Add column family information to WAL

Summary:
I have added three new value types:
* kTypeColumnFamilyDeletion
* kTypeColumnFamilyValue
* kTypeColumnFamilyMerge
which include column family Varint32 before the data (value, deletion and merge). These values are used only in WAL (not in memtables yet).

This endeavour required changing some WriteBatch internals.

Test Plan: Added a unittest

Reviewers: dhruba, haobo, sdong, kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D15045

include/rocksdb/write_batch.h

@@ -40,33 +40,31 @@ class WriteBatch {
   ~WriteBatch();
 
   // Store the mapping "key->value" in the database.
-  void Put(const ColumnFamilyHandle& column_family, const Slice& key,
-           const Slice& value);
+  void Put(uint32_t column_family_id, const Slice& key, const Slice& value);
   void Put(const Slice& key, const Slice& value) {
-    Put(default_column_family, key, value);
+    Put(0, key, value);
   }
 
   // Variant of Put() that gathers output like writev(2).  The key and value
   // that will be written to the database are concatentations of arrays of
   // slices.
-  void Put(const ColumnFamilyHandle& column_family, const SliceParts& key,
+  void Put(uint32_t column_family_id, const SliceParts& key,
            const SliceParts& value);
   void Put(const SliceParts& key, const SliceParts& value) {
-    Put(default_column_family, key, value);
+    Put(0, key, value);
   }
 
   // Merge "value" with the existing value of "key" in the database.
   // "key->merge(existing, value)"
-  void Merge(const ColumnFamilyHandle& column_family, const Slice& key,
-             const Slice& value);
+  void Merge(uint32_t column_family_id, const Slice& key, const Slice& value);
   void Merge(const Slice& key, const Slice& value) {
-    Merge(default_column_family, key, value);
+    Merge(0, key, value);
   }
 
   // If the database contains a mapping for "key", erase it.  Else do nothing.
-  void Delete(const ColumnFamilyHandle& column_family, const Slice& key);
+  void Delete(uint32_t column_family_id, const Slice& key);
   void Delete(const Slice& key) {
-    Delete(default_column_family, key);
+    Delete(0, key);
   }
 
   // Append a blob of arbitrary size to the records in this batch. The blob will
@@ -89,25 +87,31 @@ class WriteBatch {
    public:
     virtual ~Handler();
     // default implementation will just call Put without column family for
-    // backwards compatibility
-    virtual void PutCF(const ColumnFamilyHandle& column_family,
-                       const Slice& key, const Slice& value) {
-      Put(key, value);
+    // backwards compatibility. If the column family is not default,
+    // the function is noop
+    virtual void PutCF(uint32_t column_family_id, const Slice& key,
+                       const Slice& value) {
+      if (column_family_id == 0) {
+        Put(key, value);
+      }
     }
     virtual void Put(const Slice& key, const Slice& value);
     // Merge and LogData are not pure virtual. Otherwise, we would break
     // existing clients of Handler on a source code level. The default
     // implementation of Merge simply throws a runtime exception.
-    virtual void MergeCF(const ColumnFamilyHandle& column_family,
-                         const Slice& key, const Slice& value) {
-      Merge(key, value);
+    virtual void MergeCF(uint32_t column_family_id, const Slice& key,
+                         const Slice& value) {
+      if (column_family_id == 0) {
+        Merge(key, value);
+      }
     }
     virtual void Merge(const Slice& key, const Slice& value);
     // The default implementation of LogData does nothing.
     virtual void LogData(const Slice& blob);
-    virtual void DeleteCF(const ColumnFamilyHandle& column_family,
-                          const Slice& key) {
-      Delete(key);
+    virtual void DeleteCF(uint32_t column_family_id, const Slice& key) {
+      if (column_family_id == 0) {
+        Delete(key);
+      }
     }
     virtual void Delete(const Slice& key);
     // Continue is called by WriteBatch::Iterate. If it returns false,