db_bench: add IteratorCreationWhileWriting mode and allow prefix_seek

Summary: as title

Test Plan: ran it

Reviewers: igor, haobo, yhchiang

Reviewed By: igor

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17655

db/db_bench.cc

@@ -47,6 +47,8 @@ DEFINE_string(benchmarks,
               "overwrite,"
               "readrandom,"
               "readrandom,"
+              "newiterator,"
+              "newiteratorwhilewriting,"
               "readseq,"
               "readreverse,"
               "compact,"
@@ -1172,6 +1174,9 @@ class Benchmark {
         method = &Benchmark::ReadRandom;
       } else if (name == Slice("newiterator")) {
         method = &Benchmark::IteratorCreation;
+      } else if (name == Slice("newiteratorwhilewriting")) {
+        num_threads++;  // Add extra thread for writing
+        method = &Benchmark::IteratorCreationWhileWriting;
       } else if (name == Slice("seekrandom")) {
         method = &Benchmark::SeekRandom;
       } else if (name == Slice("readrandomsmall")) {
@@ -1864,6 +1869,7 @@ class Benchmark {
   void IteratorCreation(ThreadState* thread) {
     Duration duration(FLAGS_duration, reads_);
     ReadOptions options(FLAGS_verify_checksum, true);
+    options.prefix_seek = (FLAGS_prefix_size > 0);
     while (!duration.Done(1)) {
       Iterator* iter = db_->NewIterator(options);
       delete iter;
@@ -1871,6 +1877,14 @@ class Benchmark {
     }
   }
 
+  void IteratorCreationWhileWriting(ThreadState* thread) {
+    if (thread->tid > 0) {
+      IteratorCreation(thread);
+    } else {
+      BGWriter(thread);
+    }
+  }
+
   void SeekRandom(ThreadState* thread) {
     int64_t read = 0;
     int64_t found = 0;
@@ -1934,6 +1948,11 @@ class Benchmark {
     if (thread->tid > 0) {
       ReadRandom(thread);
     } else {
+      BGWriter(thread);
+    }
+  }
+
+  void BGWriter(ThreadState* thread) {
     // Special thread that keeps writing until other threads are done.
     RandomGenerator gen;
     double last = FLAGS_env->NowMicros();
@@ -1984,7 +2003,6 @@ class Benchmark {
       }
     }
   }
-  }
 
   // Given a key K and value V, this puts (K+"0", V), (K+"1", V), (K+"2", V)
   // in DB atomically i.e in a single batch. Also refer GetMany.