params": [ "TweetInputType" ], "ReturnType": "TweetOutputType", "Definition": "org.apache.asterix.external.library.ParseTweetFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "testlib#toUpper", "Arity": "1", "Params": [ "TextType" ], "ReturnType": "TextType", "Definition": "org.apache.asterix.external.library.UpperCaseFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataManager.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataManager.java
index b2c2e81..05bf08e 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataManager.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataManager.java
@@ -558,6 +558,17 @@
     }
 
     @Override
+    public void updateFunction(MetadataTransactionContext mdTxnCtx, Function function) throws MetadataException {
+        try {
+            metadataNode.updateFunction(mdTxnCtx.getJobId(), function);
+        } catch (RemoteException e) {
+            throw new MetadataException(e);
+        }
+        mdTxnCtx.dropFunction(function);
+        mdTxnCtx.addFunction(function);
+    }
+
+    @Override
     public void addFunction(MetadataTransactionContext mdTxnCtx, Function function) throws MetadataException {
         try {
             metadataNode.addFunction(mdTxnCtx.getJobId(), function);
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataNode.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataNode.java
index c4c5098..ea7a47c 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataNode.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataNode.java
@@ -1866,4 +1866,24 @@
             throw new MetadataException(e);
         }
     }
+
+    @Override
+    public void updateFunction(JobId jobId, Function function) throws MetadataException, RemoteException {
+        try {
+            // remove old function
+            ITupleReference searchKey;
+            searchKey = createTuple(function.getDataverseName(), function.getName(),
+                    Integer.toString(function.getArity()));
+            ITupleReference functionTuple = getTupleToBeDeleted(jobId, MetadataPrimaryIndexes.FUNCTION_DATASET,
+                    searchKey);
+            deleteTupleFromIndex(jobId, MetadataPrimaryIndexes.FUNCTION_DATASET, functionTuple);
+            // add new function
+            FunctionTupleTranslator functionTupleTranslator = tupleTranslatorProvider.getFunctionTupleTranslator(true);
+            functionTuple = functionTupleTranslator.getTupleFromMetadataEntity(function);
+            insertTupleIntoIndex(jobId, MetadataPrimaryIndexes.FUNCTION_DATASET, functionTuple);
+        } catch (HyracksDataException | ACIDException e) {
+            throw new MetadataException(e);
+        }
+
+    }
 }
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataTransactionContext.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataTransactionContext.java
index b2ec7f2..d8bf559 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataTransactionContext.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/MetadataTransactionContext.java
@@ -158,7 +158,7 @@
 
     public void dropFunction(FunctionSignature signature) {
         Function function = new Function(signature.getNamespace(), signature.getName(), signature.getArity(), null,
-                null, null, null, null);
+                null, null, null, null, 0);
         droppedCache.addFunctionIfNotExists(function);
         logAndApply(new MetadataLogicalOperation(function, false));
     }
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataManager.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataManager.java
index 8ce53d0..f36d510 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataManager.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataManager.java
@@ -397,6 +397,8 @@
      */
     void dropFunction(MetadataTransactionContext ctx, FunctionSignature functionSignature) throws MetadataException;
 
+    void updateFunction(MetadataTransactionContext ctx, Function function) throws MetadataException;
+
     /**
      * @param mdTxnCtx
      *            MetadataTransactionContext of an active metadata transaction.
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataNode.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataNode.java
index 21b170d..c4ae70c 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataNode.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/api/IMetadataNode.java
@@ -426,6 +426,8 @@
      */
     void addFunction(JobId jobId, Function function) throws MetadataException, RemoteException;
 
+    void updateFunction(JobId jobId, Function function) throws MetadataException, RemoteException;
+
     /**
      * @param ctx
      * @param dataverseName
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/bootstrap/MetadataRecordTypes.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/bootstrap/MetadataRecordTypes.java
index 2a04b58..852c01f 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/bootstrap/MetadataRecordTypes.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/bootstrap/MetadataRecordTypes.java
@@ -99,6 +99,7 @@
     public static final String FIELD_NAME_VALUE = "Value";
     public static final String FIELD_NAME_WORKING_MEMORY_SIZE = "WorkingMemorySize";
     public static final String FIELD_NAME_APPLIED_FUNCTIONS = "AppliedFunctions";
+    public static final String FIELD_NAME_REFERENCE_COUNT = "ReferenceCount";
 
