Add async_io read option in db_bench (#9735)

Summary:
Add async_io Read option in db_bench

Pull Request resolved: https://github.com/facebook/rocksdb/pull/9735

Test Plan:
./db_bench -use_existing_db=true
-db=/tmp/prefix_scan_prefetch_main -benchmarks="seekrandom" -key_size=32
-value_size=512 -num=5000000 -use_direct_reads=true -seek_nexts=327680
-duration=120 -ops_between_duration_checks=1 -async_io=1

Reviewed By: riversand963

Differential Revision: D35058482

Pulled By: akankshamahajan15

fbshipit-source-id: 1522b638c79f6d85bb7408c67f6ab76dbabeeee7

tools/db_bench_tool.cc

@@ -1124,6 +1124,10 @@ DEFINE_bool(rate_limit_auto_wal_flush, false,
             "false) after the user "
             "write operation");
 
+DEFINE_bool(async_io, false,
+            "When set true, RocksDB does asynchronous reads for internal auto "
+            "readahead prefetching.");
+
 static enum ROCKSDB_NAMESPACE::CompressionType StringToCompressionType(
     const char* ctype) {
   assert(ctype);
@@ -3120,6 +3124,7 @@ class Benchmark {
       read_options_.tailing = FLAGS_use_tailing_iterator;
       read_options_.readahead_size = FLAGS_readahead_size;
       read_options_.adaptive_readahead = FLAGS_adaptive_readahead;
+      read_options_.async_io = FLAGS_async_io;
 
       void (Benchmark::*method)(ThreadState*) = nullptr;
       void (Benchmark::*post_process_method)() = nullptr;
@@ -5402,6 +5407,8 @@ class Benchmark {
     }
 
     options.adaptive_readahead = FLAGS_adaptive_readahead;
+    options.async_io = FLAGS_async_io;
+
     Iterator* iter = db->NewIterator(options);
     int64_t i = 0;
     int64_t bytes = 0;
@@ -7317,6 +7324,7 @@ class Benchmark {
     DB* db = SelectDB(thread);
     ReadOptions ro;
     ro.adaptive_readahead = FLAGS_adaptive_readahead;
+    ro.async_io = FLAGS_async_io;
     ro.rate_limiter_priority =
         FLAGS_rate_limit_user_ops ? Env::IO_USER : Env::IO_TOTAL;
     ro.readahead_size = FLAGS_readahead_size;
@@ -7331,6 +7339,7 @@ class Benchmark {
     DB* db = SelectDB(thread);
     ReadOptions ro;
     ro.adaptive_readahead = FLAGS_adaptive_readahead;
+    ro.async_io = FLAGS_async_io;
     ro.rate_limiter_priority =
         FLAGS_rate_limit_user_ops ? Env::IO_USER : Env::IO_TOTAL;
     ro.readahead_size = FLAGS_readahead_size;