Support to disable background compactions on a database.

Summary:
This option is needed for fast bulk uploads. The goal is to load
all the data into files in L0 without any interference from
background compactions.

Test Plan: make clean check

Reviewers: sheki

Reviewed By: sheki

CC: leveldb

Differential Revision: https://reviews.facebook.net/D6849

db/db_bench.cc

@@ -218,6 +218,9 @@ static int FLAGS_max_grandparent_overlap_factor;
 // Run read only benchmarks.
 static bool FLAGS_read_only = false;
 
+// Do not auto trigger compactions
+static bool FLAGS_disable_auto_compactions = false;
+
 extern bool useOsBuffer;
 extern bool useFsReadAhead;
 extern bool useMmapRead;
@@ -974,6 +977,7 @@ class Benchmark {
     options.table_cache_numshardbits = FLAGS_table_cache_numshardbits;
     options.max_grandparent_overlap_factor = 
       FLAGS_max_grandparent_overlap_factor;
+    options.disable_auto_compactions = FLAGS_disable_auto_compactions;
     Status s;
     if(FLAGS_read_only) {
       s = DB::OpenForReadOnly(options, FLAGS_db, &db_);
@@ -1424,6 +1428,9 @@ int main(int argc, char** argv) {
     } else if (sscanf(argv[i], "--max_grandparent_overlap_factor=%d%c",
                &n, &junk) == 1) {
       FLAGS_max_grandparent_overlap_factor = n;
+    } else if (sscanf(argv[i], "--disable_auto_compactions=%d%c", 
+               &n, &junk) == 1 && (n == 0 || n ==1)) {
+      FLAGS_disable_auto_compactions = n;
     } else {
       fprintf(stderr, "Invalid flag '%s'\n", argv[i]);
       exit(1);

db/db_impl.cc

@@ -1012,7 +1012,7 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress,
     }
   }
 
-  Compaction* c;
+  Compaction* c = NULL;
   bool is_manual = (manual_compaction_ != NULL) &&
                    (manual_compaction_->in_progress == false);
   InternalKey manual_end;
@@ -1031,7 +1031,7 @@ Status DBImpl::BackgroundCompaction(bool* madeProgress,
         (m->begin ? m->begin->DebugString().c_str() : "(begin)"),
         (m->end ? m->end->DebugString().c_str() : "(end)"),
         (m->done ? "(end)" : manual_end.DebugString().c_str()));
-  } else {
+  } else if (!options_.disable_auto_compactions) {
     c = versions_->PickCompaction();
   }
 

include/leveldb/options.h

@@ -330,6 +330,10 @@ struct Options {
   bool (*CompactionFilter)(void* compaction_filter_args, 
          int level, const Slice& key, 
          const Slice& existing_value, Slice** new_value);
+
+  // Disable automatic compactions. Manual compactions can still
+  // be issued on this database.
+  bool disable_auto_compactions;
 };
 
 // Options that control read operations

util/options.cc

@@ -51,7 +51,8 @@ Options::Options()
       no_block_cache(false),
       table_cache_numshardbits(4),
       compaction_filter_args(NULL),
-      CompactionFilter(NULL) {
+      CompactionFilter(NULL),
+      disable_auto_compactions(false) {
 }
 
 void
@@ -134,6 +135,8 @@ Options::Dump(
         compaction_filter_args);
     Log(log,"                       Options.CompactionFilter: %p",
         CompactionFilter);
+    Log(log,"               Options.disable_auto_compactions: %d",
+        disable_auto_compactions);
 }   // Options::Dump
 
 }  // namespace leveldb