Feature for sampling and reporting compressibility (#4842)

Summary:
This is a feature to sample data-block compressibility and and report them as stats. 1 in N (tunable) blocks is sampled for compressibility using two algorithms:
1. lz4 or snappy for fast compression
2. zstd or zlib for slow but higher compression.

The stats are reported to the caller as raw-bytes and compressed-bytes. The block continues to be compressed for storage using the specified CompressionType.

The db_bench_tool how has a command line option for specifying the sampling rate. It's default value is 0 (no sampling). To test the overhead for a certain value, users can compare the performance of db_bench_tool, varying the sampling rate. It is unlikely to have a noticeable impact for high values like 20.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/4842

Differential Revision: D13629011

Pulled By: shobhitdayal

fbshipit-source-id: 14ca668bcab6499b2a1734edf848eb62a4f4fafa

HISTORY.md

@@ -10,6 +10,13 @@
 * Fix JEMALLOC_CXX_THROW macro missing from older Jemalloc versions, causing build failures on some platforms.
 
 
+## Unreleased
+### New Features
+* Added a feature to perform data-block sampling for compressibility, and report stats to user.
+### Public API Change
+### Bug fixes
+
+
 ## 6.0.0 (2/19/2019)
 ### New Features
 * Enabled checkpoint on readonly db (DBImplReadOnly).

db/builder.cc

@@ -47,8 +47,8 @@ TableBuilder* NewTableBuilder(
         int_tbl_prop_collector_factories,
     uint32_t column_family_id, const std::string& column_family_name,
     WritableFileWriter* file, const CompressionType compression_type,
-    const CompressionOptions& compression_opts, int level,
-    const bool skip_filters, const uint64_t creation_time,
+    uint64_t sample_for_compression, const CompressionOptions& compression_opts,
+    int level, const bool skip_filters, const uint64_t creation_time,
     const uint64_t oldest_key_time, const uint64_t target_file_size) {
   assert((column_family_id ==
           TablePropertiesCollectorFactory::Context::kUnknownColumnFamily) ==
@@ -56,9 +56,9 @@ TableBuilder* NewTableBuilder(
   return ioptions.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, internal_comparator,
                           int_tbl_prop_collector_factories, compression_type,
-                          compression_opts, skip_filters, column_family_name,
-                          level, creation_time, oldest_key_time,
-                          target_file_size),
+                          sample_for_compression, compression_opts,
+                          skip_filters, column_family_name, level,
+                          creation_time, oldest_key_time, target_file_size),
       column_family_id, file);
 }
 
@@ -75,11 +75,12 @@ Status BuildTable(
     std::vector<SequenceNumber> snapshots,
     SequenceNumber earliest_write_conflict_snapshot,
     SnapshotChecker* snapshot_checker, const CompressionType compression,
-    const CompressionOptions& compression_opts, bool paranoid_file_checks,
-    InternalStats* internal_stats, TableFileCreationReason reason,
-    EventLogger* event_logger, int job_id, const Env::IOPriority io_priority,
-    TableProperties* table_properties, int level, const uint64_t creation_time,
-    const uint64_t oldest_key_time, Env::WriteLifeTimeHint write_hint) {
+    uint64_t sample_for_compression, const CompressionOptions& compression_opts,
+    bool paranoid_file_checks, InternalStats* internal_stats,
+    TableFileCreationReason reason, EventLogger* event_logger, int job_id,
+    const Env::IOPriority io_priority, TableProperties* table_properties,
+    int level, const uint64_t creation_time, const uint64_t oldest_key_time,
+    Env::WriteLifeTimeHint write_hint) {
   assert((column_family_id ==
           TablePropertiesCollectorFactory::Context::kUnknownColumnFamily) ==
          column_family_name.empty());
@@ -133,8 +134,8 @@ Status BuildTable(
           ioptions, mutable_cf_options, internal_comparator,
           int_tbl_prop_collector_factories, column_family_id,
           column_family_name, file_writer.get(), compression,
-          compression_opts_for_flush, level, false /* skip_filters */,
-          creation_time, oldest_key_time);
+          sample_for_compression, compression_opts_for_flush, level,
+          false /* skip_filters */, creation_time, oldest_key_time);
     }
 
     MergeHelper merge(env, internal_comparator.user_comparator(),

db/builder.h

@@ -47,6 +47,7 @@ TableBuilder* NewTableBuilder(
         int_tbl_prop_collector_factories,
     uint32_t column_family_id, const std::string& column_family_name,
     WritableFileWriter* file, const CompressionType compression_type,
+    const uint64_t sample_for_compression,
     const CompressionOptions& compression_opts, int level,
     const bool skip_filters = false, const uint64_t creation_time = 0,
     const uint64_t oldest_key_time = 0, const uint64_t target_file_size = 0);
@@ -72,6 +73,7 @@ extern Status BuildTable(
     std::vector<SequenceNumber> snapshots,
     SequenceNumber earliest_write_conflict_snapshot,
     SnapshotChecker* snapshot_checker, const CompressionType compression,
+    const uint64_t sample_for_compression,
     const CompressionOptions& compression_opts, bool paranoid_file_checks,
     InternalStats* internal_stats, TableFileCreationReason reason,
     EventLogger* event_logger = nullptr, int job_id = 0,

