rocksdb/include/leveldb/options.h
Dhruba Borthakur 5d16e503a6 Improved CompactionFilter api: pass in a opaque argument to CompactionFilter invocation.
Summary:
There are applications that operate on multiple leveldb instances.
These applications will like to pass in an opaque type for each
leveldb instance and this type should be passed back to the application
with every invocation of the CompactionFilter api.

Test Plan: Enehanced unit test for opaque parameter to CompactionFilter.

Reviewers: heyongqiang

Reviewed By: heyongqiang

CC: MarkCallaghan, sheki, emayanke

Differential Revision: https://reviews.facebook.net/D6711
2012-11-13 16:22:26 -08:00

398 lines
15 KiB
C++

// 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.
#ifndef STORAGE_LEVELDB_INCLUDE_OPTIONS_H_
#define STORAGE_LEVELDB_INCLUDE_OPTIONS_H_
#include <stddef.h>
#include <string>
#include <stdint.h>
#include "leveldb/slice.h"
namespace leveldb {
class Cache;
class Comparator;
class Env;
class FilterPolicy;
class Logger;
class Snapshot;
class Statistics;
// DB contents are stored in a set of blocks, each of which holds a
// sequence of key,value pairs. Each block may be compressed before
// being stored in a file. The following enum describes which
// compression method (if any) is used to compress a block.
enum CompressionType {
// NOTE: do not change the values of existing entries, as these are
// part of the persistent format on disk.
kNoCompression = 0x0,
kSnappyCompression = 0x1,
kZlibCompression = 0x2,
kBZip2Compression = 0x3
};
// Compression options for different compression algorithms like Zlib
struct CompressionOptions {
int window_bits;
int level;
int strategy;
CompressionOptions():window_bits(-14),
level(-1),
strategy(0){}
CompressionOptions(int wbits, int lev, int strategy):window_bits(wbits),
level(lev),
strategy(strategy){}
};
// Options to control the behavior of a database (passed to DB::Open)
struct Options {
// -------------------
// Parameters that affect behavior
// Comparator used to define the order of keys in the table.
// Default: a comparator that uses lexicographic byte-wise ordering
//
// REQUIRES: The client must ensure that the comparator supplied
// here has the same name and orders keys *exactly* the same as the
// comparator provided to previous open calls on the same DB.
const Comparator* comparator;
// If true, the database will be created if it is missing.
// Default: false
bool create_if_missing;
// If true, an error is raised if the database already exists.
// Default: false
bool error_if_exists;
// If true, the implementation will do aggressive checking of the
// data it is processing and will stop early if it detects any
// errors. This may have unforeseen ramifications: for example, a
// corruption of one DB entry may cause a large number of entries to
// become unreadable or for the entire DB to become unopenable.
// Default: false
bool paranoid_checks;
// Use the specified object to interact with the environment,
// e.g. to read/write files, schedule background work, etc.
// Default: Env::Default()
Env* env;
// Any internal progress/error information generated by the db will
// be written to info_log if it is non-NULL, or to a file stored
// in the same directory as the DB contents if info_log is NULL.
// Default: NULL
Logger* info_log;
// -------------------
// Parameters that affect performance
// Amount of data to build up in memory (backed by an unsorted log
// on disk) before converting to a sorted on-disk file.
//
// Larger values increase performance, especially during bulk loads.
// Up to two write buffers may be held in memory at the same time,
// so you may wish to adjust this parameter to control memory usage.
// Also, a larger write buffer will result in a longer recovery time
// the next time the database is opened.
//
// Default: 4MB
size_t write_buffer_size;
// Number of open files that can be used by the DB. You may need to
// increase this if your database has a large working set (budget
// one open file per 2MB of working set).
//
// Default: 1000
int max_open_files;
// Control over blocks (user data is stored in a set of blocks, and
// a block is the unit of reading from disk).
// If non-NULL, use the specified cache for blocks.
// If NULL, leveldb will automatically create and use an 8MB internal cache.
// Default: NULL
Cache* block_cache;
// Approximate size of user data packed per block. Note that the
// block size specified here corresponds to uncompressed data. The
// actual size of the unit read from disk may be smaller if
// compression is enabled. This parameter can be changed dynamically.
//
// Default: 4K
size_t block_size;
// Number of keys between restart points for delta encoding of keys.
// This parameter can be changed dynamically. Most clients should
