try to optimize rocksdb get

hope can improve performance

tools/build_rocksdb_ext.sh

@@ -0,0 +1,20 @@
+#!/bin/bash
+
+ROCKSDB_DIR=/usr/local/rocksdb
+
+if test -z "$TARGET_OS"; then
+    TARGET_OS=`uname -s`
+fi
+
+PLATFORM_SHARED_EXT="so"
+PLATFORM_SHARED_LDFLAGS="-shared -Wl,-soname -Wl,"
+PLATFORM_SHARED_CFLAGS="-fPIC"
+
+if [ "$TARGET_OS" = "Darwin" ]; then
+    PLATFORM_SHARED_EXT=dylib
+    PLATFORM_SHARED_LDFLAGS="-dynamiclib -install_name "
+fi
+
+SONAME=librocksdb_ext.$PLATFORM_SHARED_EXT
+
+g++ $PLATFORM_SHARED_LDFLAGS$SONAME $PLATFORM_SHARED_CFLAGS -std=c++0x -L$ROCKSDB_DIR/lib -lrocksdb -I/$ROCKSDB_DIR/include rocksdb_ext.cc -o $SONAME 

tools/rocksdb_ext.cc

@@ -0,0 +1,57 @@
+#include <rocksdb/c.h>
+#include <rocksdb/db.h>
+
+#include <string>
+
+using namespace rocksdb;
+
+extern "C" {
+
+static bool SaveError(char** errptr, const Status& s) {
+  assert(errptr != NULL);
+  if (s.ok()) {
+    return false;
+  } else if (*errptr == NULL) {
+    *errptr = strdup(s.ToString().c_str());
+  } else {
+    free(*errptr);
+    *errptr = strdup(s.ToString().c_str());
+  }
+  return true;
+}
+
+void* rocksdb_get_ext(
+    rocksdb_t* db,
+    const rocksdb_readoptions_t* options,
+    const char* key, size_t keylen,
+    char** valptr,
+    size_t* vallen,
+    char** errptr) {
+
+    std::string *tmp = new(std::string);
+
+    //very tricky, maybe changed with c++ rocksdb upgrade
+    Status s = (*(DB**)db)->Get(*(ReadOptions*)options, Slice(key, keylen), tmp);
+
+    if (s.ok()) {
+        *valptr = (char*)tmp->data();
+        *vallen = tmp->size();
+    } else {
+        delete(tmp);
+        tmp = NULL;
+        *valptr = NULL;
+        *vallen = 0;
+        if (!s.IsNotFound()) {
+            SaveError(errptr, s);
+        }
+    }
+    return tmp;
+}
+
+void rocksdb_get_free_ext(void* context) {
+    std::string* s = (std::string*)context;
+
+    delete(s);
+}
+
+}