     //---------------------------------- Record Types Creation ----------------------------------//
     //--------------------------------------- Properties ----------------------------------------//
@@ -321,16 +322,18 @@
     public static final int FUNCTION_ARECORD_FUNCTION_DEFINITION_FIELD_INDEX = 5;
     public static final int FUNCTION_ARECORD_FUNCTION_LANGUAGE_FIELD_INDEX = 6;
     public static final int FUNCTION_ARECORD_FUNCTION_KIND_FIELD_INDEX = 7;
+    public static final int FUNCTION_ARECORD_FUNCTION_REFERENCE_COUNT_INDEX = 8;
     public static final ARecordType FUNCTION_RECORDTYPE = createRecordType(
             // RecordTypeName
             RECORD_NAME_FUNCTION,
             // FieldNames
             new String[] { FIELD_NAME_DATAVERSE_NAME, FIELD_NAME_NAME, FIELD_NAME_ARITY, FIELD_NAME_PARAMS,
-                    FIELD_NAME_RETURN_TYPE, FIELD_NAME_DEFINITION, FIELD_NAME_LANGUAGE, FIELD_NAME_KIND },
+                    FIELD_NAME_RETURN_TYPE, FIELD_NAME_DEFINITION, FIELD_NAME_LANGUAGE, FIELD_NAME_KIND,
+                    FIELD_NAME_REFERENCE_COUNT },
             // FieldTypes
             new IAType[] { BuiltinType.ASTRING, BuiltinType.ASTRING, BuiltinType.ASTRING,
                     new AOrderedListType(BuiltinType.ASTRING, null), BuiltinType.ASTRING, BuiltinType.ASTRING,
-                    BuiltinType.ASTRING, BuiltinType.ASTRING },
+                    BuiltinType.ASTRING, BuiltinType.ASTRING, BuiltinType.ASTRING },
             //IsOpen?
             true);
     //------------------------------------------ Adapter ----------------------------------------//
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entities/Function.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entities/Function.java
index 7ff423c..b010a8a 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entities/Function.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entities/Function.java
@@ -19,6 +19,7 @@
 package org.apache.asterix.metadata.entities;
 
 import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
 
 import org.apache.asterix.metadata.MetadataCache;
 import org.apache.asterix.metadata.api.IMetadataEntity;
@@ -39,9 +40,10 @@
     private final String returnType;
     private final String language;
     private final String kind;
+    private AtomicInteger referenceCount;
 
     public Function(String dataverseName, String functionName, int arity, List<String> params, String returnType,
-            String functionBody, String language, String functionKind) {
+            String functionBody, String language, String functionKind, int referenceCount) {
         this.dataverse = dataverseName;
         this.name = functionName;
         this.params = params;
@@ -50,6 +52,7 @@
         this.language = language;
         this.kind = functionKind;
         this.arity = arity;
+        this.referenceCount = new AtomicInteger(referenceCount);
     }
 
     public String getDataverseName() {
@@ -94,4 +97,15 @@
         return cache.dropFunction(this);
     }
 
+    public int getReferenceCount() {
+        return referenceCount.get();
+    }
+
+    public int reference() {
+        return referenceCount.incrementAndGet();
+    }
+
+    public int dereference() {
+        return referenceCount.decrementAndGet();
+    }
 }
diff --git a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entitytupletranslators/FunctionTupleTranslator.java b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entitytupletranslators/FunctionTupleTranslator.java
index 64c4035..7cbc6ac 100644
--- a/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entitytupletranslators/FunctionTupleTranslator.java
+++ b/asterixdb/asterix-metadata/src/main/java/org/apache/asterix/metadata/entitytupletranslators/FunctionTupleTranslator.java
@@ -104,8 +104,10 @@
         String functionKind =
                 ((AString) functionRecord.getValueByPos(MetadataRecordTypes.FUNCTION_ARECORD_FUNCTION_KIND_FIELD_INDEX))
                         .getStringValue();
+        String referenceCount = ((AString) functionRecord
+                .getValueByPos(MetadataRecordTypes.FUNCTION_ARECORD_FUNCTION_REFERENCE_COUNT_INDEX)).getStringValue();
         return new Function(dataverseName, functionName, Integer.parseInt(arity), params, returnType, definition,
-                language, functionKind);
+                language, functionKind, Integer.parseInt(referenceCount));
 
