advanced_options.h

// Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
//  This source code is licensed under both the GPLv2 (found in the
//  COPYING file in the root directory) and Apache 2.0 License
//  (found in the LICENSE.Apache file in the root directory).
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#pragma once

#include <memory>

#include "rocksdb/cache.h"
#include "rocksdb/compression_type.h"
#include "rocksdb/memtablerep.h"
#include "rocksdb/universal_compaction.h"

namespace ROCKSDB_NAMESPACE {

class Slice;
class SliceTransform;
class TablePropertiesCollectorFactory;
class TableFactory;
struct Options;

enum CompactionStyle : char {
  // level based compaction style
  kCompactionStyleLevel = 0x0,
  // Universal compaction style
  // Not supported in ROCKSDB_LITE.
  kCompactionStyleUniversal = 0x1,
  // FIFO compaction style
  // Not supported in ROCKSDB_LITE
  kCompactionStyleFIFO = 0x2,
  // Disable background compaction. Compaction jobs are submitted
  // via CompactFiles().
  // Not supported in ROCKSDB_LITE
  kCompactionStyleNone = 0x3,
};

// In Level-based compaction, it Determines which file from a level to be
// picked to merge to the next level. We suggest people try
// kMinOverlappingRatio first when you tune your database.
enum CompactionPri : char {
  // Slightly prioritize larger files by size compensated by #deletes
  kByCompensatedSize = 0x0,
  // First compact files whose data's latest update time is oldest.
  // Try this if you only update some hot keys in small ranges.
  kOldestLargestSeqFirst = 0x1,
  // First compact files whose range hasn't been compacted to the next level
  // for the longest. If your updates are random across the key space,
  // write amplification is slightly better with this option.
  kOldestSmallestSeqFirst = 0x2,
  // First compact files whose ratio between overlapping size in next level
  // and its size is the smallest. It in many cases can optimize write
  // amplification.
  kMinOverlappingRatio = 0x3,
  // Keeps a cursor(s) of the successor of the file (key range) was/were
  // compacted before, and always picks the next files (key range) in that
  // level. The file picking process will cycle through all the files in a
  // round-robin manner.
  kRoundRobin = 0x4,
};

struct CompactionOptionsFIFO {
  // once the total sum of table files reaches this, we will delete the oldest
  // table file
  // Default: 1GB
  uint64_t max_table_files_size;

  // If true, try to do compaction to compact smaller files into larger ones.
  // Minimum files to compact follows options.level0_file_num_compaction_trigger
  // and compaction won't trigger if average compact bytes per del file is
  // larger than options.write_buffer_size. This is to protect large files
  // from being compacted again.
  // Default: false;
  bool allow_compaction = false;

  // When not 0, if the data in the file is older than this threshold, RocksDB
  // will soon move the file to warm temperature.
  uint64_t age_for_warm = 0;

  CompactionOptionsFIFO() : max_table_files_size(1 * 1024 * 1024 * 1024) {}
  CompactionOptionsFIFO(uint64_t _max_table_files_size, bool _allow_compaction)
      : max_table_files_size(_max_table_files_size),
        allow_compaction(_allow_compaction) {}
};

// Compression options for different compression algorithms like Zlib
struct CompressionOptions {
  // RocksDB's generic default compression level. Internally it'll be translated
  // to the default compression level specific to the library being used (see
  // comment above `ColumnFamilyOptions::compression`).
  //
  // The default value is the max 16-bit int as it'll be written out in OPTIONS
  // file, which should be portable.
  const static int kDefaultCompressionLevel = 32767;

  int window_bits;
  int level;
  int strategy;

  // Maximum size of dictionaries used to prime the compression library.
  // Enabling dictionary can improve compression ratios when there are
  // repetitions across data blocks.
  //
  // The dictionary is created by sampling the SST file data. If
  // `zstd_max_train_bytes` is nonzero, the samples are passed through zstd's
  // dictionary generator (see comments for option `use_zstd_dict_trainer` for
  // detail on dictionary generator). If `zstd_max_train_bytes` is zero, the
  // random samples are used directly as the dictionary.
  //
  // When compression dictionary is disabled, we compress and write each block
  // before buffering data for the next one. When compression dictionary is
  // enabled, we buffer SST file data in-memory so we can sample it, as data
  // can only be compressed and written after the dictionary has been finalized.
  //
  // The amount of data buffered can be limited by `max_dict_buffer_bytes`. This
  // buffered memory is charged to the block cache when there is a block cache.
  // If block cache insertion fails with `Status::MemoryLimit` (i.e., it is
  // full), we finalize the dictionary with whatever data we have and then stop
  // buffering.
  //
  // Default: 0.
  uint32_t max_dict_bytes;

  // Maximum size of training data passed to zstd's dictionary trainer. Using
  // zstd's dictionary trainer can achieve even better compression ratio
  // improvements than using `max_dict_bytes` alone.
  //
  // The training data will be used to generate a dictionary of max_dict_bytes.
  //
  // Default: 0.
  uint32_t zstd_max_train_bytes;