db/compaction_job.cc

@@ -1499,6 +1499,7 @@ Status CompactionJob::OpenCompactionOutputFile(
       cfd->internal_comparator(), cfd->int_tbl_prop_collector_factories(),
       cfd->GetID(), cfd->GetName(), sub_compact->outfile.get(),
       sub_compact->compaction->output_compression(),
+      0 /*sample_for_compression */,
       sub_compact->compaction->output_compression_opts(),
       sub_compact->compaction->output_level(), skip_filters,
       output_file_creation_time, 0 /* oldest_key_time */,

db/db_impl_open.cc

@@ -1029,6 +1029,7 @@ Status DBImpl::WriteLevel0TableForRecovery(int job_id, ColumnFamilyData* cfd,
           cfd->int_tbl_prop_collector_factories(), cfd->GetID(), cfd->GetName(),
           snapshot_seqs, earliest_write_conflict_snapshot, snapshot_checker,
           GetCompressionFlush(*cfd->ioptions(), mutable_cf_options),
+          mutable_cf_options.sample_for_compression,
           cfd->ioptions()->compression_opts, paranoid_file_checks,
           cfd->internal_stats(), TableFileCreationReason::kRecovery,
           &event_logger_, job_id, Env::IO_HIGH, nullptr /* table_properties */,

db/flush_job.cc

@@ -372,7 +372,8 @@ Status FlushJob::WriteLevel0Table() {
           cfd_->int_tbl_prop_collector_factories(), cfd_->GetID(),
           cfd_->GetName(), existing_snapshots_,
           earliest_write_conflict_snapshot_, snapshot_checker_,
-          output_compression_, cfd_->ioptions()->compression_opts,
+          output_compression_, mutable_cf_options_.sample_for_compression,
+          cfd_->ioptions()->compression_opts,
           mutable_cf_options_.paranoid_file_checks, cfd_->internal_stats(),
           TableFileCreationReason::kFlush, event_logger_, job_context_->job_id,
           Env::IO_HIGH, &table_properties_, 0 /* level */, current_time,

db/repair.cc

@@ -430,10 +430,11 @@ class Repairer {
           &meta, cfd->internal_comparator(),
           cfd->int_tbl_prop_collector_factories(), cfd->GetID(), cfd->GetName(),
           {}, kMaxSequenceNumber, snapshot_checker, kNoCompression,
-          CompressionOptions(), false, nullptr /* internal_stats */,
-          TableFileCreationReason::kRecovery, nullptr /* event_logger */,
-          0 /* job_id */, Env::IO_HIGH, nullptr /* table_properties */,
-          -1 /* level */, current_time, write_hint);
+          0 /* sample_for_compression */, CompressionOptions(), false,
+          nullptr /* internal_stats */, TableFileCreationReason::kRecovery,
+          nullptr /* event_logger */, 0 /* job_id */, Env::IO_HIGH,
+          nullptr /* table_properties */, -1 /* level */, current_time,
+          write_hint);
       ROCKS_LOG_INFO(db_options_.info_log,
                      "Log #%" PRIu64 ": %d ops saved to Table #%" PRIu64 " %s",
                      log, counter, meta.fd.GetNumber(),

db/table_properties_collector.cc

@@ -41,6 +41,13 @@ Status UserKeyTablePropertiesCollector::InternalAdd(const Slice& key,
                                 ikey.sequence, file_size);
 }
 
+void UserKeyTablePropertiesCollector::BlockAdd(
+    uint64_t bLockRawBytes, uint64_t blockCompressedBytesFast,
+    uint64_t blockCompressedBytesSlow) {
+  return collector_->BlockAdd(bLockRawBytes, blockCompressedBytesFast,
+                              blockCompressedBytesSlow);
+}
+
 Status UserKeyTablePropertiesCollector::Finish(
     UserCollectedProperties* properties) {
   return collector_->Finish(properties);

db/table_properties_collector.h

@@ -27,6 +27,10 @@ class IntTblPropCollector {
   virtual Status InternalAdd(const Slice& key, const Slice& value,
                              uint64_t file_size) = 0;
 
+  virtual void BlockAdd(uint64_t blockRawBytes,
+                        uint64_t blockCompressedBytesFast,
+                        uint64_t blockCompressedBytesSlow) = 0;
+
   virtual UserCollectedProperties GetReadableProperties() const = 0;
 
   virtual bool NeedCompact() const { return false; }
@@ -60,6 +64,10 @@ class UserKeyTablePropertiesCollector : public IntTblPropCollector {
   virtual Status InternalAdd(const Slice& key, const Slice& value,
                              uint64_t file_size) override;
 
+  virtual void BlockAdd(uint64_t blockRawBytes,
+                        uint64_t blockCompressedBytesFast,
+                        uint64_t blockCompressedBytesSlow) override;
+
   virtual Status Finish(UserCollectedProperties* properties) override;
 
   virtual const char* Name() const override { return collector_->Name(); }

db/table_properties_collector_test.cc

@@ -52,7 +52,8 @@ void MakeBuilder(const Options& options, const ImmutableCFOptions& ioptions,
   builder->reset(NewTableBuilder(
       ioptions, moptions, internal_comparator, int_tbl_prop_collector_factories,
       kTestColumnFamilyId, kTestColumnFamilyName, writable->get(),
-      options.compression, options.compression_opts, unknown_level));
+      options.compression, options.sample_for_compression,
+      options.compression_opts, unknown_level));
 }
 }  // namespace
 
