add an option to disable seek compaction

Summary:
as subject. This diff should be good for benchmarking.

will send another diff to make it better in the case the seek compaction is enable.
In that coming diff, will not count a seek if the bloomfilter filters.

Test Plan: build

Reviewers: dhruba, MarkCallaghan

Reviewed By: MarkCallaghan

Differential Revision: https://reviews.facebook.net/D5481

db/db_bench.cc

@@ -161,6 +161,9 @@ static int FLAGS_level0_slowdown_writes_trigger = 8;
 // setting is 9 gets for every 1 put.
 static int FLAGS_readwritepercent = 90;
 
+// Option to disable compation triggered by read.
+static int FLAGS_disable_seek_compaction = false;
+
 // Algorithm to use to compress the database
 static enum leveldb::CompressionType FLAGS_compression_type =
     leveldb::kSnappyCompression;
@@ -850,6 +853,7 @@ class Benchmark {
     options.level0_slowdown_writes_trigger =
       FLAGS_level0_slowdown_writes_trigger;
     options.compression = FLAGS_compression_type;
+    options.disable_seek_compaction = FLAGS_disable_seek_compaction;
     Status s = DB::Open(options, FLAGS_db, &db_);
     if (!s.ok()) {
       fprintf(stderr, "open error: %s\n", s.ToString().c_str());
@@ -1245,6 +1249,9 @@ int main(int argc, char** argv) {
       else {
         fprintf(stdout, "Cannot parse %s\n", argv[i]);
       }
+    } else if (sscanf(argv[i], "--disable_seek_compaction=%d%c", &n, &junk) == 1
+        && (n == 0 || n == 1)) {
+      FLAGS_disable_seek_compaction = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

db/version_set.cc

@@ -1380,7 +1380,7 @@ Compaction* VersionSet::PickCompaction() {
       // Wrap-around to the beginning of the key space
       c->inputs_[0].push_back(current_->files_[level][0]);
     }
-  } else if (seek_compaction) {
+  } else if (seek_compaction && !options_->disable_seek_compaction) {
     level = current_->file_to_compact_level_;
     c = new Compaction(level, MaxFileSizeForLevel(level),
 		MaxGrandParentOverlapBytes(level), NumberLevels());

include/leveldb/options.h

@@ -220,6 +220,12 @@ struct Options {
   // name's prefix.
   std::string db_log_dir;
 
+  // Disable compaction triggered by seek.
+  // With bloomfilter and fast storage, a miss on one level
+  // is very cheap if the file handle is cached in table cache
+  // (which is true if max_open_files is large).
+  bool disable_seek_compaction;
+
   // Create an Options object with default values for all fields.
   Options();
 

util/options.cc

@@ -39,7 +39,8 @@ Options::Options()
       disableDataSync(false),
       use_fsync(false),
       db_stats_log_interval(1800),
-      db_log_dir("") {
+      db_log_dir(""),
+      disable_seek_compaction(false) {
 }
 
 void
@@ -87,7 +88,8 @@ Options::Dump(
         max_grandparent_overlap_factor);
     Log(log,"         Options.db_log_dir: %s",
         db_log_dir.c_str());
-
+    Log(log,"         Options.disable_seek_compaction: %d",
+        disable_seek_compaction);
 }   // Options::Dump