update read me

leveldb/readme.md

@@ -6,3 +6,25 @@ simplify use leveldb in go
 
 + download leveldb and snappy source, uncompress and set source directory in build_deps.sh
 + . ./build_deps.sh
+
+# Performance
+
+for better performance, I change some leveldb configurations to build:
+
++ db/dbformat.h
+
+        // static const int kL0_SlowdownWritesTrigger = 8;
+        static const int kL0_SlowdownWritesTrigger = 16;
+
+        // static const int kL0_StopWritesTrigger = 12;
+        static const int kL0_StopWritesTrigger = 64;
+
++ db/version_set.cc
+
+        //static const int kTargetFileSize = 2 * 1048576;
+        static const int kTargetFileSize = 32 * 1048576;
+
+        //static const int64_t kMaxGrandParentOverlapBytes = 10 * kTargetFileSize;
+        static const int64_t kMaxGrandParentOverlapBytes = 20 * kTargetFileSize;
+
+