@@ -172,6 +173,13 @@ class RegularKeysStartWithAInternal : public IntTblPropCollector {
     return Status::OK();
   }
 
+  void BlockAdd(uint64_t /* blockRawBytes */,
+                uint64_t /* blockCompressedBytesFast */,
+                uint64_t /* blockCompressedBytesSlow */) override {
+    // Nothing to do.
+    return;
+  }
+
   UserCollectedProperties GetReadableProperties() const override {
     return UserCollectedProperties{};
   }

include/rocksdb/advanced_options.h

@@ -644,6 +644,12 @@ struct AdvancedColumnFamilyOptions {
   // Dynamically changeable through SetOptions() API
   uint64_t ttl = 0;
 
+  // If this option is set then 1 in N blocks are compressed
+  // using a fast (lz4) and slow (zstd) compression algorithm.
+  // The compressibility is reported as stats and the stored
+  // data is left uncompressed (unless compression is also requested).
+  uint64_t sample_for_compression = 0;
+
   // Create ColumnFamilyOptions with default values for all fields
   AdvancedColumnFamilyOptions();
   // Create ColumnFamilyOptions from Options

include/rocksdb/table_properties.h

@@ -92,6 +92,14 @@ class TablePropertiesCollector {
     return Add(key, value);
   }
 
+  // Called after each new block is cut
+  virtual void BlockAdd(uint64_t /* blockRawBytes */,
+                        uint64_t /* blockCompressedBytesFast */,
+                        uint64_t /* blockCompressedBytesSlow */) {
+    // Nothing to do here. Callback registers can override.
+    return;
+  }
+
   // Finish() will be called when a table has already been built and is ready
   // for writing the properties block.
   // @params properties  User will add their collected statistics to

options/cf_options.h

@@ -159,7 +159,8 @@ struct MutableCFOptions {
             options.max_sequential_skip_in_iterations),
         paranoid_file_checks(options.paranoid_file_checks),
         report_bg_io_stats(options.report_bg_io_stats),
-        compression(options.compression) {
+        compression(options.compression),
+        sample_for_compression(options.sample_for_compression) {
     RefreshDerivedOptions(options.num_levels, options.compaction_style);
   }
 
@@ -189,7 +190,8 @@ struct MutableCFOptions {
         max_sequential_skip_in_iterations(0),
         paranoid_file_checks(false),
         report_bg_io_stats(false),
-        compression(Snappy_Supported() ? kSnappyCompression : kNoCompression) {}
+        compression(Snappy_Supported() ? kSnappyCompression : kNoCompression),
+        sample_for_compression(0) {}
 
   explicit MutableCFOptions(const Options& options);
 
@@ -243,6 +245,7 @@ struct MutableCFOptions {
   bool paranoid_file_checks;
   bool report_bg_io_stats;
   CompressionType compression;
+  uint64_t sample_for_compression;
 
   // Derived options
   // Per-level target file size.

options/options.cc

@@ -87,7 +87,8 @@ AdvancedColumnFamilyOptions::AdvancedColumnFamilyOptions(const Options& options)
       paranoid_file_checks(options.paranoid_file_checks),
       force_consistency_checks(options.force_consistency_checks),
       report_bg_io_stats(options.report_bg_io_stats),
-      ttl(options.ttl) {
+      ttl(options.ttl),
+      sample_for_compression(options.sample_for_compression) {
   assert(memtable_factory.get() != nullptr);
   if (max_bytes_for_level_multiplier_additional.size() <
       static_cast<unsigned int>(num_levels)) {

options/options_helper.cc

@@ -193,6 +193,7 @@ ColumnFamilyOptions BuildColumnFamilyOptions(
   cf_opts.paranoid_file_checks = mutable_cf_options.paranoid_file_checks;
   cf_opts.report_bg_io_stats = mutable_cf_options.report_bg_io_stats;
   cf_opts.compression = mutable_cf_options.compression;
+  cf_opts.sample_for_compression = mutable_cf_options.sample_for_compression;
 
   cf_opts.table_factory = options.table_factory;
   // TODO(yhchiang): find some way to handle the following derived options
@@ -1927,7 +1928,11 @@ std::unordered_map<std::string, OptionTypeInfo>
         {"ttl",
          {offset_of(&ColumnFamilyOptions::ttl), OptionType::kUInt64T,
           OptionVerificationType::kNormal, true,
-          offsetof(struct MutableCFOptions, ttl)}}};
+          offsetof(struct MutableCFOptions, ttl)}},
+        {"sample_for_compression",
+         {offset_of(&ColumnFamilyOptions::sample_for_compression),
+          OptionType::kUInt64T, OptionVerificationType::kNormal, true,
+          offsetof(struct MutableCFOptions, sample_for_compression)}}};
 
 std::unordered_map<std::string, OptionTypeInfo>
     OptionsHelper::fifo_compaction_options_type_info = {

options/options_settable_test.cc

@@ -451,6 +451,7 @@ TEST_F(OptionsSettableTest, ColumnFamilyOptionsAllFieldsSettable) {
       "disable_auto_compactions=false;"
       "report_bg_io_stats=true;"
       "ttl=60;"
+      "sample_for_compression=0;"
       "compaction_options_fifo={max_table_files_size=3;allow_"
       "compaction=false;};",
       new_options));

table/block_based_table_builder.cc

@@ -101,83 +101,105 @@ bool GoodCompressionRatio(size_t compressed_size, size_t raw_size) {
   return compressed_size < raw_size - (raw_size / 8u);
 }
 