  // Number of threads for parallel compression.
  // Parallel compression is enabled only if threads > 1.
  // THE FEATURE IS STILL EXPERIMENTAL
  //
  // This option is valid only when BlockBasedTable is used.
  //
  // When parallel compression is enabled, SST size file sizes might be
  // more inflated compared to the target size, because more data of unknown
  // compressed size is in flight when compression is parallelized. To be
  // reasonably accurate, this inflation is also estimated by using historical
  // compression ratio and current bytes inflight.
  //
  // Default: 1.
  uint32_t parallel_threads;

  // When the compression options are set by the user, it will be set to "true".
  // For bottommost_compression_opts, to enable it, user must set enabled=true.
  // Otherwise, bottommost compression will use compression_opts as default
  // compression options.
  //
  // For compression_opts, if compression_opts.enabled=false, it is still
  // used as compression options for compression process.
  //
  // Default: false.
  bool enabled;

  // Limit on data buffering when gathering samples to build a dictionary. Zero
  // means no limit. When dictionary is disabled (`max_dict_bytes == 0`),
  // enabling this limit (`max_dict_buffer_bytes != 0`) has no effect.
  //
  // In compaction, the buffering is limited to the target file size (see
  // `target_file_size_base` and `target_file_size_multiplier`) even if this
  // setting permits more buffering. Since we cannot determine where the file
  // should be cut until data blocks are compressed with dictionary, buffering
  // more than the target file size could lead to selecting samples that belong
  // to a later output SST.
  //
  // Limiting too strictly may harm dictionary effectiveness since it forces
  // RocksDB to pick samples from the initial portion of the output SST, which
  // may not be representative of the whole file. Configuring this limit below
  // `zstd_max_train_bytes` (when enabled) can restrict how many samples we can
  // pass to the dictionary trainer. Configuring it below `max_dict_bytes` can
  // restrict the size of the final dictionary.
  //
  // Default: 0 (unlimited)
  uint64_t max_dict_buffer_bytes;

  // Use zstd trainer to generate dictionaries. When this option is set to true,
  // zstd_max_train_bytes of training data sampled from max_dict_buffer_bytes
  // buffered data will be passed to zstd dictionary trainer to generate a
  // dictionary of size max_dict_bytes.
  //
  // When this option is false, zstd's API ZDICT_finalizeDictionary() will be
  // called to generate dictionaries. zstd_max_train_bytes of training sampled
  // data will be passed to this API. Using this API should save CPU time on
  // dictionary training, but the compression ratio may not be as good as using
  // a dictionary trainer.
  //
  // Default: true
  bool use_zstd_dict_trainer;

  CompressionOptions()
      : window_bits(-14),
        level(kDefaultCompressionLevel),
        strategy(0),
        max_dict_bytes(0),
        zstd_max_train_bytes(0),
        parallel_threads(1),
        enabled(false),
        max_dict_buffer_bytes(0),
        use_zstd_dict_trainer(true) {}
  CompressionOptions(int wbits, int _lev, int _strategy,
                     uint32_t _max_dict_bytes, uint32_t _zstd_max_train_bytes,
                     uint32_t _parallel_threads, bool _enabled,
                     uint64_t _max_dict_buffer_bytes,
                     bool _use_zstd_dict_trainer)
      : window_bits(wbits),
        level(_lev),
        strategy(_strategy),
        max_dict_bytes(_max_dict_bytes),
        zstd_max_train_bytes(_zstd_max_train_bytes),
        parallel_threads(_parallel_threads),
        enabled(_enabled),
        max_dict_buffer_bytes(_max_dict_buffer_bytes),
        use_zstd_dict_trainer(_use_zstd_dict_trainer) {}
};

// Temperature of a file. Used to pass to FileSystem for a different
// placement and/or coding.
// Reserve some numbers in the middle, in case we need to insert new tier
// there.
enum class Temperature : uint8_t {
  kUnknown = 0,
  kHot = 0x04,
  kWarm = 0x08,
  kCold = 0x0C,
  kLastTemperature,
};

// The control option of how the cache tiers will be used. Currently rocksdb
// support block cache (volatile tier), secondary cache (non-volatile tier).
// In the future, we may add more caching layers.
enum class CacheTier : uint8_t {
  kVolatileTier = 0,
  kNonVolatileBlockTier = 0x01,
};

enum UpdateStatus {    // Return status For inplace update callback
  UPDATE_FAILED   = 0, // Nothing to update
  UPDATED_INPLACE = 1, // Value updated inplace
  UPDATED         = 2, // No inplace update. Merged value set
};

enum class PrepopulateBlobCache : uint8_t {
  kDisable = 0x0,    // Disable prepopulate blob cache
  kFlushOnly = 0x1,  // Prepopulate blobs during flush only
};

struct AdvancedColumnFamilyOptions {
  // The maximum number of write buffers that are built up in memory.
  // The default and the minimum number is 2, so that when 1 write buffer
  // is being flushed to storage, new writes can continue to the other
  // write buffer.
  // If max_write_buffer_number > 3, writing will be slowed down to
  // options.delayed_write_rate if we are writing to the last write buffer
  // allowed.
  //
  // Default: 2
  //
  // Dynamically changeable through SetOptions() API
  int max_write_buffer_number = 2;

