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diff --git a/cmd/ponzu/vendor/github.com/boltdb/bolt b/cmd/ponzu/vendor/github.com/boltdb/bolt deleted file mode 160000 -Subproject 074dffcc83e9f421e261526d297cd93f22a3408 diff --git a/cmd/ponzu/vendor/github.com/boltdb/bolt/README.md b/cmd/ponzu/vendor/github.com/boltdb/bolt/README.md new file mode 100644 index 0000000..b654502 --- /dev/null +++ b/cmd/ponzu/vendor/github.com/boltdb/bolt/README.md @@ -0,0 +1,858 @@ +Bolt [](https://coveralls.io/r/boltdb/bolt?branch=master) [](https://godoc.org/github.com/boltdb/bolt)  +==== + +Bolt is a pure Go key/value store inspired by [Howard Chu's][hyc_symas] +[LMDB project][lmdb]. The goal of the project is to provide a simple, +fast, and reliable database for projects that don't require a full database +server such as Postgres or MySQL. + +Since Bolt is meant to be used as such a low-level piece of functionality, +simplicity is key. The API will be small and only focus on getting values +and setting values. That's it. + +[hyc_symas]: https://twitter.com/hyc_symas +[lmdb]: http://symas.com/mdb/ + +## Project Status + +Bolt is stable, the API is fixed, and the file format is fixed. Full unit +test coverage and randomized black box testing are used to ensure database +consistency and thread safety. Bolt is currently used in high-load production +environments serving databases as large as 1TB. Many companies such as +Shopify and Heroku use Bolt-backed services every day. + +## Table of Contents + +- [Getting Started](#getting-started) + - [Installing](#installing) + - [Opening a database](#opening-a-database) + - [Transactions](#transactions) + - [Read-write transactions](#read-write-transactions) + - [Read-only transactions](#read-only-transactions) + - [Batch read-write transactions](#batch-read-write-transactions) + - [Managing transactions manually](#managing-transactions-manually) + - [Using buckets](#using-buckets) + - [Using key/value pairs](#using-keyvalue-pairs) + - [Autoincrementing integer for the bucket](#autoincrementing-integer-for-the-bucket) + - [Iterating over keys](#iterating-over-keys) + - [Prefix scans](#prefix-scans) + - [Range scans](#range-scans) + - [ForEach()](#foreach) + - [Nested buckets](#nested-buckets) + - [Database backups](#database-backups) + - [Statistics](#statistics) + - [Read-Only Mode](#read-only-mode) + - [Mobile Use (iOS/Android)](#mobile-use-iosandroid) +- [Resources](#resources) +- [Comparison with other databases](#comparison-with-other-databases) + - [Postgres, MySQL, & other relational databases](#postgres-mysql--other-relational-databases) + - [LevelDB, RocksDB](#leveldb-rocksdb) + - [LMDB](#lmdb) +- [Caveats & Limitations](#caveats--limitations) +- [Reading the Source](#reading-the-source) +- [Other Projects Using Bolt](#other-projects-using-bolt) + +## Getting Started + +### Installing + +To start using Bolt, install Go and run `go get`: + +```sh +$ go get github.com/boltdb/bolt/... +``` + +This will retrieve the library and install the `bolt` command line utility into +your `$GOBIN` path. + + +### Opening a database + +The top-level object in Bolt is a `DB`. It is represented as a single file on +your disk and represents a consistent snapshot of your data. + +To open your database, simply use the `bolt.Open()` function: + +```go +package main + +import ( + "log" + + "github.com/boltdb/bolt" +) + +func main() { + // Open the my.db data file in your current directory. + // It will be created if it doesn't exist. + db, err := bolt.Open("my.db", 0600, nil) + if err != nil { + log.Fatal(err) + } + defer db.Close() + + ... +} +``` + +Please note that Bolt obtains a file lock on the data file so multiple processes +cannot open the same database at the same time. Opening an already open Bolt +database will cause it to hang until the other process closes it. To prevent +an indefinite wait you can pass a timeout option to the `Open()` function: + +```go +db, err := bolt.Open("my.db", 0600, &bolt.Options{Timeout: 1 * time.Second}) +``` + + +### Transactions + +Bolt allows only one read-write transaction at a time but allows as many +read-only transactions as you want at a time. Each transaction has a consistent +view of the data as it existed when the transaction started. + +Individual transactions and all objects created from them (e.g. buckets, keys) +are not thread safe. To work with data in multiple goroutines you must start +a transaction for each one or use locking to ensure only one goroutine accesses +a transaction at a time. Creating transaction from the `DB` is thread safe. + +Read-only transactions and read-write transactions should not depend on one +another and generally shouldn't be opened simultaneously in the same goroutine. +This can cause a deadlock as the read-write transaction needs to periodically +re-map the data file but it cannot do so while a read-only transaction is open. + + +#### Read-write transactions + +To start a read-write transaction, you can use the `DB.Update()` function: + +```go +err := db.Update(func(tx *bolt.Tx) error { + ... + return nil +}) +``` + +Inside the closure, you have a consistent view of the database. You commit the +transaction by returning `nil` at the end. You can also rollback the transaction +at any point by returning an error. All database operations are allowed inside +a read-write transaction. + +Always check the return error as it will report any disk failures that can cause +your transaction to not complete. If you return an error within your closure +it will be passed through. + + +#### Read-only transactions + +To start a read-only transaction, you can use the `DB.View()` function: + +```go +err := db.View(func(tx *bolt.Tx) error { + ... + return nil +}) +``` + +You also get a consistent view of the database within this closure, however, +no mutating operations are allowed within a read-only transaction. You can only +retrieve buckets, retrieve values, and copy the database within a read-only +transaction. + + +#### Batch read-write transactions + +Each `DB.Update()` waits for disk to commit the writes. This overhead +can be minimized by combining multiple updates with the `DB.Batch()` +function: + +```go +err := db.Batch(func(tx *bolt.Tx) error { + ... + return nil +}) +``` + +Concurrent Batch calls are opportunistically combined into larger +transactions. Batch is only useful when there are multiple goroutines +calling it. + +The trade-off is that `Batch` can call the given +function multiple times, if parts of the transaction fail. The +function must be idempotent and side effects must take effect only +after a successful return from `DB.Batch()`. + +For example: don't display messages from inside the function, instead +set variables in the enclosing scope: + +```go +var id uint64 +err := db.Batch(func(tx *bolt.Tx) error { + // Find last key in bucket, decode as bigendian uint64, increment + // by one, encode back to []byte, and add new key. + ... + id = newValue + return nil +}) +if err != nil { + return ... +} +fmt.Println("Allocated ID %d", id) +``` + + +#### Managing transactions manually + +The `DB.View()` and `DB.Update()` functions are wrappers around the `DB.Begin()` +function. These helper functions will start the transaction, execute a function, +and then safely close your transaction if an error is returned. This is the +recommended way to use Bolt transactions. + +However, sometimes you may want to manually start and end your transactions. +You can use the `DB.Begin()` function directly but **please** be sure to close +the transaction. + +```go +// Start a writable transaction. +tx, err := db.Begin(true) +if err != nil { + return err +} +defer tx.Rollback() + +// Use the transaction... +_, err := tx.CreateBucket([]byte("MyBucket")) +if err != nil { + return err +} + +// Commit the transaction and check for error. +if err := tx.Commit(); err != nil { + return err +} +``` + +The first argument to `DB.Begin()` is a boolean stating if the transaction +should be writable. + + +### Using buckets + +Buckets are collections of key/value pairs within the database. All keys in a +bucket must be unique. You can create a bucket using the `DB.CreateBucket()` +function: + +```go +db.Update(func(tx *bolt.Tx) error { + b, err := tx.CreateBucket([]byte("MyBucket")) + if err != nil { + return fmt.Errorf("create bucket: %s", err) + } + return nil +}) +``` + +You can also create a bucket only if it doesn't exist by using the +`Tx.CreateBucketIfNotExists()` function. It's a common pattern to call this +function for all your top-level buckets after you open your database so you can +guarantee that they exist for future transactions. + +To delete