-}  // namespace
-
-// format_version is the block format as defined in include/rocksdb/table.h
-Slice CompressBlock(const Slice& raw, const CompressionInfo& compression_info,
-                    CompressionType* type, uint32_t format_version,
+bool CompressBlockInternal(const Slice& raw,
+                           const CompressionInfo& compression_info,
+                           uint32_t format_version,
                            std::string* compressed_output) {
-  *type = compression_info.type();
-  if (compression_info.type() == kNoCompression) {
-    return raw;
-  }
-
   // Will return compressed block contents if (1) the compression method is
   // supported in this platform and (2) the compression rate is "good enough".
   switch (compression_info.type()) {
     case kSnappyCompression:
-      if (Snappy_Compress(compression_info, raw.data(), raw.size(),
-                          compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;  // fall back to no compression.
+      return Snappy_Compress(compression_info, raw.data(), raw.size(),
+                             compressed_output);
     case kZlibCompression:
-      if (Zlib_Compress(
+      return Zlib_Compress(
           compression_info,
           GetCompressFormatForVersion(kZlibCompression, format_version),
-              raw.data(), raw.size(), compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;  // fall back to no compression.
+          raw.data(), raw.size(), compressed_output);
     case kBZip2Compression:
-      if (BZip2_Compress(
+      return BZip2_Compress(
           compression_info,
           GetCompressFormatForVersion(kBZip2Compression, format_version),
-              raw.data(), raw.size(), compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;  // fall back to no compression.
+          raw.data(), raw.size(), compressed_output);
     case kLZ4Compression:
-      if (LZ4_Compress(
+      return LZ4_Compress(
           compression_info,
           GetCompressFormatForVersion(kLZ4Compression, format_version),
-              raw.data(), raw.size(), compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;  // fall back to no compression.
+          raw.data(), raw.size(), compressed_output);
     case kLZ4HCCompression:
-      if (LZ4HC_Compress(
+      return LZ4HC_Compress(
           compression_info,
           GetCompressFormatForVersion(kLZ4HCCompression, format_version),
-              raw.data(), raw.size(), compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;     // fall back to no compression.
+          raw.data(), raw.size(), compressed_output);
     case kXpressCompression:
-      if (XPRESS_Compress(raw.data(), raw.size(),
-          compressed_output) &&
-          GoodCompressionRatio(compressed_output->size(), raw.size())) {
-        return *compressed_output;
-      }
-      break;
+      return XPRESS_Compress(raw.data(), raw.size(), compressed_output);
     case kZSTD:
     case kZSTDNotFinalCompression:
-      if (ZSTD_Compress(compression_info, raw.data(), raw.size(),
-                        compressed_output) &&
+      return ZSTD_Compress(compression_info, raw.data(), raw.size(),
+                           compressed_output);
+    default:
+      // Do not recognize this compression type
+      return false;
+  }
+}
+
+}  // namespace
+
+// format_version is the block format as defined in include/rocksdb/table.h
+Slice CompressBlock(const Slice& raw, const CompressionInfo& info,
+                    CompressionType* type, uint32_t format_version,
+                    bool do_sample, std::string* compressed_output,
+                    std::string* sampled_output_fast,
+                    std::string* sampled_output_slow) {
+  *type = info.type();
+
+  if (info.type() == kNoCompression && !info.SampleForCompression()) {
+    return raw;
+  }
+
+  // If requested, we sample one in every N block with a
+  // fast and slow compression algorithm and report the stats.
+  // The users can use these stats to decide if it is worthwhile
+  // enabling compression and they also get a hint about which
+  // compression algorithm wil be beneficial.
+  if (do_sample && info.SampleForCompression() &&
+      Random::GetTLSInstance()->OneIn((int)info.SampleForCompression()) &&
+      sampled_output_fast && sampled_output_slow) {
+    // Sampling with a fast compression algorithm
+    if (LZ4_Supported() || Snappy_Supported()) {
+      CompressionType c =
+          LZ4_Supported() ? kLZ4Compression : kSnappyCompression;
+      CompressionContext context(c);
+      CompressionOptions options;
+      CompressionInfo info_tmp(options, context,
+                               CompressionDict::GetEmptyDict(), c,
+                               info.SampleForCompression());
+
+      CompressBlockInternal(raw, info_tmp, format_version, sampled_output_fast);
+    }
+
+    // Sampling with a slow but high-compression algorithm
+    if (ZSTD_Supported() || Zlib_Supported()) {
+      CompressionType c = ZSTD_Supported() ? kZSTD : kZlibCompression;
+      CompressionContext context(c);
+      CompressionOptions options;
+      CompressionInfo info_tmp(options, context,
+                               CompressionDict::GetEmptyDict(), c,
+                               info.SampleForCompression());
+      CompressBlockInternal(raw, info_tmp, format_version, sampled_output_slow);
+    }
+  }
+
+  // Actually compress the data
+  if (*type != kNoCompression) {
+    if (CompressBlockInternal(raw, info, format_version, compressed_output) &&
         GoodCompressionRatio(compressed_output->size(), raw.size())) {
       return *compressed_output;
     }
-      break;     // fall back to no compression.
-    default: {}  // Do not recognize this compression type
   }
 