  // The minimum number of write buffers that will be merged together
  // before writing to storage.  If set to 1, then
  // all write buffers are flushed to L0 as individual files and this increases
  // read amplification because a get request has to check in all of these
  // files. Also, an in-memory merge may result in writing lesser
  // data to storage if there are duplicate records in each of these
  // individual write buffers.  Default: 1
  int min_write_buffer_number_to_merge = 1;

  // DEPRECATED
  // The total maximum number of write buffers to maintain in memory including
  // copies of buffers that have already been flushed.  Unlike
  // max_write_buffer_number, this parameter does not affect flushing.
  // This parameter is being replaced by max_write_buffer_size_to_maintain.
  // If both parameters are set to non-zero values, this parameter will be
  // ignored.
  int max_write_buffer_number_to_maintain = 0;

  // The target number of write history bytes to hold in memory. Write history
  // comprises the latest write buffers (memtables). To reach the target, write
  // buffers that were most recently flushed to SST files may be retained in
  // memory.
  //
  // This controls the target amount of write history that will be available
  // in memory for conflict checking when Transactions are used.
  //
  // This target may be undershot when the CF first opens and has not recovered
  // or received enough writes to reach the target. After reaching the target
  // once, it is guaranteed to never undershoot again. That guarantee is
  // implemented by retaining flushed write buffers in-memory until the oldest
  // one can be trimmed without dropping below the target.
  //
  // Examples with `max_write_buffer_size_to_maintain` set to 32MB:
  //
  // - One mutable memtable of 64MB, one unflushed immutable memtable of 64MB,
  //   and zero flushed immutable memtables. Nothing trimmable exists.
  // - One mutable memtable of 16MB, zero unflushed immutable memtables, and
  //   one flushed immutable memtable of 64MB. Trimming is disallowed because
  //   dropping the earliest (only) flushed immutable memtable would result in
  //   write history of 16MB < 32MB.
  // - One mutable memtable of 24MB, one unflushed immutable memtable of 16MB,
  //   and one flushed immutable memtable of 16MB. The earliest (only) flushed
  //   immutable memtable is trimmed because without it we still have
  //   16MB + 24MB = 40MB > 32MB of write history.
  //
  // When using an OptimisticTransactionDB:
  // If this value is too low, some transactions may fail at commit time due
  // to not being able to determine whether there were any write conflicts.
  //
  // When using a TransactionDB:
  // If Transaction::SetSnapshot is used, TransactionDB will read either
  // in-memory write buffers or SST files to do write-conflict checking.
  // Increasing this value can reduce the number of reads to SST files
  // done for conflict detection.
  //
  // Setting this value to 0 will cause write buffers to be freed immediately
  // after they are flushed. If this value is set to -1,
  // 'max_write_buffer_number * write_buffer_size' will be used.
  //
  // Default:
  // If using a TransactionDB/OptimisticTransactionDB, the default value will
  // be set to the value of 'max_write_buffer_number * write_buffer_size'
  // if it is not explicitly set by the user.  Otherwise, the default is 0.
  int64_t max_write_buffer_size_to_maintain = 0;

  // Allows thread-safe inplace updates. If this is true, there is no way to
  // achieve point-in-time consistency using snapshot or iterator (assuming
  // concurrent updates). Hence iterator and multi-get will return results
  // which are not consistent as of any point-in-time.
  // Backward iteration on memtables will not work either.
  // If inplace_callback function is not set,
  //   Put(key, new_value) will update inplace the existing_value iff
  //   * key exists in current memtable
  //   * new sizeof(new_value) <= sizeof(existing_value)
  //   * existing_value for that key is a put i.e. kTypeValue
  // If inplace_callback function is set, check doc for inplace_callback.
  // Default: false.
  bool inplace_update_support = false;

  // Number of locks used for inplace update
  // Default: 10000, if inplace_update_support = true, else 0.
  //
  // Dynamically changeable through SetOptions() API
  size_t inplace_update_num_locks = 10000;

  // [experimental]
  // Used to activate or deactive the Mempurge feature (memtable garbage
  // collection). (deactivated by default). At every flush, the total useful
  // payload (total entries minus garbage entries) is estimated as a ratio
  // [useful payload bytes]/[size of a memtable (in bytes)]. This ratio is then
  // compared to this `threshold` value:
  //     - if ratio<threshold: the flush is replaced by a mempurge operation
  //     - else: a regular flush operation takes place.
  // Threshold values:
  //   0.0: mempurge deactivated (default).
  //   1.0: recommended threshold value.
  //   >1.0 : aggressive mempurge.
  //   0 < threshold < 1.0: mempurge triggered only for very low useful payload
  //   ratios.
  // [experimental]
  double experimental_mempurge_threshold = 0.0;