     }
 
@@ -185,6 +187,12 @@
         stringSerde.serialize(aString, fieldValue.getDataOutput());
         recordBuilder.addField(MetadataRecordTypes.FUNCTION_ARECORD_FUNCTION_KIND_FIELD_INDEX, fieldValue);
 
+        // write field 8
+        fieldValue.reset();
+        aString.setValue(Integer.toString(function.getReferenceCount()));
+        stringSerde.serialize(aString, fieldValue.getDataOutput());
+        recordBuilder.addField(MetadataRecordTypes.FUNCTION_ARECORD_FUNCTION_REFERENCE_COUNT_INDEX, fieldValue);
+
         // write record
         recordBuilder.write(tupleBuilder.getDataOutput(), true);
         tupleBuilder.addFieldEndOffset();
diff --git a/asterixdb/asterix-yarn/src/test/resources/library/results/library-metadata/functionDataset/functionDataset.1.adm b/asterixdb/asterix-yarn/src/test/resources/library/results/library-metadata/functionDataset/functionDataset.1.adm
index 0675316..cdf7792 100644
--- a/asterixdb/asterix-yarn/src/test/resources/library/results/library-metadata/functionDataset/functionDataset.1.adm
+++ b/asterixdb/asterix-yarn/src/test/resources/library/results/library-metadata/functionDataset/functionDataset.1.adm
@@ -1,8 +1,8 @@
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#addHashTags", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#addHashTagsInPlace", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsInPlaceFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#allTypes", "Arity": "1", "Params": [ "AllType" ], "ReturnType": "AllType", "Definition": "org.apache.asterix.external.library.AllTypesFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#echoDelay", "Arity": "1", "Params": [ "TweetMessageType" ], "ReturnType": "TweetMessageType", "Definition": "org.apache.asterix.external.library.EchoDelayFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#getCapital", "Arity": "1", "Params": [ "ASTRING" ], "ReturnType": "CountryCapitalType", "Definition": "org.apache.asterix.external.library.CapitalFinderFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#mysum", "Arity": "2", "Params": [ "AINT32", "AINT32" ], "ReturnType": "AINT32", "Definition": "org.apache.asterix.external.library.SumFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#parseTweet", "Arity": "1", "Params": [ "TweetInputType" ], "ReturnType": "TweetOutputType", "Definition": "org.apache.asterix.external.library.ParseTweetFactory", "Language": "JAVA", "Kind": "SCALAR" }
-{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#toUpper", "Arity": "1", "Params": [ "TextType" ], "ReturnType": "TextType", "Definition": "org.apache.asterix.external.library.UpperCaseFactory", "Language": "JAVA", "Kind": "SCALAR" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#addHashTags", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#addHashTagsInPlace", "Arity": "1", "Params": [ "Tweet" ], "ReturnType": "ProcessedTweet", "Definition": "org.apache.asterix.external.library.AddHashTagsInPlaceFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#allTypes", "Arity": "1", "Params": [ "AllType" ], "ReturnType": "AllType", "Definition": "org.apache.asterix.external.library.AllTypesFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#echoDelay", "Arity": "1", "Params": [ "TweetMessageType" ], "ReturnType": "TweetMessageType", "Definition": "org.apache.asterix.external.library.EchoDelayFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#getCapital", "Arity": "1", "Params": [ "ASTRING" ], "ReturnType": "CountryCapitalType", "Definition": "org.apache.asterix.external.library.CapitalFinderFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#mysum", "Arity": "2", "Params": [ "AINT32", "AINT32" ], "ReturnType": "AINT32", "Definition": "org.apache.asterix.external.library.SumFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#parseTweet", "Arity": "1", "Params": [ "TweetInputType" ], "ReturnType": "TweetOutputType", "Definition": "org.apache.asterix.external.library.ParseTweetFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }
+{ "DataverseName": "externallibtest", "Name": "asterix-external-data-testlib#toUpper", "Arity": "1", "Params": [ "TextType" ], "ReturnType": "TextType", "Definition": "org.apache.asterix.external.library.UpperCaseFactory", "Language": "JAVA", "Kind": "SCALAR", "ReferenceCount": "0" }