-  // Compression method is not supported, or not good compression ratio, so just
-  // fall back to uncompressed form.
+  // Compression method is not supported, or not good
+  // compression ratio, so just fall back to uncompressed form.
   *type = kNoCompression;
   return raw;
 }
@@ -217,6 +239,14 @@ class BlockBasedTableBuilder::BlockBasedTablePropertiesCollector
     return Status::OK();
   }
 
+  virtual void BlockAdd(uint64_t /* blockRawBytes */,
+                        uint64_t /* blockCompressedBytesFast */,
+                        uint64_t /* blockCompressedBytesSlow */) override {
+    // Intentionally left blank. No interest in collecting stats for
+    // blocks.
+    return;
+  }
+
   Status Finish(UserCollectedProperties* properties) override {
     std::string val;
     PutFixed32(&val, static_cast<uint32_t>(index_type_));
@@ -269,6 +299,7 @@ struct BlockBasedTableBuilder::Rep {
 
   std::string last_key;
   CompressionType compression_type;
+  uint64_t sample_for_compression;
   CompressionOptions compression_opts;
   std::unique_ptr<CompressionDict> compression_dict;
   CompressionContext compression_ctx;
@@ -328,6 +359,7 @@ struct BlockBasedTableBuilder::Rep {
           int_tbl_prop_collector_factories,
       uint32_t _column_family_id, WritableFileWriter* f,
       const CompressionType _compression_type,
+      const uint64_t _sample_for_compression,
       const CompressionOptions& _compression_opts, const bool skip_filters,
       const std::string& _column_family_name, const uint64_t _creation_time,
       const uint64_t _oldest_key_time, const uint64_t _target_file_size)
@@ -350,6 +382,7 @@ struct BlockBasedTableBuilder::Rep {
         range_del_block(1 /* block_restart_interval */),
         internal_prefix_transform(_moptions.prefix_extractor.get()),
         compression_type(_compression_type),
+        sample_for_compression(_sample_for_compression),
         compression_opts(_compression_opts),
         compression_dict(),
         compression_ctx(_compression_type),
@@ -415,6 +448,7 @@ BlockBasedTableBuilder::BlockBasedTableBuilder(
         int_tbl_prop_collector_factories,
     uint32_t column_family_id, WritableFileWriter* file,
     const CompressionType compression_type,
+    const uint64_t sample_for_compression,
     const CompressionOptions& compression_opts, const bool skip_filters,
     const std::string& column_family_name, const uint64_t creation_time,
     const uint64_t oldest_key_time, const uint64_t target_file_size) {
@@ -430,11 +464,11 @@ BlockBasedTableBuilder::BlockBasedTableBuilder(
     sanitized_table_options.format_version = 1;
   }
 
-  rep_ = new Rep(ioptions, moptions, sanitized_table_options,
-                 internal_comparator, int_tbl_prop_collector_factories,
-                 column_family_id, file, compression_type, compression_opts,
-                 skip_filters, column_family_name, creation_time,
-                 oldest_key_time, target_file_size);
+  rep_ = new Rep(
+      ioptions, moptions, sanitized_table_options, internal_comparator,
+      int_tbl_prop_collector_factories, column_family_id, file,
+      compression_type, sample_for_compression, compression_opts, skip_filters,
+      column_family_name, creation_time, oldest_key_time, target_file_size);
 
   if (rep_->filter_builder != nullptr) {
     rep_->filter_builder->StartBlock(0);
@@ -558,6 +592,7 @@ void BlockBasedTableBuilder::WriteBlock(const Slice& raw_block_contents,
   Rep* r = rep_;
 
   auto type = r->compression_type;
+  uint64_t sample_for_compression = r->sample_for_compression;
   Slice block_contents;
   bool abort_compression = false;
 
@@ -581,10 +616,20 @@ void BlockBasedTableBuilder::WriteBlock(const Slice& raw_block_contents,
     }
     assert(compression_dict != nullptr);
     CompressionInfo compression_info(r->compression_opts, r->compression_ctx,
-                                     *compression_dict, r->compression_type);
-    block_contents =
-        CompressBlock(raw_block_contents, compression_info, &type,
-                      r->table_options.format_version, &r->compressed_output);
+                                     *compression_dict, type,
+                                     sample_for_compression);
+
+    std::string sampled_output_fast;
+    std::string sampled_output_slow;
+    block_contents = CompressBlock(
+        raw_block_contents, compression_info, &type,
+        r->table_options.format_version, is_data_block /* do_sample */,
+        &r->compressed_output, &sampled_output_fast, &sampled_output_slow);
+
+    // notify collectors on block add
+    NotifyCollectTableCollectorsOnBlockAdd(
+        r->table_properties_collectors, raw_block_contents.size(),
+        sampled_output_fast.size(), sampled_output_slow.size());
 
     // Some of the compression algorithms are known to be unreliable. If
     // the verify_compression flag is set then try to de-compress the

table/block_based_table_builder.h

@@ -45,6 +45,7 @@ class BlockBasedTableBuilder : public TableBuilder {
           int_tbl_prop_collector_factories,
       uint32_t column_family_id, WritableFileWriter* file,
       const CompressionType compression_type,
+      const uint64_t sample_for_compression,
       const CompressionOptions& compression_opts, const bool skip_filters,
       const std::string& column_family_name, const uint64_t creation_time = 0,
       const uint64_t oldest_key_time = 0, const uint64_t target_file_size = 0);
@@ -137,6 +138,8 @@ class BlockBasedTableBuilder : public TableBuilder {
 