  // existing_value - pointer to previous value (from both memtable and sst).
  //                  nullptr if key doesn't exist
  // existing_value_size - pointer to size of existing_value).
  //                       nullptr if key doesn't exist
  // delta_value - Delta value to be merged with the existing_value.
  //               Stored in transaction logs.
  // merged_value - Set when delta is applied on the previous value.
  //
  // Applicable only when inplace_update_support is true,
  // this callback function is called at the time of updating the memtable
  // as part of a Put operation, lets say Put(key, delta_value). It allows the
  // 'delta_value' specified as part of the Put operation to be merged with
  // an 'existing_value' of the key in the database.
  //
  // If the merged value is smaller in size that the 'existing_value',
  // then this function can update the 'existing_value' buffer inplace and
  // the corresponding 'existing_value'_size pointer, if it wishes to.
  // The callback should return UpdateStatus::UPDATED_INPLACE.
  // In this case. (In this case, the snapshot-semantics of the rocksdb
  // Iterator is not atomic anymore).
  //
  // If the merged value is larger in size than the 'existing_value' or the
  // application does not wish to modify the 'existing_value' buffer inplace,
  // then the merged value should be returned via *merge_value. It is set by
  // merging the 'existing_value' and the Put 'delta_value'. The callback should
  // return UpdateStatus::UPDATED in this case. This merged value will be added
  // to the memtable.
  //
  // If merging fails or the application does not wish to take any action,
  // then the callback should return UpdateStatus::UPDATE_FAILED.
  //
  // Please remember that the original call from the application is Put(key,
  // delta_value). So the transaction log (if enabled) will still contain (key,
  // delta_value). The 'merged_value' is not stored in the transaction log.
  // Hence the inplace_callback function should be consistent across db reopens.
  //
  // RocksDB callbacks are NOT exception-safe. A callback completing with an
  // exception can lead to undefined behavior in RocksDB, including data loss,
  // unreported corruption, deadlocks, and more.
  //
  // Default: nullptr
  UpdateStatus (*inplace_callback)(char* existing_value,
                                   uint32_t* existing_value_size,
                                   Slice delta_value,
                                   std::string* merged_value) = nullptr;

  // Should really be called `memtable_bloom_size_ratio`. Enables a dynamic
  // Bloom filter in memtable to optimize many queries that must go beyond
  // the memtable. The size in bytes of the filter is
  // write_buffer_size * memtable_prefix_bloom_size_ratio.
  // * If prefix_extractor is set, the filter includes prefixes.
  // * If memtable_whole_key_filtering, the filter includes whole keys.
  // * If both, the filter includes both.
  // * If neither, the feature is disabled.
  //
  // If this value is larger than 0.25, it is sanitized to 0.25.
  //
  // Default: 0 (disabled)
  //
  // Dynamically changeable through SetOptions() API
  double memtable_prefix_bloom_size_ratio = 0.0;

  // Enable whole key bloom filter in memtable. Note this will only take effect
  // if memtable_prefix_bloom_size_ratio is not 0. Enabling whole key filtering
  // can potentially reduce CPU usage for point-look-ups.
  //
  // Default: false (disabled)
  //
  // Dynamically changeable through SetOptions() API
  bool memtable_whole_key_filtering = false;

  // Page size for huge page for the arena used by the memtable. If <=0, it
  // won't allocate from huge page but from malloc.
  // Users are responsible to reserve huge pages for it to be allocated. For
  // example:
  //      sysctl -w vm.nr_hugepages=20
  // See linux doc Documentation/vm/hugetlbpage.txt
  // If there isn't enough free huge page available, it will fall back to
  // malloc.
  //
  // Dynamically changeable through SetOptions() API
  size_t memtable_huge_page_size = 0;

  // If non-nullptr, memtable will use the specified function to extract
  // prefixes for keys, and for each prefix maintain a hint of insert location
  // to reduce CPU usage for inserting keys with the prefix. Keys out of
  // domain of the prefix extractor will be insert without using hints.
  //
  // Currently only the default skiplist based memtable implements the feature.
  // All other memtable implementation will ignore the option. It incurs ~250
  // additional bytes of memory overhead to store a hint for each prefix.
  // Also concurrent writes (when allow_concurrent_memtable_write is true) will
  // ignore the option.
  //
  // The option is best suited for workloads where keys will likely to insert
  // to a location close the last inserted key with the same prefix.
  // One example could be inserting keys of the form (prefix + timestamp),
  // and keys of the same prefix always comes in with time order. Another
  // example would be updating the same key over and over again, in which case
  // the prefix can be the key itself.
  //
  // Default: nullptr (disabled)
  std::shared_ptr<const SliceTransform>
      memtable_insert_with_hint_prefix_extractor = nullptr;

  // Control locality of bloom filter probes to improve CPU cache hit rate.
  // This option now only applies to plaintable prefix bloom. This
  // optimization is turned off when set to 0, and positive number to turn
  // it on.
  // Default: 0
  uint32_t bloom_locality = 0;

  // size of one block in arena memory allocation.
  // If <= 0, a proper value is automatically calculated (usually 1/8 of
  // writer_buffer_size, rounded up to a multiple of 4KB, or 1MB which ever is
  // smaller).
  //
  // There are two additional restriction of the specified size:
  // (1) size should be in the range of [4096, 2 << 30] and
  // (2) be the multiple of the CPU word (which helps with the memory
  // alignment).
  //
  // We'll automatically check and adjust the size number to make sure it
  // conforms to the restrictions.
  //
  // Default: 0
  //
  // Dynamically changeable through SetOptions() API
  size_t arena_block_size = 0;

