You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
 
 
 
 
 
 
rocksdb/include/leveldb/options.h

499 lines
19 KiB

// 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 <memory>
#include <vector>
#include <stdint.h>
#include "leveldb/slice.h"
#include "leveldb/statistics.h"
namespace leveldb {
class Cache;
class Comparator;
class Env;
class FilterPolicy;
class Logger;
class Snapshot;
using std::shared_ptr;
// 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-nullptr, or to a file stored
// in the same directory as the DB contents if info_log is nullptr.
// Default: nullptr
shared_ptr<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 max_write_buffer_number 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;
// The maximum number of write buffers that are built up in memory.
// The default is 2, so that when 1 write buffer is being flushed to
// storage, new writes can continue to the other write buffer.
// Default: 2
int max_write_buffer_number;
// 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: nullptr
shared_ptr<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 nullptr, should have an entry for
// each level of the database. This array, if non nullptr, 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.
std::vector<CompressionType> compression_per_level;
//different options for compression algorithms
CompressionOptions compression_opts;
// If non-nullptr, use the specified filter policy to reduce disk reads.
// Many applications will benefit from passing the result of
// NewBloomFilterPolicy() here.
//
// Default: nullptr
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;
// Maximum number of bytes in all source files to be compacted in a
// single compaction run. We avoid picking too many files in the
// source level so that we do not exceed the total source bytes
// for compaction to exceed
// (source_compaction_factor * targetFileSizeLevel()) many bytes.
// Default:1, i.e. pick maxfilesize amount of data as the source of
// a compaction.
int source_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 objects should not be shared between DB instances as
// it does not use any locks to prevent concurrent updates.
shared_ptr<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;
// Maximum number of concurrent background compactions.
// Default: 1
int max_background_compactions;
// 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;
// Time for the info log file to roll (in seconds).
// If specified with non-zero value, log file will be rolled
// if it has been active longer than `log_file_time_to_roll`.
// Default: 0 (disabled)
size_t log_file_time_to_roll;
// Maximal info log files to be kept.
// Default: 1000
size_t keep_log_file_num;
// Puts are delayed when any level has a compaction score that
// exceeds rate_limit. This is ignored when <= 1.0.
double rate_limit;
// Max time a put will be stalled when rate_limit is enforced
unsigned int rate_limit_delay_milliseconds;
// manifest file is rolled over on reaching this limit.
// The older manifest file be deleted.
// The default value is MAX_INT so that roll-over does not take place.
uint64_t max_manifest_file_size;
// Disable block cache. If this is set to false,
// then no block cache should be used, and the block_cache should
// point to a nullptr 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;
// Set appropriate parameters for bulk loading.
// The reason that this is a function that returns "this" instead of a
// constructor is to enable chaining of multiple similar calls in the future.
//
// All data will be in level 0 without any automatic compaction.
// It's recommended to manually call CompactRange(NULL, NULL) before reading
// from the database, because otherwise the read can be very slow.
Options* PrepareForBulkLoad();
// This method allows an application to modify/delete a key-value at
// the time of compaction. The compaction process invokes this
// method for 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 and make decision based on it.
// When the value is to be preserved, the application has the option
// to modify the existing_value and pass it back through new_value.
// value_changed needs to be set to true in this case.
// 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,
std::string* new_value,
bool* value_changed);
// Disable automatic compactions. Manual compactions can still
// be issued on this database.
bool disable_auto_compactions;
// The number of seconds a WAL(write ahead log) should be kept after it has
// been marked as Not Live. If the value is set. The WAL files are moved to
// the archive direcotory and deleted after the given TTL.
// If set to 0, WAL files are deleted as soon as they are not required by
// the database.
// If set to std::numeric_limits<uint64_t>::max() the WAL files will never be
// deleted.
// Default : 0
uint64_t WAL_ttl_seconds;
// Number of bytes to preallocate (via fallocate) the manifest
// files. Default is 4mb, which is reasonable to reduce random IO
// as well as prevent overallocation for mounts that preallocate
// large amounts of data (such as xfs's allocsize option).
size_t manifest_preallocation_size;
// Purge duplicate/deleted keys when a memtable is flushed to storage.
// Default: true
bool purge_redundant_kvs_while_flush;
// Data being read from file storage may be buffered in the OS
// Default: true
bool allow_os_buffer;
// Reading a single block from a file can cause the OS/FS to start
// readaheads of other blocks from the file. Default: true
bool allow_readahead;
// The reads triggered by compaction allows data to be readahead
// by the OS/FS. This overrides the setting of 'allow_readahead'
// for compaction-reads. Default: true
bool allow_readahead_compactions;
// Allow the OS to mmap file for reading. Default: false
bool allow_mmap_reads;
// Allow the OS to mmap file for writing. Default: true
bool allow_mmap_writes;
// Disable child process inherit open files. Default: true
bool is_fd_close_on_exec;
};
// 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-nullptr, 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 nullptr, use an impliicit
// snapshot of the state at the beginning of this read operation.
// Default: nullptr
const Snapshot* snapshot;
ReadOptions()
: verify_checksums(false),
fill_cache(true),
snapshot(nullptr) {
}
ReadOptions(bool cksum, bool cache) :
verify_checksums(cksum), fill_cache(cache),
snapshot(nullptr) {
}
};
// 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_