Configurable compression in db_bench

Summary:
Made compression type and dictionary size configurable via environment
variables.

Depends on D52287.

Test Plan:
check these options are passed to the db.

  $ COMPRESSION_MAX_DICT_BYTES=65536 COMPRESSION_TYPE=LZ4 NUM_KEYS=10000000 DB_DIR=./tmp/ WAL_DIR=./tmp/ ./tools/benchmark.sh filluniquerandom
  ...
  $ grep Options.compression tmp/LOG
  2016/04/22-19:11:30.397829 7f5f263a2980          Options.compression: LZ4
  ...
  2016/04/22-19:11:30.397837 7f5f263a2980         Options.compression_opts.max_dict_bytes: 65536

Reviewers: IslamAbdelRahman, sdong

Reviewed By: sdong

Subscribers: andrewkr, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D57141

tools/benchmark.sh

@@ -49,6 +49,8 @@ mb_written_per_sec=${MB_WRITE_PER_SEC:-0}
 # Only for tests that do range scans
 num_nexts_per_seek=${NUM_NEXTS_PER_SEEK:-10}
 cache_size=${CACHE_SIZE:-$((1 * G))}
+compression_max_dict_bytes=${COMPRESSION_MAX_DICT_BYTES:-0}
+compression_type=${COMPRESSION_TYPE:-snappy}
 duration=${DURATION:-0}
 
 num_keys=${NUM_KEYS:-$((1 * G))}
@@ -68,9 +70,9 @@ const_params="
   --block_size=$block_size \
   --cache_size=$cache_size \
   --cache_numshardbits=6 \
-  --compression_type=snappy \
-  --min_level_to_compress=3 \
+  --compression_max_dict_bytes=$compression_max_dict_bytes \
   --compression_ratio=0.5 \
+  --compression_type=$compression_type \
   --level_compaction_dynamic_level_bytes=true \
   --bytes_per_sync=$((8 * M)) \
   --cache_index_and_filter_blocks=0 \

tools/db_bench_tool.cc

@@ -562,6 +562,10 @@ DEFINE_int32(compression_level, -1,
              "Compression level. For zlib this should be -1 for the "
              "default level, or between 0 and 9.");
 
+DEFINE_int32(compression_max_dict_bytes, 0,
+             "Maximum size of dictionary used to prime the compression "
+             "library.");
+
 static bool ValidateCompressionLevel(const char* flagname, int32_t value) {
   if (value < -1 || value > 9) {
     fprintf(stderr, "Invalid value for --%s: %d, must be between -1 and 9\n",
@@ -2556,6 +2560,7 @@ class Benchmark {
       FLAGS_level0_slowdown_writes_trigger;
     options.compression = FLAGS_compression_type_e;
     options.compression_opts.level = FLAGS_compression_level;
+    options.compression_opts.max_dict_bytes = FLAGS_compression_max_dict_bytes;
     options.WAL_ttl_seconds = FLAGS_wal_ttl_seconds;
     options.WAL_size_limit_MB = FLAGS_wal_size_limit_MB;
     options.max_total_wal_size = FLAGS_max_total_wal_size;