// leave this parameter alone.
//
// Default: 16
int block_restart_interval;
// Compress blocks using the specified compression algorithm. This
// parameter can be changed dynamically.
//
// Default: kSnappyCompression, which gives lightweight but fast
// compression.
//
// Typical speeds of kSnappyCompression on an Intel(R) Core(TM)2 2.4GHz:
// ~200-500MB/s compression
// ~400-800MB/s decompression
// Note that these speeds are significantly faster than most
// persistent storage speeds, and therefore it is typically never
// worth switching to kNoCompression. Even if the input data is
// incompressible, the kSnappyCompression implementation will
// efficiently detect that and will switch to uncompressed mode.
CompressionType compression;
// Different levels can have different compression policies. There
// are cases where most lower levels would like to quick compression
// algorithm while the higher levels (which have more data) use
// compression algorithms that have better compression but could
// be slower. This array, if non NULL, should have an entry for
// each level of the database. This array, if non NULL, overides the
// value specified in the previous field 'compression'. The caller is
// reponsible for allocating memory and initializing the values in it
// before invoking Open(). The caller is responsible for freeing this
// array and it could be freed anytime after the return from Open().
// This could have been a std::vector but that makes the equivalent
// java/C api hard to construct.
CompressionType* compression_per_level;
//different options for compression algorithms
CompressionOptions compression_opts;
// If non-NULL, use the specified filter policy to reduce disk reads.
// Many applications will benefit from passing the result of
// NewBloomFilterPolicy() here.
//
// Default: NULL
const FilterPolicy* filter_policy;
// Number of levels for this database
int num_levels;
// Number of files to trigger level-0 compaction. A value <0 means that
// level-0 compaction will not be triggered by number of files at all.
int level0_file_num_compaction_trigger;
// Soft limit on number of level-0 files. We slow down writes at this point.
// A value <0 means that no writing slow down will be triggered by number
// of files in level-0.
int level0_slowdown_writes_trigger;
// Maximum number of level-0 files. We stop writes at this point.
int level0_stop_writes_trigger;
// Maximum level to which a new compacted memtable is pushed if it
// does not create overlap. We try to push to level 2 to avoid the
// relatively expensive level 0=>1 compactions and to avoid some
// expensive manifest file operations. We do not push all the way to
// the largest level since that can generate a lot of wasted disk
// space if the same key space is being repeatedly overwritten.
int max_mem_compaction_level;
// 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.
// by default target_file_size_base is 2MB.
int target_file_size_base;
// by default target_file_size_multiplier is 1, which means
// by default files in different levels will have similar size.
int target_file_size_multiplier;
// Control maximum total data size for a level.
// max_bytes_for_level_base is the max total for level-1.
// Maximum number of bytes for level L can be calculated as
// (max_bytes_for_level_base) * (max_bytes_for_level_multiplier ^ (L-1))
// For example, if max_bytes_for_level_base is 20MB, and if
// max_bytes_for_level_multiplier is 10, total data size for level-1
// will be 20MB, total file size for level-2 will be 200MB,
// and total file size for level-3 will be 2GB.
// by default 'max_bytes_for_level_base' is 10MB.
uint64_t max_bytes_for_level_base;
// by default 'max_bytes_for_level_base' is 10.
int max_bytes_for_level_multiplier;
// Maximum number of bytes in all compacted files. We avoid expanding
// the lower level file set of a compaction if it would make the
// total compaction cover more than
// (expanded_compaction_factor * targetFileSizeLevel()) many bytes.
int expanded_compaction_factor;
// Control maximum bytes of overlaps in grandparent (i.e., level+2) before we
// stop building a single file in a level->level+1 compaction.
int max_grandparent_overlap_factor;
// If non-null, then we should collect metrics about database operations
Statistics* statistics;
// If true, then the contents of data files are not synced
// to stable storage. Their contents remain in the OS buffers till the
// OS decides to flush them. This option is good for bulk-loading
// of data. Once the bulk-loading is complete, please issue a
// sync to the OS to flush all dirty buffesrs to stable storage.
// Default: false
bool disableDataSync;
// If true, then every store to stable storage will issue a fsync.
// If false, then every store to stable storage will issue a fdatasync.