a bucket, simply call the `Tx.DeleteBucket()` function. + + +### Using key/value pairs + +To save a key/value pair to a bucket, use the `Bucket.Put()` function: + +```go +db.Update(func(tx *bolt.Tx) error { + b := tx.Bucket([]byte("MyBucket")) + err := b.Put([]byte("answer"), []byte("42")) + return err +}) +``` + +This will set the value of the `"answer"` key to `"42"` in the `MyBucket` +bucket. To retrieve this value, we can use the `Bucket.Get()` function: + +```go +db.View(func(tx *bolt.Tx) error { + b := tx.Bucket([]byte("MyBucket")) + v := b.Get([]byte("answer")) + fmt.Printf("The answer is: %s\n", v) + return nil +}) +``` + +The `Get()` function does not return an error because its operation is +guaranteed to work (unless there is some kind of system failure). If the key +exists then it will return its byte slice value. If it doesn't exist then it +will return `nil`. It's important to note that you can have a zero-length value +set to a key which is different than the key not existing. + +Use the `Bucket.Delete()` function to delete a key from the bucket. + +Please note that values returned from `Get()` are only valid while the +transaction is open. If you need to use a value outside of the transaction +then you must use `copy()` to copy it to another byte slice. + + +### Autoincrementing integer for the bucket +By using the `NextSequence()` function, you can let Bolt determine a sequence +which can be used as the unique identifier for your key/value pairs. See the +example below. + +```go +// CreateUser saves u to the store. The new user ID is set on u once the data is persisted. +func (s *Store) CreateUser(u *User) error { + return s.db.Update(func(tx *bolt.Tx) error { + // Retrieve the users bucket. + // This should be created when the DB is first opened. + b := tx.Bucket([]byte("users")) + + // Generate ID for the user. + // This returns an error only if the Tx is closed or not writeable. + // That can't happen in an Update() call so I ignore the error check. + id, _ := b.NextSequence() + u.ID = int(id) + + // Marshal user data into bytes. + buf, err := json.Marshal(u) + if err != nil { + return err + } + + // Persist bytes to users bucket. + return b.Put(itob(u.ID), buf) + }) +} + +// itob returns an 8-byte big endian representation of v. +func itob(v int) []byte { + b := make([]byte, 8) + binary.BigEndian.PutUint64(b, uint64(v)) + return b +} + +type User struct { + ID int + ... +} +``` + +### Iterating over keys + +Bolt stores its keys in byte-sorted order within a bucket. This makes sequential +iteration over these keys extremely fast. To iterate over keys we'll use a +`Cursor`: + +```go +db.View(func(tx *bolt.Tx) error { + // Assume bucket exists and has keys + b := tx.Bucket([]byte("MyBucket")) + + c := b.Cursor() + + for k, v := c.First(); k != nil; k, v = c.Next() { + fmt.Printf("key=%s, value=%s\n", k, v) + } + + return nil +}) +``` + +The cursor allows you to move to a specific point in the list of keys and move +forward or backward through the keys one at a time. + +The following functions are available on the cursor: + +``` +First() Move to the first key. +Last() Move to the last key. +Seek() Move to a specific key. +Next() Move to the next key. +Prev() Move to the previous key. +``` + +Each of those functions has a return signature of `(key []byte, value []byte)`. +When you have iterated to the end of the cursor then `Next()` will return a +`nil` key. You must seek to a position using `First()`, `Last()`, or `Seek()` +before calling `Next()` or `Prev()`. If you do not seek to a position then +these functions will return a `nil` key. + +During iteration, if the key is non-`nil` but the value is `nil`, that means +the key refers to a bucket rather than a value. Use `Bucket.Bucket()` to +access the sub-bucket. + + +#### Prefix scans + +To iterate over a key prefix, you can combine `Seek()` and `bytes.HasPrefix()`: + +```go +db.View(func(tx *bolt.Tx) error { + // Assume bucket exists and has keys + c := tx.Bucket([]byte("MyBucket")).Cursor() + + prefix := []byte("1234") + for k, v := c.Seek(prefix); bytes.HasPrefix(k, prefix); k, v = c.Next() { + fmt.Printf("key=%s, value=%s\n", k, v) + } + + return nil +}) +``` + +#### Range scans + +Another common use case is scanning over a range such as a time range. If you +use a sortable time encoding such as