Fix coverity issues in include/rocksdb

Summary:
include/rocksdb/metadata.h:
struct ColumnFamilyMetaData {

CID 1322804 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
2. uninit_member: Non-static class member file_count is not initialized in this constructor nor in any functions that it calls.

struct SstFileMetaData {
        2. uninit_member: Non-static class member size is not initialized in this constructor nor in any functions that it calls.
        4. uninit_member: Non-static class member smallest_seqno is not initialized in this constructor nor in any functions that it calls.
        6. uninit_member: Non-static class member largest_seqno is not initialized in this constructor nor in any functions that it calls.
        8. uninit_member: Non-static class member num_reads_sampled is not initialized in this constructor nor in any functions that it calls.

CID 1322807 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
10. uninit_member: Non-static class member being_compacted is not initialized in this constructor nor in any functions that it calls.

include/rocksdb/sst_file_writer.h:
struct ExternalSstFileInfo {
        2. uninit_member: Non-static class member sequence_number is not initialized in this constructor nor in any functions that it calls.
        4. uninit_member: Non-static class member file_size is not initialized in this constructor nor in any functions that it calls.
        6. uninit_member: Non-static class member num_entries is not initialized in this constructor nor in any functions that it calls.

CID 1351697 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
8. uninit_member: Non-static class member version is not initialized in this constructor nor in any functions that it calls.
 31  ExternalSstFileInfo() {}

include/rocksdb/utilities/transaction.h:
explicit Transaction(const TransactionDB* db) {}
        2. uninit_member: Non-static class member log_number_ is not initialized in this constructor nor in any functions that it calls.

CID 1396133 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
4. uninit_member: Non-static class member field txn_state_._M_i is not initialized in this constructor nor in any functions that it calls.
473  Transaction() {}
Closes https://github.com/facebook/rocksdb/pull/3100

Differential Revision: D6227651

Pulled By: sagar0

fbshipit-source-id: 5caa4a2cf9471d1f9c3c073f81473636e1f0aa14

include/rocksdb/metadata.h

@@ -20,7 +20,7 @@ struct SstFileMetaData;
 
 // The metadata that describes a column family.
 struct ColumnFamilyMetaData {
-  ColumnFamilyMetaData() : size(0), name("") {}
+  ColumnFamilyMetaData() : size(0), file_count(0), name("") {}
   ColumnFamilyMetaData(const std::string& _name, uint64_t _size,
                        const std::vector<LevelMetaData>&& _levels) :
       size(_size), name(_name), levels(_levels) {}
@@ -54,7 +54,16 @@ struct LevelMetaData {
 
 // The metadata that describes a SST file.
 struct SstFileMetaData {
-  SstFileMetaData() {}
+  SstFileMetaData()
+      : size(0),
+        name(""),
+        db_path(""),
+        smallest_seqno(0),
+        largest_seqno(0),
+        smallestkey(""),
+        largestkey(""),
+        num_reads_sampled(0),
+        being_compacted(false) {}
   SstFileMetaData(const std::string& _file_name, const std::string& _path,
                   uint64_t _size, SequenceNumber _smallest_seqno,
                   SequenceNumber _largest_seqno,

include/rocksdb/sst_file_writer.h

@@ -28,7 +28,15 @@ class Comparator;
 // ExternalSstFileInfo include information about sst files created
 // using SstFileWriter.
 struct ExternalSstFileInfo {
-  ExternalSstFileInfo() {}
+  ExternalSstFileInfo()
+      : file_path(""),
+        smallest_key(""),
+        largest_key(""),
+        sequence_number(0),
+        file_size(0),
+        num_entries(0),
+        version(0) {}
+
   ExternalSstFileInfo(const std::string& _file_path,
                       const std::string& _smallest_key,
                       const std::string& _largest_key,

include/rocksdb/utilities/transaction.h

@@ -470,7 +470,7 @@ class Transaction {
 
  protected:
   explicit Transaction(const TransactionDB* db) {}
-  Transaction() {}
+  Transaction() : log_number_(0), txn_state_(STARTED) {}
 
   // the log in which the prepared section for this txn resides
   // (for two phase commit)