 Slice CompressBlock(const Slice& raw, const CompressionInfo& info,
                     CompressionType* type, uint32_t format_version,
-                    std::string* compressed_output);
+                    bool do_sample, std::string* compressed_output,
+                    std::string* sampled_output_fast,
+                    std::string* sampled_output_slow);
 
 }  // namespace rocksdb

table/block_based_table_factory.cc

@@ -214,6 +214,7 @@ TableBuilder* BlockBasedTableFactory::NewTableBuilder(
       table_options_, table_builder_options.internal_comparator,
       table_builder_options.int_tbl_prop_collector_factories, column_family_id,
       file, table_builder_options.compression_type,
+      table_builder_options.sample_for_compression,
       table_builder_options.compression_opts,
       table_builder_options.skip_filters,
       table_builder_options.column_family_name,

table/data_block_hash_index_test.cc

@@ -558,8 +558,9 @@ void TestBoundary(InternalKey& ik1, std::string& v1, InternalKey& ik2,
   builder.reset(ioptions.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, internal_comparator,
                           &int_tbl_prop_collector_factories,
-                          options.compression, CompressionOptions(),
-                          false /* skip_filters */, column_family_name, level_),
+                          options.compression, options.sample_for_compression,
+                          CompressionOptions(), false /* skip_filters */,
+                          column_family_name, level_),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 

table/meta_blocks.cc

@@ -151,6 +151,16 @@ bool NotifyCollectTableCollectorsOnAdd(
   return all_succeeded;
 }
 
+void NotifyCollectTableCollectorsOnBlockAdd(
+    const std::vector<std::unique_ptr<IntTblPropCollector>>& collectors,
+    const uint64_t blockRawBytes, const uint64_t blockCompressedBytesFast,
+    const uint64_t blockCompressedBytesSlow) {
+  for (auto& collector : collectors) {
+    collector->BlockAdd(blockRawBytes, blockCompressedBytesFast,
+                        blockCompressedBytesSlow);
+  }
+}
+
 bool NotifyCollectTableCollectorsOnFinish(
     const std::vector<std::unique_ptr<IntTblPropCollector>>& collectors,
     Logger* info_log, PropertyBlockBuilder* builder) {

table/meta_blocks.h

@@ -83,6 +83,11 @@ bool NotifyCollectTableCollectorsOnAdd(
     const std::vector<std::unique_ptr<IntTblPropCollector>>& collectors,
     Logger* info_log);
 
+void NotifyCollectTableCollectorsOnBlockAdd(
+    const std::vector<std::unique_ptr<IntTblPropCollector>>& collectors,
+    uint64_t blockRawBytes, uint64_t blockCompressedBytesFast,
+    uint64_t blockCompressedBytesSlow);
+
 // NotifyCollectTableCollectorsOnAdd() triggers the `Finish` event for all
 // property collectors. The collected properties will be added to `builder`.
 bool NotifyCollectTableCollectorsOnFinish(

table/sst_file_writer.cc

@@ -202,6 +202,8 @@ Status SstFileWriter::Open(const std::string& file_path) {
     compression_type = r->mutable_cf_options.compression;
     compression_opts = r->ioptions.compression_opts;
   }
+  uint64_t sample_for_compression =
+      r->mutable_cf_options.sample_for_compression;
 
   std::vector<std::unique_ptr<IntTblPropCollectorFactory>>
       int_tbl_prop_collector_factories;
@@ -234,8 +236,9 @@ Status SstFileWriter::Open(const std::string& file_path) {
 
   TableBuilderOptions table_builder_options(
       r->ioptions, r->mutable_cf_options, r->internal_comparator,
-      &int_tbl_prop_collector_factories, compression_type, compression_opts,
-      r->skip_filters, r->column_family_name, unknown_level);
+      &int_tbl_prop_collector_factories, compression_type,
+      sample_for_compression, compression_opts, r->skip_filters,
+      r->column_family_name, unknown_level);
   r->file_writer.reset(new WritableFileWriter(
       std::move(sst_file), file_path, r->env_options, r->ioptions.env,
       nullptr /* stats */, r->ioptions.listeners));

table/sst_file_writer_collectors.h

@@ -33,6 +33,14 @@ class SstFileWriterPropertiesCollector : public IntTblPropCollector {
     return Status::OK();
   }
 
+  virtual void BlockAdd(uint64_t /* blockRawBytes */,
+                        uint64_t /* blockCompressedBytesFast */,
+                        uint64_t /* blockCompressedBytesSlow */) override {
+    // Intentionally left blank. No interest in collecting stats for
+    // blocks.
+    return;
+  }
+
   virtual Status Finish(UserCollectedProperties* properties) override {
     // File version
     std::string version_val;

