Change compaction_readahead_size default value to 2MB

db/db_compaction_test.cc

@@ -6025,23 +6025,18 @@ TEST_P(DBCompactionDirectIOTest, DirectIO) {
  options.use_direct_io_for_flush_and_compaction = GetParam();
  options.env = MockEnv::Create(Env::Default());
  Reopen(options);
- bool readahead = false;
  SyncPoint::GetInstance()->SetCallBack(
  "CompactionJob::OpenCompactionOutputFile", [&](void* arg) {
  bool* use_direct_writes = static_cast<bool*>(arg);
  ASSERT_EQ(*use_direct_writes,
  options.use_direct_io_for_flush_and_compaction);
  });
- if (options.use_direct_io_for_flush_and_compaction) {
- SyncPoint::GetInstance()->SetCallBack(
- "SanitizeOptions:direct_io", [&](void* /*arg*/) { readahead = true; });
- }
  SyncPoint::GetInstance()->EnableProcessing();
  CreateAndReopenWithCF({"pikachu"}, options);
  MakeTables(3, "p", "q", 1);
  ASSERT_EQ("1,1,1", FilesPerLevel(1));
  Compact(1, "p", "q");
- ASSERT_EQ(readahead, options.use_direct_reads);
+ ASSERT_EQ(false, options.use_direct_reads);
  ASSERT_EQ("0,0,1", FilesPerLevel(1));
  Destroy(options);
  delete options.env;

db/db_impl/db_impl_open.cc

@@ -143,13 +143,6 @@ DBOptions SanitizeOptions(const std::string& dbname, const DBOptions& src,
  result.wal_dir = result.wal_dir.substr(0, result.wal_dir.size() - 1);
  }
 
- if (result.compaction_readahead_size == 0) {
- if (result.use_direct_reads) {
- TEST_SYNC_POINT_CALLBACK("SanitizeOptions:direct_io", nullptr);
- }
- result.compaction_readahead_size = 1024 * 1024 * 2;
- }
-
  // Force flush on DB open if 2PC is enabled, since with 2PC we have no
  // guarantee that consecutive log files have consecutive sequence id, which
  // make recovery complicated.

db/db_options_test.cc

@@ -1034,30 +1034,37 @@ TEST_F(DBOptionsTest, SetFIFOCompactionOptions) {
 }
 
 TEST_F(DBOptionsTest, CompactionReadaheadSizeChange) {
- SpecialEnv env(env_);
- Options options;
- options.env = &env;
-
- options.compaction_readahead_size = 0;
- options.level0_file_num_compaction_trigger = 2;
- const std::string kValue(1024, 'v');
- Reopen(options);
+ for (bool use_direct_reads : {true, false}) {
+ SpecialEnv env(env_);
+ Options options;
+ options.env = &env;
+
+ options.use_direct_reads = use_direct_reads;
+ options.level0_file_num_compaction_trigger = 2;
+ const std::string kValue(1024, 'v');
+ Status s = TryReopen(options);
+ if (use_direct_reads && (s.IsNotSupported() || s.IsInvalidArgument())) {
+ continue;
+ } else {
+ ASSERT_OK(s);
+ }
 
- ASSERT_EQ(1024 * 1024 * 2,
- dbfull()->GetDBOptions().compaction_readahead_size);
- ASSERT_OK(dbfull()->SetDBOptions({{"compaction_readahead_size", "256"}}));
- ASSERT_EQ(256, dbfull()->GetDBOptions().compaction_readahead_size);
- for (int i = 0; i < 1024; i++) {
- ASSERT_OK(Put(Key(i), kValue));
- }
- ASSERT_OK(Flush());
- for (int i = 0; i < 1024 * 2; i++) {
- ASSERT_OK(Put(Key(i), kValue));
+ ASSERT_EQ(1024 * 1024 * 2,
+ dbfull()->GetDBOptions().compaction_readahead_size);
+ ASSERT_OK(dbfull()->SetDBOptions({{"compaction_readahead_size", "256"}}));
+ ASSERT_EQ(256, dbfull()->GetDBOptions().compaction_readahead_size);
+ for (int i = 0; i < 1024; i++) {
+ ASSERT_OK(Put(Key(i), kValue));
+ }
+ ASSERT_OK(Flush());
+ for (int i = 0; i < 1024 * 2; i++) {
+ ASSERT_OK(Put(Key(i), kValue));
+ }
+ ASSERT_OK(Flush());
+ ASSERT_OK(dbfull()->TEST_WaitForCompact());
+ ASSERT_EQ(256, env_->compaction_readahead_size_);
+ Close();
  }
- ASSERT_OK(Flush());
- ASSERT_OK(dbfull()->TEST_WaitForCompact());
- ASSERT_EQ(256, env_->compaction_readahead_size_);
- Close();
 }
 
 TEST_F(DBOptionsTest, FIFOTtlBackwardCompatible) {

include/rocksdb/options.h

@@ -955,10 +955,10 @@ struct DBOptions {
  // running RocksDB on spinning disks, you should set this to at least 2MB.
  // That way RocksDB's compaction is doing sequential instead of random reads.
  //
- // Default: 0
+ // Default: 2MB
  //
  // Dynamically changeable through SetDBOptions() API.
- size_t compaction_readahead_size = 0;
+ size_t compaction_readahead_size = 2 * 1024 * 1024;
 
  // This is a maximum buffer size that is used by WinMmapReadableFile in
  // unbuffered disk I/O mode. We need to maintain an aligned buffer for

unreleased_history/behavior_changes/buffered_io_compaction_readahead_size_zero.md

@@ -0,0 +1 @@
+Compaction read performance will regress when `Options::compaction_readahead_size` is explicitly set to 0

unreleased_history/public_api_changes/compaction_readahead_size_option_change.md

@@ -0,0 +1 @@
+`Options::compaction_readahead_size` 's default value is changed from 0 to 2MB.