  // Different levels can have different compression policies. There
  // are cases where most lower levels would like to use quick compression
  // algorithms while the higher levels (which have more data) use
  // compression algorithms that have better compression but could
  // be slower. This array, if non-empty, should have an entry for
  // each level of the database; these override the value specified in
  // the previous field 'compression'.
  //
  // NOTICE if level_compaction_dynamic_level_bytes=true,
  // compression_per_level[0] still determines L0, but other elements
  // of the array are based on base level (the level L0 files are merged
  // to), and may not match the level users see from info log for metadata.
  // If L0 files are merged to level-n, then, for i>0, compression_per_level[i]
  // determines compaction type for level n+i-1.
  // For example, if we have three 5 levels, and we determine to merge L0
  // data to L4 (which means L1..L3 will be empty), then the new files go to
  // L4 uses compression type compression_per_level[1].
  // If now L0 is merged to L2. Data goes to L2 will be compressed
  // according to compression_per_level[1], L3 using compression_per_level[2]
  // and L4 using compression_per_level[3]. Compaction for each level can
  // change when data grows.
  //
  // NOTE: if the vector size is smaller than the level number, the undefined
  // lower level uses the last option in the vector, for example, for 3 level
  // LSM tree the following settings are the same:
  // {kNoCompression, kSnappyCompression}
  // {kNoCompression, kSnappyCompression, kSnappyCompression}
  //
  // Dynamically changeable through SetOptions() API
  std::vector<CompressionType> compression_per_level;

  // Number of levels for this database
  int num_levels = 7;

  // Soft limit on number of level-0 files. We start slowing down writes at this
  // point. A value <0 means that no writing slow down will be triggered by
  // number of files in level-0.
  //
  // Default: 20
  //
  // Dynamically changeable through SetOptions() API
  int level0_slowdown_writes_trigger = 20;

  // Maximum number of level-0 files.  We stop writes at this point.
  //
  // Default: 36
  //
  // Dynamically changeable through SetOptions() API
  int level0_stop_writes_trigger = 36;

  // Target file size for compaction.
  // target_file_size_base is per-file size for level-1.
  // Target file size for level L can be calculated by
  // target_file_size_base * (target_file_size_multiplier ^ (L-1))
  // For example, if target_file_size_base is 2MB and
  // target_file_size_multiplier is 10, then each file on level-1 will
  // be 2MB, and each file on level 2 will be 20MB,
  // and each file on level-3 will be 200MB.
  //
  // Default: 64MB.
  //
  // Dynamically changeable through SetOptions() API
  uint64_t target_file_size_base = 64 * 1048576;

  // By default target_file_size_multiplier is 1, which means
  // by default files in different levels will have similar size.
  //
  // Dynamically changeable through SetOptions() API
  int target_file_size_multiplier = 1;

  // If true, RocksDB will pick target size of each level dynamically.
  // We will pick a base level b >= 1. L0 will be directly merged into level b,
  // instead of always into level 1. Level 1 to b-1 need to be empty.
  // We try to pick b and its target size so that
  // 1. target size is in the range of
  //   (max_bytes_for_level_base / max_bytes_for_level_multiplier,
  //    max_bytes_for_level_base]
  // 2. target size of the last level (level num_levels-1) equals to extra size
  //    of the level.
  // At the same time max_bytes_for_level_multiplier and
  // max_bytes_for_level_multiplier_additional are still satisfied.
  // (When L0 is too large, we make some adjustment. See below.)
  //
  // With this option on, from an empty DB, we make last level the base level,
  // which means merging L0 data into the last level, until it exceeds
  // max_bytes_for_level_base. And then we make the second last level to be
  // base level, to start to merge L0 data to second last level, with its
  // target size to be 1/max_bytes_for_level_multiplier of the last level's
  // extra size. After the data accumulates more so that we need to move the
  // base level to the third last one, and so on.
  //
  // For example, assume max_bytes_for_level_multiplier=10, num_levels=6,
  // and max_bytes_for_level_base=10MB.
  // Target sizes of level 1 to 5 starts with:
  // [- - - - 10MB]
  // with base level is level. Target sizes of level 1 to 4 are not applicable
  // because they will not be used.
  // Until the size of Level 5 grows to more than 10MB, say 11MB, we make
  // base target to level 4 and now the targets looks like:
  // [- - - 1.1MB 11MB]
  // While data are accumulated, size targets are tuned based on actual data
  // of level 5. When level 5 has 50MB of data, the target is like:
  // [- - - 5MB 50MB]
  // Until level 5's actual size is more than 100MB, say 101MB. Now if we keep
  // level 4 to be the base level, its target size needs to be 10.1MB, which
  // doesn't satisfy the target size range. So now we make level 3 the target
  // size and the target sizes of the levels look like:
  // [- - 1.01MB 10.1MB 101MB]
  // In the same way, while level 5 further grows, all levels' targets grow,
  // like
  // [- - 5MB 50MB 500MB]
  // Until level 5 exceeds 1000MB and becomes 1001MB, we make level 2 the
  // base level and make levels' target sizes like this:
  // [- 1.001MB 10.01MB 100.1MB 1001MB]
  // and go on...
  //
  // By doing it, we give max_bytes_for_level_multiplier a priority against
  // max_bytes_for_level_base, for a more predictable LSM tree shape. It is
  // useful to limit worse case space amplification.
  //
  //
  // If the compaction from L0 is lagged behind, a special mode will be turned
  // on to prioritize write amplification against max_bytes_for_level_multiplier
  // or max_bytes_for_level_base. The L0 compaction is lagged behind by looking
  // at number of L0 files and total L0 size. If number of L0 files is at least
  // the double of level0_file_num_compaction_trigger, or the total size is
  // at least max_bytes_for_level_base, this mode is on. The target of L1 grows
  // to the actual data size in L0, and then determine the target for each level
  // so that each level will have the same level multiplier.
  //
  // For example, when L0 size is 100MB, the size of last level is 1600MB,
  // max_bytes_for_level_base = 80MB, and max_bytes_for_level_multiplier = 10.
  // Since L0 size is larger than max_bytes_for_level_base, this is a L0
  // compaction backlogged mode. So that the L1 size is determined to be 100MB.
  // Based on max_bytes_for_level_multiplier = 10, at least 3 non-0 levels will
  // be needed. The level multiplier will be calculated to be 4 and the three
  // levels' target to be [100MB, 400MB, 1600MB].
  //
  // In this mode, The number of levels will be no more than the normal mode,
  // and the level multiplier will be lower. The write amplification will
  // likely to be reduced.
  //
  //
  // max_bytes_for_level_multiplier_additional is ignored with this flag on.
  //
  // Turning this feature on or off for an existing DB can cause unexpected
  // LSM tree structure so it's not recommended.
  //
  // Default: false
  bool level_compaction_dynamic_level_bytes = false;