table/table_builder.h

@@ -73,7 +73,7 @@ struct TableBuilderOptions {
       const InternalKeyComparator& _internal_comparator,
       const std::vector<std::unique_ptr<IntTblPropCollectorFactory>>*
           _int_tbl_prop_collector_factories,
-      CompressionType _compression_type,
+      CompressionType _compression_type, uint64_t _sample_for_compression,
       const CompressionOptions& _compression_opts, bool _skip_filters,
       const std::string& _column_family_name, int _level,
       const uint64_t _creation_time = 0, const int64_t _oldest_key_time = 0,
@@ -83,6 +83,7 @@ struct TableBuilderOptions {
         internal_comparator(_internal_comparator),
         int_tbl_prop_collector_factories(_int_tbl_prop_collector_factories),
         compression_type(_compression_type),
+        sample_for_compression(_sample_for_compression),
         compression_opts(_compression_opts),
         skip_filters(_skip_filters),
         column_family_name(_column_family_name),
@@ -96,6 +97,7 @@ struct TableBuilderOptions {
   const std::vector<std::unique_ptr<IntTblPropCollectorFactory>>*
       int_tbl_prop_collector_factories;
   CompressionType compression_type;
+  uint64_t sample_for_compression;
   const CompressionOptions& compression_opts;
   bool skip_filters;  // only used by BlockBasedTableBuilder
   const std::string& column_family_name;

table/table_reader_bench.cc

@@ -100,8 +100,9 @@ void TableReaderBenchmark(Options& opts, EnvOptions& env_options,
     tb = opts.table_factory->NewTableBuilder(
         TableBuilderOptions(
             ioptions, moptions, ikc, &int_tbl_prop_collector_factories,
-            CompressionType::kNoCompression, CompressionOptions(),
-            false /* skip_filters */, kDefaultColumnFamilyName, unknown_level),
+            CompressionType::kNoCompression, 0 /* sample_for_compression */,
+            CompressionOptions(), false /* skip_filters */,
+            kDefaultColumnFamilyName, unknown_level),
         0 /* column_family_id */, file_writer.get());
   } else {
     s = DB::Open(opts, dbname, &db);

table/table_test.cc

@@ -328,9 +328,9 @@ class TableConstructor: public Constructor {
     builder.reset(ioptions.table_factory->NewTableBuilder(
         TableBuilderOptions(ioptions, moptions, internal_comparator,
                             &int_tbl_prop_collector_factories,
-                            options.compression, CompressionOptions(),
-                            false /* skip_filters */, column_family_name,
-                            level_),
+                            options.compression, options.sample_for_compression,
+                            CompressionOptions(), false /* skip_filters */,
+                            column_family_name, level_),
         TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
         file_writer_.get()));
 
@@ -2627,10 +2627,10 @@ TEST_F(PlainTableTest, BasicPlainTableProperties) {
   std::string column_family_name;
   int unknown_level = -1;
   std::unique_ptr<TableBuilder> builder(factory.NewTableBuilder(
-      TableBuilderOptions(ioptions, moptions, ikc,
-                          &int_tbl_prop_collector_factories, kNoCompression,
-                          CompressionOptions(), false /* skip_filters */,
-                          column_family_name, unknown_level),
+      TableBuilderOptions(
+          ioptions, moptions, ikc, &int_tbl_prop_collector_factories,
+          kNoCompression, 0 /* sample_for_compression */, CompressionOptions(),
+          false /* skip_filters */, column_family_name, unknown_level),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 
@@ -3256,8 +3256,8 @@ TEST_P(BlockBasedTableTest, DISABLED_TableWithGlobalSeqno) {
   std::unique_ptr<TableBuilder> builder(options.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, ikc,
                           &int_tbl_prop_collector_factories, kNoCompression,
-                          CompressionOptions(), false /* skip_filters */,
-                          column_family_name, -1),
+                          0 /* sample_for_compression */, CompressionOptions(),
+                          false /* skip_filters */, column_family_name, -1),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 
@@ -3436,8 +3436,8 @@ TEST_P(BlockBasedTableTest, BlockAlignTest) {
   std::unique_ptr<TableBuilder> builder(options.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, ikc,
                           &int_tbl_prop_collector_factories, kNoCompression,
-                          CompressionOptions(), false /* skip_filters */,
-                          column_family_name, -1),
+                          0 /* sample_for_compression */, CompressionOptions(),
+                          false /* skip_filters */, column_family_name, -1),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 
@@ -3529,8 +3529,8 @@ TEST_P(BlockBasedTableTest, PropertiesBlockRestartPointTest) {
   std::unique_ptr<TableBuilder> builder(options.table_factory->NewTableBuilder(
       TableBuilderOptions(ioptions, moptions, ikc,
                           &int_tbl_prop_collector_factories, kNoCompression,
-                          CompressionOptions(), false /* skip_filters */,
-                          column_family_name, -1),
+                          0 /* sample_for_compression */, CompressionOptions(),
+                          false /* skip_filters */, column_family_name, -1),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 

tools/db_bench_tool.cc

@@ -801,6 +801,8 @@ DEFINE_string(compression_type, "snappy",
 static enum rocksdb::CompressionType FLAGS_compression_type_e =
     rocksdb::kSnappyCompression;
 
+DEFINE_int64(sample_for_compression, 0, "Sample every N block for compression");
+
 DEFINE_int32(compression_level, rocksdb::CompressionOptions().level,
              "Compression level. The meaning of this value is library-"
              "dependent. If unset, we try to use the default for the library "
@@ -2195,6 +2197,8 @@ class Benchmark {
 
     auto compression = CompressionTypeToString(FLAGS_compression_type_e);
     fprintf(stdout, "Compression: %s\n", compression.c_str());
+    fprintf(stdout, "Compression sampling rate: %" PRId64 "\n",
+            FLAGS_sample_for_compression);
 
