Task AB#1310794: [LevelDB] Add option to disable seek compaction #4

db/c.cc

@@ -426,6 +426,10 @@ void leveldb_options_set_max_file_size(leveldb_options_t* opt, size_t s) {
   opt->rep.max_file_size = s;
 }
 
+void leveldb_options_set_disable_seek_autocompaction(leveldb_options_t* opt, uint8_t v) {
+  opt->rep.disable_seek_autocompaction = v;
+}
+
 void leveldb_options_set_compression(leveldb_options_t* opt, int t) {
   opt->rep.compression = static_cast<CompressionType>(t);
 }

db/version_set.cc

@@ -402,11 +402,13 @@ Status Version::Get(const ReadOptions& options, const LookupKey& k,
 bool Version::UpdateStats(const GetStats& stats) {
   FileMetaData* f = stats.seek_file;
   if (f != nullptr) {
-    f->allowed_seeks--;
-    if (f->allowed_seeks <= 0 && file_to_compact_ == nullptr) {
-      file_to_compact_ = f;
-      file_to_compact_level_ = stats.seek_file_level;
-      return true;
+    if (!vset_->options_->disable_seek_autocompaction) {
+      f->allowed_seeks--;
+      if (f->allowed_seeks <= 0 && file_to_compact_ == nullptr) {
+        file_to_compact_ = f;
+        file_to_compact_level_ = stats.seek_file_level;
+        return true;
+      }
     }
   }
   return false;
@@ -647,21 +649,23 @@ class VersionSet::Builder {
       FileMetaData* f = new FileMetaData(edit->new_files_[i].second);
       f->refs = 1;
 
-      // We arrange to automatically compact this file after
-      // a certain number of seeks.  Let's assume:
-      //   (1) One seek costs 10ms
-      //   (2) Writing or reading 1MB costs 10ms (100MB/s)
-      //   (3) A compaction of 1MB does 25MB of IO:
-      //         1MB read from this level
-      //         10-12MB read from next level (boundaries may be misaligned)
-      //         10-12MB written to next level
-      // This implies that 25 seeks cost the same as the compaction
-      // of 1MB of data.  I.e., one seek costs approximately the
-      // same as the compaction of 40KB of data.  We are a little
-      // conservative and allow approximately one seek for every 16KB
-      // of data before triggering a compaction.
-      f->allowed_seeks = static_cast<int>((f->file_size / 16384U));
-      if (f->allowed_seeks < 100) f->allowed_seeks = 100;
+      if (!vset_->options_->disable_seek_autocompaction) {
+        // We arrange to automatically compact this file after
+        // a certain number of seeks.  Let's assume:
+        //   (1) One seek costs 10ms
+        //   (2) Writing or reading 1MB costs 10ms (100MB/s)
+        //   (3) A compaction of 1MB does 25MB of IO:
+        //         1MB read from this level
+        //         10-12MB read from next level (boundaries may be misaligned)
+        //         10-12MB written to next level
+        // This implies that 25 seeks cost the same as the compaction
+        // of 1MB of data.  I.e., one seek costs approximately the
+        // same as the compaction of 40KB of data.  We are a little
+        // conservative and allow approximately one seek for every 16KB
+        // of data before triggering a compaction.
+        f->allowed_seeks = static_cast<int>((f->file_size / 16384U));
+        if (f->allowed_seeks < 100) f->allowed_seeks = 100;
+      }
 
       levels_[level].deleted_files.erase(f->number);
       levels_[level].added_files->insert(f);

include/leveldb/c.h

@@ -189,6 +189,8 @@ LEVELDB_EXPORT void leveldb_options_set_block_restart_interval(
     leveldb_options_t*, int);
 LEVELDB_EXPORT void leveldb_options_set_max_file_size(leveldb_options_t*,
                                                       size_t);
+LEVELDB_EXPORT void leveldb_options_set_disable_seek_autocompaction(leveldb_options_t*,
+                                                                    uint8_t);
 
 enum { leveldb_no_compression = 0, leveldb_snappy_compression = 1 };
 LEVELDB_EXPORT void leveldb_options_set_compression(leveldb_options_t*, int);

include/leveldb/options.h

@@ -145,6 +145,12 @@ struct LEVELDB_EXPORT Options {
   // Many applications will benefit from passing the result of
   // NewBloomFilterPolicy() here.
   const FilterPolicy* filter_policy = nullptr;
+
+  // Storage systems with low seek times (SSDs) may want to
+  // disable seek count triggered autocompaction altogether.
+  //
+  // Default: false
+  bool disable_seek_autocompaction = false;
 };
 
 // Options that control read operations