  // Default: 10.
  //
  // Dynamically changeable through SetOptions() API
  double max_bytes_for_level_multiplier = 10;

  // Different max-size multipliers for different levels.
  // These are multiplied by max_bytes_for_level_multiplier to arrive
  // at the max-size of each level.
  //
  // Default: 1
  //
  // Dynamically changeable through SetOptions() API
  std::vector<int> max_bytes_for_level_multiplier_additional =
      std::vector<int>(num_levels, 1);

  // We try to limit number of bytes in one compaction to be lower than this
  // threshold. But it's not guaranteed.
  // Value 0 will be sanitized.
  //
  // Default: target_file_size_base * 25
  //
  // Dynamically changeable through SetOptions() API
  uint64_t max_compaction_bytes = 0;

  // All writes will be slowed down to at least delayed_write_rate if estimated
  // bytes needed to be compaction exceed this threshold.
  //
  // Default: 64GB
  //
  // Dynamically changeable through SetOptions() API
  uint64_t soft_pending_compaction_bytes_limit = 64 * 1073741824ull;

  // All writes are stopped if estimated bytes needed to be compaction exceed
  // this threshold.
  //
  // Default: 256GB
  //
  // Dynamically changeable through SetOptions() API
  uint64_t hard_pending_compaction_bytes_limit = 256 * 1073741824ull;

  // The compaction style. Default: kCompactionStyleLevel
  CompactionStyle compaction_style = kCompactionStyleLevel;

  // If level compaction_style = kCompactionStyleLevel, for each level,
  // which files are prioritized to be picked to compact.
  // Default: kMinOverlappingRatio
  CompactionPri compaction_pri = kMinOverlappingRatio;

  // The options needed to support Universal Style compactions
  //
  // Dynamically changeable through SetOptions() API
  // Dynamic change example:
  // SetOptions("compaction_options_universal", "{size_ratio=2;}")
  CompactionOptionsUniversal compaction_options_universal;

  // The options for FIFO compaction style
  //
  // Dynamically changeable through SetOptions() API
  // Dynamic change example:
  // SetOptions("compaction_options_fifo", "{max_table_files_size=100;}")
  CompactionOptionsFIFO compaction_options_fifo;

  // An iteration->Next() sequentially skips over keys with the same
  // user-key unless this option is set. This number specifies the number
  // of keys (with the same userkey) that will be sequentially
  // skipped before a reseek is issued.
  //
  // Default: 8
  //
  // Dynamically changeable through SetOptions() API
  uint64_t max_sequential_skip_in_iterations = 8;

  // This is a factory that provides MemTableRep objects.
  // Default: a factory that provides a skip-list-based implementation of
  // MemTableRep.
  std::shared_ptr<MemTableRepFactory> memtable_factory =
      std::shared_ptr<SkipListFactory>(new SkipListFactory);

  // Block-based table related options are moved to BlockBasedTableOptions.
  // Related options that were originally here but now moved include:
  //   no_block_cache
  //   block_cache
  //   block_cache_compressed
  //   block_size
  //   block_size_deviation
  //   block_restart_interval
  //   filter_policy
  //   whole_key_filtering
  // If you'd like to customize some of these options, you will need to
  // use NewBlockBasedTableFactory() to construct a new table factory.