     switch (FLAGS_rep_factory) {
       case kPrefixHash:
@@ -2234,7 +2238,8 @@ class Benchmark {
       CompressionOptions opts;
       CompressionContext context(FLAGS_compression_type_e);
       CompressionInfo info(opts, context, CompressionDict::GetEmptyDict(),
-                           FLAGS_compression_type_e);
+                           FLAGS_compression_type_e,
+                           FLAGS_sample_for_compression);
       bool result = CompressSlice(info, Slice(input_str), &compressed);
 
       if (!result) {
@@ -3101,7 +3106,8 @@ void VerifyDBFromDB(std::string& truth_db_name) {
     CompressionOptions opts;
     CompressionContext context(FLAGS_compression_type_e);
     CompressionInfo info(opts, context, CompressionDict::GetEmptyDict(),
-                         FLAGS_compression_type_e);
+                         FLAGS_compression_type_e,
+                         FLAGS_sample_for_compression);
     // Compress 1G
     while (ok && bytes < int64_t(1) << 30) {
       compressed.clear();
@@ -3129,9 +3135,9 @@ void VerifyDBFromDB(std::string& truth_db_name) {
 
     CompressionContext compression_ctx(FLAGS_compression_type_e);
     CompressionOptions compression_opts;
-    CompressionInfo compression_info(compression_opts, compression_ctx,
-                                     CompressionDict::GetEmptyDict(),
-                                     FLAGS_compression_type_e);
+    CompressionInfo compression_info(
+        compression_opts, compression_ctx, CompressionDict::GetEmptyDict(),
+        FLAGS_compression_type_e, FLAGS_sample_for_compression);
     UncompressionContext uncompression_ctx(FLAGS_compression_type_e);
     UncompressionInfo uncompression_info(uncompression_ctx,
                                          UncompressionDict::GetEmptyDict(),
@@ -3488,6 +3494,7 @@ void VerifyDBFromDB(std::string& truth_db_name) {
     options.level0_slowdown_writes_trigger =
       FLAGS_level0_slowdown_writes_trigger;
     options.compression = FLAGS_compression_type_e;
+    options.sample_for_compression = FLAGS_sample_for_compression;
     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;

tools/sst_dump_test.cc

@@ -59,8 +59,9 @@ void createSST(const Options& opts, const std::string& file_name) {
   tb.reset(opts.table_factory->NewTableBuilder(
       TableBuilderOptions(
           imoptions, moptions, ikc, &int_tbl_prop_collector_factories,
-          CompressionType::kNoCompression, CompressionOptions(),
-          false /* skip_filters */, column_family_name, unknown_level),
+          CompressionType::kNoCompression, 0 /* sample_for_compression */,
+          CompressionOptions(), false /* skip_filters */, column_family_name,
+          unknown_level),
       TablePropertiesCollectorFactory::Context::kUnknownColumnFamily,
       file_writer.get()));
 

tools/sst_dump_tool.cc

@@ -214,10 +214,10 @@ int SstFileDumper::ShowAllCompressionSizes(
       CompressionOptions compress_opt;
       std::string column_family_name;
       int unknown_level = -1;
-      TableBuilderOptions tb_opts(imoptions, moptions, ikc,
-                                  &block_based_table_factories, i.first,
-                                  compress_opt, false /* skip_filters */,
-                                  column_family_name, unknown_level);
+      TableBuilderOptions tb_opts(
+          imoptions, moptions, ikc, &block_based_table_factories, i.first,
+          0 /* sample_for_compression */, compress_opt,
+          false /* skip_filters */, column_family_name, unknown_level);
       uint64_t file_size = CalculateCompressedTableSize(tb_opts, block_size);
       fprintf(stdout, "Compression: %s", i.second);
       fprintf(stdout, " Size: %" PRIu64 "\n", file_size);

util/compression.h

@@ -333,17 +333,24 @@ class CompressionInfo {
   const CompressionContext& context_;
   const CompressionDict& dict_;
   const CompressionType type_;
+  const uint64_t sample_for_compression_;
 
  public:
   CompressionInfo(const CompressionOptions& _opts,
                   const CompressionContext& _context,
-                  const CompressionDict& _dict, CompressionType _type)
-      : opts_(_opts), context_(_context), dict_(_dict), type_(_type) {}
+                  const CompressionDict& _dict, CompressionType _type,
+                  uint64_t _sample_for_compression)
+      : opts_(_opts),
+        context_(_context),
+        dict_(_dict),
+        type_(_type),
+        sample_for_compression_(_sample_for_compression) {}
 
   const CompressionOptions& options() const { return opts_; }
   const CompressionContext& context() const { return context_; }
   const CompressionDict& dict() const { return dict_; }
   CompressionType type() const { return type_; }
+  uint64_t SampleForCompression() const { return sample_for_compression_; }
 };
 
 class UncompressionContext {

utilities/blob_db/blob_db_impl.cc

@@ -755,9 +755,10 @@ Slice BlobDBImpl::GetCompressedSlice(const Slice& raw,
   CompressionType type = bdb_options_.compression;
   CompressionOptions opts;
   CompressionContext context(type);
-  CompressionInfo info(opts, context, CompressionDict::GetEmptyDict(), type);
-  CompressBlock(raw, info, &type, kBlockBasedTableVersionFormat,
-                compression_output);
+  CompressionInfo info(opts, context, CompressionDict::GetEmptyDict(), type,
+                       0 /* sample_for_compression */);
+  CompressBlock(raw, info, &type, kBlockBasedTableVersionFormat, false,
+                compression_output, nullptr, nullptr);
   return *compression_output;
 }