diff --git a/.circleci/config.yml b/.circleci/config.yml
index 05eb3a419b..42f01a2dd4 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -83,6 +83,17 @@ commands:
             echo "APT::Acquire::Retries \"10\";" | sudo tee -a /etc/apt/apt.conf.d/80-retries # llvm.org unreliable
             sudo apt-get update -y && sudo apt-get install -y clang-10
 
+  install-clang-13:
+    steps:
+      - run:
+          name: Install Clang 13
+          command: |
+            echo "deb http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main" | sudo tee -a /etc/apt/sources.list
+            echo "deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-13 main" | sudo tee -a /etc/apt/sources.list
+            echo "APT::Acquire::Retries \"10\";" | sudo tee -a /etc/apt/apt.conf.d/80-retries # llvm.org unreliable
+            wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
+            sudo apt-get update -y && sudo apt-get install -y clang-13
+
   install-gflags:
     steps:
       - run:
@@ -396,6 +407,16 @@ jobs:
       - run: CC=gcc-11 CXX=g++-11 V=1 SKIP_LINK=1 make -j16 all 2>&1 | .circleci/cat_ignore_eagain # Linking broken because libgflags compiled with newer ABI
       - post-steps
 
+  build-linux-clang-13-no_test_run:
+    machine:
+      image: ubuntu-2004:202010-01
+    resource_class: xlarge
+    steps:
+      - pre-steps
+      - install-clang-13
+      - run: CC=clang-13 CXX=clang++-13 USE_CLANG=1 make -j16 all 2>&1 | .circleci/cat_ignore_eagain
+      - post-steps
+
   # This job is only to make sure the microbench tests are able to run, the benchmark result is not meaningful as the CI host is changing.
   build-linux-microbench:
     machine:
@@ -792,6 +813,7 @@ workflows:
   build-linux-compilers-no_test_run:
     jobs:
       - build-linux-clang-no_test_run
+      - build-linux-clang-13-no_test_run
       - build-linux-gcc-4_8-no_test_run
       - build-linux-gcc-8-no_test_run
       - build-linux-gcc-9-no_test_run
diff --git a/db/compaction/compaction_picker_test.cc b/db/compaction/compaction_picker_test.cc
index 6b005db0b4..1c928ad4ab 100644
--- a/db/compaction/compaction_picker_test.cc
+++ b/db/compaction/compaction_picker_test.cc
@@ -964,13 +964,11 @@ TEST_F(CompactionPickerTest, NeedsCompactionFIFO) {
 
   // verify whether compaction is needed based on the current
   // size of L0 files.
-  uint64_t current_size = 0;
   for (int i = 1; i <= kFileCount; ++i) {
     NewVersionStorage(1, kCompactionStyleFIFO);
     Add(0, i, ToString((i + 100) * 1000).c_str(),
-        ToString((i + 100) * 1000 + 999).c_str(),
-        kFileSize, 0, i * 100, i * 100 + 99);
-    current_size += kFileSize;
+        ToString((i + 100) * 1000 + 999).c_str(), kFileSize, 0, i * 100,
+        i * 100 + 99);
     UpdateVersionStorageInfo();
     ASSERT_EQ(fifo_compaction_picker.NeedsCompaction(vstorage_.get()),
               vstorage_->CompactionScore(0) >= 1);
diff --git a/db/db_basic_test.cc b/db/db_basic_test.cc
index 81ac829b49..96687ba743 100644
--- a/db/db_basic_test.cc
+++ b/db/db_basic_test.cc
@@ -1892,7 +1892,6 @@ TEST_F(DBBasicTest, MultiGetBatchedValueSizeMultiLevelMerge) {
 
   ASSERT_EQ(values.size(), keys.size());
 
-  uint64_t curr_value_size = 0;
   for (unsigned int j = 0; j < 26; ++j) {
     int key = j + 10;
     std::string value;
@@ -1909,11 +1908,9 @@ TEST_F(DBBasicTest, MultiGetBatchedValueSizeMultiLevelMerge) {
       value.append(",");
       value.append("val_mem_" + std::to_string(key));
     }
-    curr_value_size += value.size();
     ASSERT_EQ(values[j], value);
     ASSERT_OK(statuses[j]);
   }
-  // ASSERT_TRUE(curr_value_size <= read_options.value_size_hard_limit);
 
   // All remaning keys status is set Status::Abort
   for (unsigned int j = 26; j < 40; j++) {
diff --git a/db/db_test2.cc b/db/db_test2.cc
index e09d05d45d..c123d7351a 100644
--- a/db/db_test2.cc
+++ b/db/db_test2.cc
@@ -2827,7 +2827,6 @@ TEST_F(DBTest2, ReadAmpBitmapLiveInCacheAfterDBClose) {
     Close();
     Reopen(options);
 
-    uint64_t total_useful_bytes = 0;
     std::set<int> read_keys;
     std::string value;
     // Iter1: Read half the DB, Read even keys
@@ -2838,8 +2837,6 @@ TEST_F(DBTest2, ReadAmpBitmapLiveInCacheAfterDBClose) {
 
       if (read_keys.find(i) == read_keys.end()) {
         auto internal_key = InternalKey(key, 0, ValueType::kTypeValue);
-        total_useful_bytes +=
-            GetEncodedEntrySize(internal_key.size(), value.size());
         read_keys.insert(i);
       }
     }
@@ -2866,8 +2863,6 @@ TEST_F(DBTest2, ReadAmpBitmapLiveInCacheAfterDBClose) {
 
       if (read_keys.find(i) == read_keys.end()) {
         auto internal_key = InternalKey(key, 0, ValueType::kTypeValue);
-        total_useful_bytes +=
-            GetEncodedEntrySize(internal_key.size(), value.size());
         read_keys.insert(i);
       }
     }
diff --git a/options/db_options.h b/options/db_options.h
index 5244460e89..d44331b06c 100644
--- a/options/db_options.h
+++ b/options/db_options.h
@@ -116,7 +116,6 @@ struct ImmutableDBOptions {
 struct MutableDBOptions {
   static const char* kName() { return "MutableDBOptions"; }
   MutableDBOptions();
-  explicit MutableDBOptions(const MutableDBOptions& options) = default;
   explicit MutableDBOptions(const DBOptions& options);
 
   void Dump(Logger* log) const;
diff --git a/utilities/env_mirror.cc b/utilities/env_mirror.cc
index 061b986324..3ea323b429 100644
--- a/utilities/env_mirror.cc
+++ b/utilities/env_mirror.cc
@@ -27,13 +27,17 @@ class SequentialFileMirror : public SequentialFile {
     if (as == Status::OK()) {
       char* bscratch = new char[n];
       Slice bslice;
+#ifndef NDEBUG
       size_t off = 0;
+#endif
       size_t left = aslice.size();
       while (left) {
         Status bs = b_->Read(left, &bslice, bscratch);
+#ifndef NDEBUG
         assert(as == bs);
         assert(memcmp(bscratch, scratch + off, bslice.size()) == 0);
         off += bslice.size();
+#endif
         left -= bslice.size();
       }
       delete[] bscratch;