[RocksDB] Expose count for WriteBatch

Summary: As title. Exposed a Count function that returns the number of updates in a batch. Could be handy for replication sequence number check.

Test Plan: make check;

Reviewers: emayanke, sheki, dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D11523

db/write_batch.cc

@@ -45,6 +45,10 @@ void WriteBatch::Clear() {
   rep_.resize(kHeader);
 }
 
+int WriteBatch::Count() const {
+  return WriteBatchInternal::Count(this);
+}
+
 Status WriteBatch::Iterate(Handler* handler) const {
   Slice input(rep_);
   if (input.size() < kHeader) {

db/write_batch_test.cc

@@ -67,6 +67,7 @@ TEST(WriteBatchTest, Empty) {
   WriteBatch batch;
   ASSERT_EQ("", PrintContents(&batch));
   ASSERT_EQ(0, WriteBatchInternal::Count(&batch));
+  ASSERT_EQ(0, batch.Count());
 }
 
 TEST(WriteBatchTest, Multiple) {
@@ -81,6 +82,7 @@ TEST(WriteBatchTest, Multiple) {
             "Delete(box)@101"
             "Put(foo, bar)@100",
             PrintContents(&batch));
+  ASSERT_EQ(3, batch.Count());
 }
 
 TEST(WriteBatchTest, Corruption) {
@@ -103,16 +105,19 @@ TEST(WriteBatchTest, Append) {
   WriteBatchInternal::Append(&b1, &b2);
   ASSERT_EQ("",
             PrintContents(&b1));
+  ASSERT_EQ(0, b1.Count());
   b2.Put("a", "va");
   WriteBatchInternal::Append(&b1, &b2);
   ASSERT_EQ("Put(a, va)@200",
             PrintContents(&b1));
+  ASSERT_EQ(1, b1.Count());
   b2.Clear();
   b2.Put("b", "vb");
   WriteBatchInternal::Append(&b1, &b2);
   ASSERT_EQ("Put(a, va)@200"
             "Put(b, vb)@201",
             PrintContents(&b1));
+  ASSERT_EQ(2, b1.Count());
   b2.Delete("foo");
   WriteBatchInternal::Append(&b1, &b2);
   ASSERT_EQ("Put(a, va)@200"
@@ -120,6 +125,7 @@ TEST(WriteBatchTest, Append) {
             "Put(b, vb)@201"
             "Delete(foo)@203",
             PrintContents(&b1));
+  ASSERT_EQ(4, b1.Count());
 }
 
 }  // namespace leveldb

include/leveldb/write_batch.h

@@ -59,9 +59,12 @@ class WriteBatch {
   };
   Status Iterate(Handler* handler) const;
 
-  // Retrive the serialized version of this batch.
+  // Retrieve the serialized version of this batch.
   std::string Data() { return rep_; }
 
+  // Returns the number of updates in the batch
+  int Count() const;
+
   // Constructor with a serialized string object
   WriteBatch(std::string rep): rep_(rep) {}