added --rocksdb.num-uncompressed-levels

CHANGELOG

@@ -1,6 +1,8 @@
 devel
 -----
 
+* added --rocksdb.num-uncompressed-levels to adjust number of non-compressed levels
+
 * added checks for memory managment and warn (i. e. if hugepages are enabled)
 
 * set default SSL cipher suite string to "HIGH:!EXPORT:!aNULL@STRENGTH"

arangod/RocksDBEngine/RocksDBEngine.cpp

@@ -226,9 +226,11 @@ void RocksDBEngine::start() {
   // only compress levels >= 2
   _options.compression_per_level.resize(_options.num_levels);
   for (int level = 0; level < _options.num_levels; ++level) {
-    _options.compression_per_level[level] = ((level >= 2) ? rocksdb::kSnappyCompression : rocksdb::kNoCompression);
+    _options.compression_per_level[level] =
+        (((uint64_t) level >= opts->_numUncompressedLevels) ? rocksdb::kSnappyCompression
+                                                 : rocksdb::kNoCompression);
   }
-  
+
   // TODO: try out the effects of these options 
   // Number of files to trigger level-0 compaction. A value <0 means that
   // level-0 compaction will not be triggered by number of files at all.

lib/ApplicationFeatures/RocksDBOptionFeature.cpp

@@ -54,6 +54,7 @@ RocksDBOptionFeature::RocksDBOptionFeature(
       _minWriteBufferNumberToMerge(
           rocksDBDefaults.min_write_buffer_number_to_merge),
       _numLevels(rocksDBDefaults.num_levels),
+      _numUncompressedLevels(2),
       _maxBytesForLevelBase(rocksDBDefaults.max_bytes_for_level_base),
       _maxBytesForLevelMultiplier(
           rocksDBDefaults.max_bytes_for_level_multiplier),
@@ -128,6 +129,10 @@ void RocksDBOptionFeature::collectOptions(
                      "number of levels for the database",
                      new UInt64Parameter(&_numLevels));
 
+  options->addOption("--rocksdb.num-uncompressed-levels",
+                     "number of uncompressed levels for the database",
+                     new UInt64Parameter(&_numUncompressedLevels));
+
   options->addHiddenOption("--rocksdb.max-bytes-for-level-base",
                            "control maximum total data size for level-1",
                            new UInt64Parameter(&_maxBytesForLevelBase));

lib/ApplicationFeatures/RocksDBOptionFeature.h

@@ -52,6 +52,7 @@ class RocksDBOptionFeature final
   uint64_t _delayedWriteRate;
   uint64_t _minWriteBufferNumberToMerge;
   uint64_t _numLevels;
+  uint64_t _numUncompressedLevels;
   uint64_t _maxBytesForLevelBase;
   double _maxBytesForLevelMultiplier;
   uint64_t _baseBackgroundCompactions;