// This parameter should be set to true while storing data to
// filesystem like ext3 which can lose files after a reboot.
// Default: false
bool use_fsync;
// This number controls how often a new scribe log about
// db deploy stats is written out.
// -1 indicates no logging at all.
// Default value is 1800 (half an hour).
int db_stats_log_interval;
// This specifies the log dir.
// If it is empty, the log files will be in the same dir as data.
// If it is non empty, the log files will be in the specified dir,
// and the db data dir's absolute path will be used as the log file
// name's prefix.
std::string db_log_dir;
// Disable compaction triggered by seek.
// With bloomfilter and fast storage, a miss on one level
// is very cheap if the file handle is cached in table cache
// (which is true if max_open_files is large).
bool disable_seek_compaction;
// The periodicity when obsolete files get deleted. The default
// value is 0 which means that obsolete files get removed after
// every compaction run.
uint64_t delete_obsolete_files_period_micros;
// Specify the maximal size of the info log file. If the log file
// is larger than `max_log_file_size`, a new info log file will
// be created.
// If max_log_file_size == 0, all logs will be written to one
// log file.
size_t max_log_file_size;
// Puts are delayed when any level has a compaction score that
// exceeds rate_limit. This is ignored when <= 1.0.
double rate_limit;
// Disable block cache. If this is set to false,
// then no block cache should be used, and the block_cache should
// point to a NULL object.
bool no_block_cache;
// Number of shards used for table cache.
int table_cache_numshardbits;
// Create an Options object with default values for all fields.
Options();
void Dump(Logger * log) const;
// This method allows an application to modify/delete a key-value at
// the time of compaction. The compaction process invokes this
// method for every kv that is being compacted. A return value
// of false indicates that the kv should be preserved in the
// output of this compaction run and a return value of true
// indicates that this key-value should be removed from the
// output of the compaction. The application can inspect
// the existing value of the key, modify it if needed and
// return back the new value for this key. The application
// should allocate memory for the Slice object that is used to
// return the new value and the leveldb framework will
// free up that memory.
// The compaction_filter_args, if specified here, are passed
// back to the invocation of the CompactionFilter.
void* compaction_filter_args;
bool (*CompactionFilter)(void* compaction_filter_args,
int level, const Slice& key,
const Slice& existing_value, Slice** new_value);
};
// Options that control read operations
struct ReadOptions {
// If true, all data read from underlying storage will be
// verified against corresponding checksums.
// Default: false
bool verify_checksums;
// Should the data read for this iteration be cached in memory?
// Callers may wish to set this field to false for bulk scans.
// Default: true
bool fill_cache;
// If "snapshot" is non-NULL, read as of the supplied snapshot
// (which must belong to the DB that is being read and which must
// not have been released). If "snapshot" is NULL, use an impliicit
// snapshot of the state at the beginning of this read operation.
// Default: NULL
const Snapshot* snapshot;
ReadOptions()
: verify_checksums(false),
fill_cache(true),
snapshot(NULL) {
}
ReadOptions(bool cksum, bool cache) :
verify_checksums(cksum), fill_cache(cache),
snapshot(NULL) {
}
};
// Options that control write operations
struct WriteOptions {
// If true, the write will be flushed from the operating system
// buffer cache (by calling WritableFile::Sync()) before the write
// is considered complete. If this flag is true, writes will be
// slower.
//
// If this flag is false, and the machine crashes, some recent
// writes may be lost. Note that if it is just the process that
// crashes (i.e., the machine does not reboot), no writes will be
// lost even if sync==false.
//
// In other words, a DB write with sync==false has similar
// crash semantics as the "write()" system call. A DB write
// with sync==true has similar crash semantics to a "write()"
// system call followed by "fsync()".
//
// Default: false
bool sync;
// If true, writes will not first go to the write ahead log,
// and the write may got lost after a crash.
bool disableWAL;
WriteOptions()
: sync(false),
disableWAL(false) {
}
};
// Options that control flush operations
struct FlushOptions {
// If true, the flush will wait until the flush is done.
// Default: true
bool wait;
FlushOptions()
: wait(true) {
}
};
} // namespace leveldb
#endif // STORAGE_LEVELDB_INCLUDE_OPTIONS_H_