Merge branch 'master' into performance

Conflicts:
	db/version_set.cc
	include/leveldb/options.h
	util/options.cc

include/leveldb/db.h

@@ -19,8 +19,8 @@ namespace leveldb {
 using std::unique_ptr;
 
 // Update Makefile if you change these
-static const int kMajorVersion = 1;
-static const int kMinorVersion = 5;
+static const int kMajorVersion = 2;
+static const int kMinorVersion = 0;
 
 struct Options;
 struct ReadOptions;
@@ -120,6 +120,11 @@ class DB {
                                        const std::vector<Slice>& keys,
                                        std::vector<std::string>* values) = 0;
 
+  // If the key definitely does not exist in the database, then this method
+  // returns false. Otherwise return true. This check is potentially
+  // lighter-weight than invoking DB::Get(). No IO is performed
+  virtual bool KeyMayExist(const Slice& key) = 0;
+
   // Return a heap-allocated iterator over the contents of the database.
   // The result of NewIterator() is initially invalid (caller must
   // call one of the Seek methods on the iterator before using it).

include/leveldb/options.h

@@ -422,17 +422,6 @@ struct Options {
   // Default: true
   bool allow_os_buffer;
 
-  // Reading a single block from a file can cause the OS/FS to start
-  // readaheads of other blocks from the file. Default: true
-  // Note: Deprecated
-  bool allow_readahead;
-
-  // The reads triggered by compaction allows data to be readahead
-  // by the OS/FS. This overrides the setting of 'allow_readahead'
-  // for compaction-reads. Default: true
-  // Note: Deprecated
-  bool allow_readahead_compactions;
-
   // Allow the OS to mmap file for reading sst tables. Default: false
   bool allow_mmap_reads;
 
@@ -487,6 +476,15 @@ struct Options {
 
   // The options needed to support Universal Style compactions
   CompactionOptionsUniversal compaction_options_universal;
+
+  // Use bloom-filter for deletes when this is true.
+  // db->Delete first calls KeyMayExist which checks memtable,immutable-memtable
+  // and bloom-filters to determine if the key does not exist in the database.
+  // If the key definitely does not exist, then the delete is a noop.KeyMayExist
+  // only incurs in-memory look up. This optimization avoids writing the delete
+  // to storage when appropriate.
+  // Default: false
+  bool deletes_check_filter_first;
 };
 
 // Options that control read operations

include/leveldb/statistics.h

@@ -58,7 +58,9 @@ enum Tickers {
   NUMBER_MULTIGET_KEYS_READ = 19,
   NUMBER_MULTIGET_BYTES_READ = 20,
 
-  TICKER_ENUM_MAX = 21
+  NUMBER_FILTERED_DELETES = 21,
+
+  TICKER_ENUM_MAX = 22
 };
 
 const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
@@ -82,7 +84,8 @@ const std::vector<std::pair<Tickers, std::string>> TickersNameMap = {
   { NO_ITERATORS, "rocksdb.num.iterators" },
   { NUMBER_MULTIGET_CALLS, "rocksdb.number.multiget.get" },
   { NUMBER_MULTIGET_KEYS_READ, "rocksdb.number.multiget.keys.read" },
-  { NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read" }
+  { NUMBER_MULTIGET_BYTES_READ, "rocksdb.number.multiget.bytes.read" },
+  { NUMBER_FILTERED_DELETES, "rocksdb.number.deletes.filtered" }
 };
 
 /**