  // This option allows user to collect their own interested statistics of
  // the tables.
  // Default: empty vector -- no user-defined statistics collection will be
  // performed.
  using TablePropertiesCollectorFactories =
      std::vector<std::shared_ptr<TablePropertiesCollectorFactory>>;
  TablePropertiesCollectorFactories table_properties_collector_factories;

  // Maximum number of successive merge operations on a key in the memtable.
  //
  // When a merge operation is added to the memtable and the maximum number of
  // successive merges is reached, the value of the key will be calculated and
  // inserted into the memtable instead of the merge operation. This will
  // ensure that there are never more than max_successive_merges merge
  // operations in the memtable.
  //
  // Default: 0 (disabled)
  //
  // Dynamically changeable through SetOptions() API
  size_t max_successive_merges = 0;

  // This flag specifies that the implementation should optimize the filters
  // mainly for cases where keys are found rather than also optimize for keys
  // missed. This would be used in cases where the application knows that
  // there are very few misses or the performance in the case of misses is not
  // important.
  //
  // For now, this flag allows us to not store filters for the last level i.e
  // the largest level which contains data of the LSM store. For keys which
  // are hits, the filters in this level are not useful because we will search
  // for the data anyway. NOTE: the filters in other levels are still useful
  // even for key hit because they tell us whether to look in that level or go
  // to the higher level.
  //
  // Default: false
  bool optimize_filters_for_hits = false;

  // During flush or compaction, check whether keys inserted to output files
  // are in order.
  //
  // Default: true
  //
  // Dynamically changeable through SetOptions() API
  bool check_flush_compaction_key_order = true;

  // After writing every SST file, reopen it and read all the keys.
  // Checks the hash of all of the keys and values written versus the
  // keys in the file and signals a corruption if they do not match
  //
  // Default: false
  //
  // Dynamically changeable through SetOptions() API
  bool paranoid_file_checks = false;

  // In debug mode, RocksDB runs consistency checks on the LSM every time the
  // LSM changes (Flush, Compaction, AddFile). When this option is true, these
  // checks are also enabled in release mode. These checks were historically
  // disabled in release mode, but are now enabled by default for proactive
  // corruption detection. The CPU overhead is negligible for normal mixed
  // operations but can slow down saturated writing. See
  // Options::DisableExtraChecks().
  // Default: true
  bool force_consistency_checks = true;

  // Measure IO stats in compactions and flushes, if true.
  //
  // Default: false
  //
  // Dynamically changeable through SetOptions() API
  bool report_bg_io_stats = false;

  // Files containing updates older than TTL will go through the compaction
  // process. This usually happens in a cascading way so that those entries
  // will be compacted to bottommost level/file.
  // The feature is used to remove stale entries that have been deleted or
  // updated from the file system.
  // Pre-req: This needs max_open_files to be set to -1.
  // In Level: Non-bottom-level files older than TTL will go through the
  //           compaction process.
  // In FIFO: Files older than TTL will be deleted.
  // unit: seconds. Ex: 1 day = 1 * 24 * 60 * 60
  // In FIFO, this option will have the same meaning as
  // periodic_compaction_seconds. Whichever stricter will be used.
  // 0 means disabling.
  // UINT64_MAX - 1 (0xfffffffffffffffe) is special flag to allow RocksDB to
  // pick default.
  //
  // Default: 30 days for leveled compaction + block based table. disable
  //          otherwise.
  //
  // Dynamically changeable through SetOptions() API
  uint64_t ttl = 0xfffffffffffffffe;

  // Files older than this value will be picked up for compaction, and
  // re-written to the same level as they were before.
  // One main use of the feature is to make sure a file goes through compaction
  // filters periodically. Users can also use the feature to clear up SST
  // files using old format.
  //
  // A file's age is computed by looking at file_creation_time or creation_time
  // table properties in order, if they have valid non-zero values; if not, the
  // age is based on the file's last modified time (given by the underlying
  // Env).
  //
  // Supported in Level and FIFO compaction.
  // In FIFO compaction, this option has the same meaning as TTL and whichever
  // stricter will be used.
  // Pre-req: max_open_file == -1.
  // unit: seconds. Ex: 7 days = 7 * 24 * 60 * 60
  //
  // Values:
  // 0: Turn off Periodic compactions.
  // UINT64_MAX - 1 (i.e 0xfffffffffffffffe): Let RocksDB control this feature
  //     as needed. For now, RocksDB will change this value to 30 days
  //     (i.e 30 * 24 * 60 * 60) so that every file goes through the compaction
  //     process at least once every 30 days if not compacted sooner.
  //     In FIFO compaction, since the option has the same meaning as ttl,
  //     when this value is left default, and ttl is left to 0, 30 days will be
  //     used. Otherwise, min(ttl, periodic_compaction_seconds) will be used.
  //
  // Default: UINT64_MAX - 1 (allow RocksDB to auto-tune)
  //
  // Dynamically changeable through SetOptions() API
  uint64_t periodic_compaction_seconds = 0xfffffffffffffffe;

  // 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;

  // EXPERIMENTAL
  // The feature is still in development and is incomplete.
  // If this option is set, when creating bottommost files, pass this
  // temperature to FileSystem used. Should be no-op for default FileSystem
  // and users need to plug in their own FileSystem to take advantage of it.
  //
  // Dynamically changeable through the SetOptions() API
  Temperature bottommost_temperature = Temperature::kUnknown;

  // EXPERIMENTAL
  // The feature is still in development and is incomplete.
  // If this option is set, when data insert time is within this time range, it
  // will be precluded from the last level.
  // 0 means no key will be precluded from the last level.
  //
  // Note: when enabled, universal size amplification (controlled by option
  //  `compaction_options_universal.max_size_amplification_percent`) calculation
  //  will exclude the last level. As the feature is designed for tiered storage
  //  and a typical setting is the last level is cold tier which is likely not
  //  size constrained, the size amp is going to be only for non-last levels.
  //
  // Default: 0 (disable the feature)
  uint64_t preclude_last_level_data_seconds = 0;

