Try TerarkDB With Full Features

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Try TerarkDB With Full Features

Now you have compiled terark rocksdb and downloaded terark-zip-rocksdb, if not, see here...

1. Introduction

2. Who Need This

• People who need more granular control on SSTable (Requires code changes in your application).
• People who want to know more details about TerarkZipTable (Our implementation of SSTable).

NOTE: If you just want to experience TerarkDB without code changes of your application, please refer to Quick Start

3. RocksDB utility tools for TerarkDB

In this RocksDB fork, we add some extra options to use TerarkDB, e.g.:

Utility	TerarkDB option
ldb	--use_terarkdb=1

4. TerarkDB Restrictions

• User comparator is not supported, you should encode your keys byte lexical order
• EnvOptions::use_mmap_reads must be true, can be set by DBOptions::allow_mmap_reads

5. RocksdDB Cautions & Notes

• table_factory is a member of ColumnFamilyOptions, not DBOptions!
• If calling rocksdb::DB::Open() with column families, you must set table_factory for each ColumnFamilyDescriptor

// Caution: When calling this `Open` overload, you must 
// set column_families[i].options.table_factory
//
// You may pass an rocksdb::Option object as db_options, but this
// db_options.table_factory will NOT be used!!
//
static Status Open(const DBOptions& db_options, const std::string& name,
                   const std::vector<ColumnFamilyDescriptor>& column_families,
                   std::vector<ColumnFamilyHandle*>* handles, DB** dbptr);

6. Using TerarkZipTable

6.1. Now just for C++

• Compile flags

CXXFLAGS += -I/path/to/terark-zip-rocksdb/src

• Linker flags

LDFLAGS += -L/path/to/terark-zip-rocksdb-lib
LDFLAGS += -lterark-zip-rocksdb-r
LDFLAGS += -lterark-zbs-r -lterark-fsa-r -lterark-core-r

• C++ code

#include <table/terark_zip_table.h>
/// other includes...

  ///....
  TerarkZipTableOptions opt;

  /// TerarkZipTable needs to create temp files during compression
  opt.localTempDir = "/path/to/some/temp/dir"; // default is "/tmp"

  /// 0 : check sum nothing
  /// 1 : check sum meta data and index, check on file load
  /// 2 : check sum all data, not check on file load, checksum is for
  ///     each record, this incurs 4 bytes overhead for each record
  /// 3 : check sum all data with one checksum value, not checksum each record,
  ///     if checksum doesn't match, load will fail
  opt.checksumLevel = 3; // default 1

  ///    < 0 : only last level using terarkZip
  ///          this is equivalent to terarkZipMinLevel == num_levels-1
  /// others : use terarkZip when curlevel >= terarkZipMinLevel
  ///          this includes the two special cases:
  ///                   == 0 : all levels using terarkZip
  ///          >= num_levels : all levels using fallback TableFactory
  /// it shown that set terarkZipMinLevel = 0 is the best choice
  /// if mixed with rocksdb's native SST, those SSTs may using too much
  /// memory & SSD, which degrades the performance
  opt.terarkZipMinLevel = 0; // default

  /// optional
  opt.softZipWorkingMemLimit = 16ull << 30; // default
  opt.hardZipWorkingMemLimit = 32ull << 30; // default

  /// to let rocksdb compaction algo know the estimate SST file size
  opt.estimateCompressionRatio = 0.2;

  /// the global dictionary size over all value size
  opt.sampleRatio = 0.03;
 
  /// other opt are tricky, just use default

  /// rocksdb options when using terark-zip-rocksdb:

  /// fallback can be NULL
  auto fallback = NewBlockBasedTableFactory(); // or NewAdaptiveTableFactory();
  auto factory = NewTerarkZipTableFactory(opt, fallback);
  options.table_factory.reset(factory);

  /// terark-zip use mmap
  options.allow_mmap_reads = true;

  /// universal compaction reduce write amplification and is more friendly for
  /// large SST file, terark SST is better on larger SST file.
  /// although universal compaction needs 2x SSD space on worst case, but
  /// with terark-zip's high compression, the used SSD space is much smaller
  /// than rocksdb's block compression schema
  options.compaction_style = rocksdb::kCompactionStyleUniversal;

  /// larger MemTable yield larger level0 SST file
  /// larger SST file make terark-zip better
  options.write_buffer_size     =  1ull << 30; // 1G
  options.target_file_size_base =  1ull << 30; // 1G

  /// single sst file size on greater levels should be larger
  /// filesize(level[n+1]) = filesize(level[n]) * target_file_size_multiplier
  options.target_file_size_multiplier = 2; // can be larger, such as 3,5,10

  /// turn off rocksdb write slowdown, optional. If write slowdown is enabled
  /// and write was really slow down, you may doubt that terark-zip caused it
  options.level0_slowdown_writes_trigger = INT_MAX;
  options.level0_stop_writes_trigger = INT_MAX;
  options.soft_pending_compaction_bytes_limit = 0;
  options.hard_pending_compaction_bytes_limit = 0;