175 lines
6.6 KiB
Go
175 lines
6.6 KiB
Go
/*
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* Copyright 2017 Dgraph Labs, Inc. and Contributors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package badger
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import (
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"github.com/dgraph-io/badger/options"
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)
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// NOTE: Keep the comments in the following to 75 chars width, so they
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// format nicely in godoc.
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// Options are params for creating DB object.
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//
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// This package provides DefaultOptions which contains options that should
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// work for most applications. Consider using that as a starting point before
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// customizing it for your own needs.
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type Options struct {
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// 1. Mandatory flags
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// -------------------
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// Directory to store the data in. If it doesn't exist, Badger will
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// try to create it for you.
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Dir string
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// Directory to store the value log in. Can be the same as Dir. If it
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// doesn't exist, Badger will try to create it for you.
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ValueDir string
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// 2. Frequently modified flags
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// -----------------------------
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// Sync all writes to disk. Setting this to false would achieve better
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// performance, but may cause data to be lost.
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SyncWrites bool
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// How should LSM tree be accessed.
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TableLoadingMode options.FileLoadingMode
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// How should value log be accessed.
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ValueLogLoadingMode options.FileLoadingMode
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// How many versions to keep per key.
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NumVersionsToKeep int
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// Open the DB as read-only. With this set, multiple processes can
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// open the same Badger DB. Note: if the DB being opened had crashed
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// before and has vlog data to be replayed, ReadOnly will cause Open
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// to fail with an appropriate message.
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ReadOnly bool
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// Truncate value log to delete corrupt data, if any. Would not truncate if ReadOnly is set.
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Truncate bool
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// DB-specific logger which will override the global logger.
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Logger Logger
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// 3. Flags that user might want to review
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// ----------------------------------------
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// The following affect all levels of LSM tree.
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MaxTableSize int64 // Each table (or file) is at most this size.
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LevelSizeMultiplier int // Equals SizeOf(Li+1)/SizeOf(Li).
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MaxLevels int // Maximum number of levels of compaction.
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// If value size >= this threshold, only store value offsets in tree.
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ValueThreshold int
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// Maximum number of tables to keep in memory, before stalling.
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NumMemtables int
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// The following affect how we handle LSM tree L0.
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// Maximum number of Level 0 tables before we start compacting.
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NumLevelZeroTables int
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// If we hit this number of Level 0 tables, we will stall until L0 is
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// compacted away.
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NumLevelZeroTablesStall int
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// Maximum total size for L1.
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LevelOneSize int64
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// Size of single value log file.
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ValueLogFileSize int64
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// Max number of entries a value log file can hold (approximately). A value log file would be
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// determined by the smaller of its file size and max entries.
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ValueLogMaxEntries uint32
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// Number of compaction workers to run concurrently. Setting this to zero would stop compactions
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// to happen within LSM tree. If set to zero, writes could block forever.
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NumCompactors int
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// When closing the DB, force compact Level 0. This ensures that both reads and writes are
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// efficient when the DB is opened later.
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CompactL0OnClose bool
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// After this many number of value log file rotates, there would be a force flushing of memtable
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// to disk. This is useful in write loads with fewer keys and larger values. This work load
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// would fill up the value logs quickly, while not filling up the Memtables. Thus, on a crash
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// and restart, the value log head could cause the replay of a good number of value log files
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// which can slow things on start.
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LogRotatesToFlush int32
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// Transaction start and commit timestamps are managed by end-user.
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// This is only useful for databases built on top of Badger (like Dgraph).
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// Not recommended for most users.
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managedTxns bool
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// 4. Flags for testing purposes
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// ------------------------------
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maxBatchCount int64 // max entries in batch
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maxBatchSize int64 // max batch size in bytes
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}
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// DefaultOptions sets a list of recommended options for good performance.
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// Feel free to modify these to suit your needs.
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var DefaultOptions = Options{
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LevelOneSize: 256 << 20,
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LevelSizeMultiplier: 10,
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TableLoadingMode: options.MemoryMap,
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ValueLogLoadingMode: options.MemoryMap,
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// table.MemoryMap to mmap() the tables.
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// table.Nothing to not preload the tables.
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MaxLevels: 7,
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MaxTableSize: 64 << 20,
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NumCompactors: 2, // Compactions can be expensive. Only run 2.
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NumLevelZeroTables: 5,
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NumLevelZeroTablesStall: 10,
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NumMemtables: 5,
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SyncWrites: true,
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NumVersionsToKeep: 1,
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CompactL0OnClose: true,
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// Nothing to read/write value log using standard File I/O
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// MemoryMap to mmap() the value log files
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// (2^30 - 1)*2 when mmapping < 2^31 - 1, max int32.
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// -1 so 2*ValueLogFileSize won't overflow on 32-bit systems.
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ValueLogFileSize: 1<<30 - 1,
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ValueLogMaxEntries: 1000000,
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ValueThreshold: 32,
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Truncate: false,
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Logger: defaultLogger,
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LogRotatesToFlush: 2,
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}
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// LSMOnlyOptions follows from DefaultOptions, but sets a higher ValueThreshold
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// so values would be colocated with the LSM tree, with value log largely acting
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// as a write-ahead log only. These options would reduce the disk usage of value
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// log, and make Badger act more like a typical LSM tree.
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var LSMOnlyOptions = Options{}
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func init() {
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LSMOnlyOptions = DefaultOptions
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LSMOnlyOptions.ValueThreshold = 65500 // Max value length which fits in uint16.
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// Let's not set any other options, because they can cause issues with the
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// size of key-value a user can pass to Badger. For e.g., if we set
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// ValueLogFileSize to 64MB, a user can't pass a value more than that.
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// Setting it to ValueLogMaxEntries to 1000, can generate too many files.
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// These options are better configured on a usage basis, than broadly here.
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// The ValueThreshold is the most important setting a user needs to do to
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// achieve a heavier usage of LSM tree.
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// NOTE: If a user does not want to set 64KB as the ValueThreshold because
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// of performance reasons, 1KB would be a good option too, allowing
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// values smaller than 1KB to be colocated with the keys in the LSM tree.
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}
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