  // When set, large values (blobs) are written to separate blob files, and
  // only pointers to them are stored in SST files. This can reduce write
  // amplification for large-value use cases at the cost of introducing a level
  // of indirection for reads. See also the options min_blob_size,
  // blob_file_size, blob_compression_type, enable_blob_garbage_collection,
  // blob_garbage_collection_age_cutoff,
  // blob_garbage_collection_force_threshold, and blob_compaction_readahead_size
  // below.
  //
  // Default: false
  //
  // Dynamically changeable through the SetOptions() API
  bool enable_blob_files = false;

  // The size of the smallest value to be stored separately in a blob file.
  // Values which have an uncompressed size smaller than this threshold are
  // stored alongside the keys in SST files in the usual fashion. A value of
  // zero for this option means that all values are stored in blob files. Note
  // that enable_blob_files has to be set in order for this option to have any
  // effect.
  //
  // Default: 0
  //
  // Dynamically changeable through the SetOptions() API
  uint64_t min_blob_size = 0;

  // The size limit for blob files. When writing blob files, a new file is
  // opened once this limit is reached. Note that enable_blob_files has to be
  // set in order for this option to have any effect.
  //
  // Default: 256 MB
  //
  // Dynamically changeable through the SetOptions() API
  uint64_t blob_file_size = 1ULL << 28;

  // The compression algorithm to use for large values stored in blob files.
  // Note that enable_blob_files has to be set in order for this option to have
  // any effect.
  //
  // Default: no compression
  //
  // Dynamically changeable through the SetOptions() API
  CompressionType blob_compression_type = kNoCompression;

  // Enables garbage collection of blobs. Blob GC is performed as part of
  // compaction. Valid blobs residing in blob files older than a cutoff get
  // relocated to new files as they are encountered during compaction, which
  // makes it possible to clean up blob files once they contain nothing but
  // obsolete/garbage blobs. See also blob_garbage_collection_age_cutoff and
  // blob_garbage_collection_force_threshold below.
  //
  // Default: false
  //
  // Dynamically changeable through the SetOptions() API
  bool enable_blob_garbage_collection = false;

  // The cutoff in terms of blob file age for garbage collection. Blobs in
  // the oldest N blob files will be relocated when encountered during
  // compaction, where N = garbage_collection_cutoff * number_of_blob_files.
  // Note that enable_blob_garbage_collection has to be set in order for this
  // option to have any effect.
  //
  // Default: 0.25
  //
  // Dynamically changeable through the SetOptions() API
  double blob_garbage_collection_age_cutoff = 0.25;

  // If the ratio of garbage in the oldest blob files exceeds this threshold,
  // targeted compactions are scheduled in order to force garbage collecting
  // the blob files in question, assuming they are all eligible based on the
  // value of blob_garbage_collection_age_cutoff above. This option is
  // currently only supported with leveled compactions.
  // Note that enable_blob_garbage_collection has to be set in order for this
  // option to have any effect.
  //
  // Default: 1.0
  //
  // Dynamically changeable through the SetOptions() API
  double blob_garbage_collection_force_threshold = 1.0;

  // Compaction readahead for blob files.
  //
  // Default: 0
  //
  // Dynamically changeable through the SetOptions() API
  uint64_t blob_compaction_readahead_size = 0;

  // Enable blob files starting from a certain LSM tree level.
  //
  // For certain use cases that have a mix of short-lived and long-lived values,
  // it might make sense to support extracting large values only during
  // compactions whose output level is greater than or equal to a specified LSM
  // tree level (e.g. compactions into L1/L2/... or above). This could reduce
  // the space amplification caused by large values that are turned into garbage
  // shortly after being written at the price of some write amplification
  // incurred by long-lived values whose extraction to blob files is delayed.
  //
  // Default: 0
  //
  // Dynamically changeable through the SetOptions() API
  int blob_file_starting_level = 0;

  // This feature is WORK IN PROGRESS
  // If non-NULL use the specified cache for blobs.
  // If NULL, rocksdb will not use a blob cache.
  //
  // Default: nullptr (disabled)
  std::shared_ptr<Cache> blob_cache = nullptr;

  // If enabled, prepopulate warm/hot blobs which are already in memory into
  // blob cache at the time of flush. On a flush, the blob that is in memory (in
  // memtables) get flushed to the device. If using Direct IO, additional IO is
  // incurred to read this blob back into memory again, which is avoided by
  // enabling this option. This further helps if the workload exhibits high
  // temporal locality, where most of the reads go to recently written data.
  // This also helps in case of the remote file system since it involves network
  // traffic and higher latencies.
  //
  // Default: disabled
  //
  // Dynamically changeable through the SetOptions() API
  PrepopulateBlobCache prepopulate_blob_cache = PrepopulateBlobCache::kDisable;

  // Create ColumnFamilyOptions with default values for all fields
  AdvancedColumnFamilyOptions();
  // Create ColumnFamilyOptions from Options
  explicit AdvancedColumnFamilyOptions(const Options& options);

  // ---------------- OPTIONS NOT SUPPORTED ANYMORE ----------------
};

}  // namespace ROCKSDB_NAMESPACE