RFC3339 then you can query a specific +date range like this: + +```go +db.View(func(tx *bolt.Tx) error { + // Assume our events bucket exists and has RFC3339 encoded time keys. + c := tx.Bucket([]byte("Events")).Cursor() + + // Our time range spans the 90's decade. + min := []byte("1990-01-01T00:00:00Z") + max := []byte("2000-01-01T00:00:00Z") + + // Iterate over the 90's. + for k, v := c.Seek(min); k != nil && bytes.Compare(k, max) <= 0; k, v = c.Next() { + fmt.Printf("%s: %s\n", k, v) + } + + return nil +}) +``` + +Note that, while RFC3339 is sortable, the Golang implementation of RFC3339Nano does not use a fixed number of digits after the decimal point and is therefore not sortable. + + +#### ForEach() + +You can also use the function `ForEach()` if you know you'll be iterating over +all the keys in a bucket: + +```go +db.View(func(tx *bolt.Tx) error { + // Assume bucket exists and has keys + b := tx.Bucket([]byte("MyBucket")) + + b.ForEach(func(k, v []byte) error { + fmt.Printf("key=%s, value=%s\n", k, v) + return nil + }) + return nil +}) +``` + +Please note that keys and values in `ForEach()` are only valid while +the transaction is open. If you need to use a key or value outside of +the transaction, you must use `copy()` to copy it to another byte +slice. + +### Nested buckets + +You can also store a bucket in a key to create nested buckets. The API is the +same as the bucket management API on the `DB` object: + +```go +func (*Bucket) CreateBucket(key []byte) (*Bucket, error) +func (*Bucket) CreateBucketIfNotExists(key []byte) (*Bucket, error) +func (*Bucket) DeleteBucket(key []byte) error +``` + + +### Database backups + +Bolt is a single file so it's easy to backup. You can use the `Tx.WriteTo()` +function to write a consistent view of the database to a writer. If you call +this from a read-only transaction, it will perform a hot backup and not block +your other database reads and writes. + +By default, it will use a regular file handle which will utilize the operating +system's page cache. See the [`Tx`](https://godoc.org/github.com/boltdb/bolt#Tx) +documentation for information about optimizing for larger-than-RAM datasets. + +One common use case is to backup over HTTP so you can use tools like `cURL` to +do database backups: + +```go +func BackupHandleFunc(w http.ResponseWriter, req *http.Request) { + err := db.View(func(tx *bolt.Tx) error { + w.Header().Set("Content-Type", "application/octet-stream") + w.Header().Set("Content-Disposition", `attachment; filename="my.db"`) + w.Header().Set("Content-Length", strconv.Itoa(int(tx.Size()))) + _, err := tx.WriteTo(w) + return err + }) + if err != nil { + http.Error(w, err.Error(), http.StatusInternalServerError) + } +} +``` + +Then you can backup using this command: + +```sh +$ curl http://localhost/backup > my.db +``` + +Or you can open your browser to `http://localhost/backup` and it will download +automatically. + +If you want to backup to another file you can use the `Tx.CopyFile()` helper +function. + + +### Statistics + +The database keeps a running count of many of the internal operations it +performs so you can better understand what's going on. By grabbing a snapshot +of these stats at two points in time we can see what operations were performed +in that time range. + +For example, we could start a goroutine to log stats every 10 seconds: + +```go +go func() { + // Grab the initial stats. + prev := db.Stats() + + for { + // Wait for 10s. + time.Sleep(10 * time.Second) + + // Grab the current stats and diff them. + stats := db.Stats() + diff := stats.Sub(&prev) + + // Encode stats to JSON and print to STDERR. + json.NewEncoder(os.Stderr).Encode(diff) + + // Save stats for the next loop. + prev = stats + } +}() +``` + +It's also useful to pipe these stats to a service such as statsd for monitoring +or to provide an HTTP endpoint that will perform a fixed-length sample. + + +### Read-Only Mode + +Sometimes it is useful to create a shared, read-only Bolt database. To this, +set the `Options.ReadOnly` flag when opening your database. Read-only mode +uses a shared lock to allow multiple processes to read from the database but +it will block any processes from opening the database in read-write mode. + +```go +db, err := bolt.Open("my.db", 0666, &bolt.Options{ReadOnly: true}) +if err != nil { + log.Fatal(err) +} +``` + +### Mobile Use (iOS/Android) + +Bolt is able to run on mobile devices by leveraging the binding feature of the +[gomobile](https://github.com/golang/mobile) tool. Create a struct that will +contain your database logic and a reference to a `*bolt.DB` with a initializing +constructor that takes in a filepath where the database file will be stored. +Neither Android nor iOS require extra permissions or cleanup from using this method. + +```go +func NewBoltDB(filepath string) *BoltDB { + db, err := bolt.Open(filepath+"/demo.db", 0600, nil) + if err != nil { + log.Fatal(err) + } + + return &BoltDB{db} +} + +type BoltDB struct { + db *bolt.DB + ... +} + +func (b *BoltDB) Path() string { + return b.db.Path() +} + +func (b *BoltDB) Close() { + b.db.Close() +} +``` + +Database logic should be defined as methods on this wrapper struct. + +To initialize this struct from the native language (both platforms now sync +their local storage to the cloud. These snippets disable that functionality for the +database file): + +#### Android + +```java +String path; +if (android.os.Build.VERSION.SDK_INT >=android.os.Build.VERSION_CODES.LOLLIPOP){ + path = getNoBackupFilesDir().getAbsolutePath(); +} else{ + path = getFilesDir().getAbsolutePath(); +} +Boltmobiledemo.BoltDB boltDB = Boltmobiledemo.NewBoltDB(path) +``` + +#### iOS + +```objc +- (void)demo { + NSString* path = [NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, + NSUserDomainMask, + YES) objectAtIndex:0]; + GoBoltmobiledemoBoltDB * demo = GoBoltmobiledemoNewBoltDB(path); + [self addSkipBackupAttributeToItemAtPath:demo.path]; + //Some DB Logic would go here + [demo close]; +} + +- (BOOL)addSkipBackupAttributeToItemAtPath:(NSString *) filePathString +{ + NSURL* URL= [NSURL fileURLWithPath: filePathString]; + assert([[NSFileManager defaultManager] fileExistsAtPath: [URL path]]); + + NSError *error = nil; + BOOL success = [URL setResourceValue: [NSNumber numberWithBool: YES] + forKey: NSURLIsExcludedFromBackupKey error: &error]; + if(!success){ + NSLog(@"Error excluding %@ from backup %@", [URL lastPathComponent], error); + } + return success; +} + +``` + +## Resources + +For more information on getting started with Bolt, check out the following articles: + +* [Intro to BoltDB: Painless Performant Persistence](http://npf.io/2014/07/intro-to-boltdb-painless-performant-persistence/) by [Nate Finch](https://github.com/natefinch). +* [Bolt -- an embedded key/value database for Go](https://www.progville.com/go/bolt-embedded-db-golang/) by Progville + + +## Comparison with other databases + +### Postgres, MySQL, & other relational databases + +Relational databases structure data into rows and are only accessible through +the use of SQL. This approach provides flexibility in how you store and query +your data but also incurs overhead in parsing and planning SQL statements. Bolt +accesses all data by a byte slice key. This makes Bolt fast to read and write +data by key but provides no built-in support for joining values together. + +Most relational databases (with the exception of SQLite) are standalone servers +that run separately from your application. This gives your systems +flexibility to connect multiple application servers to a single database +server but also adds overhead in serializing and transporting data over the +network. Bolt runs as a library included in your application so all data access +has to go through your application's process. This brings data closer to your +application but limits multi-process access to the data. + + +### LevelDB, RocksDB + +LevelDB and its derivatives (RocksDB, HyperLevelDB) are similar to Bolt in that +they are libraries bundled into the application, however, their underlying +structure is a log-structured merge-tree (LSM tree). An LSM tree optimizes +random writes by using a write ahead log and multi-tiered, sorted files called +SSTables. Bolt uses a B+tree internally and only a single file. Both approaches +have trade-offs. + +If you require a high random write throughput (>10,000 w/sec) or you need to use +spinning disks then LevelDB could be a good choice. If your application is +read-heavy or does a lot of range scans then Bolt could be a good choice. + +One other important consideration is that LevelDB does not have transactions. +It supports batch writing of key/values pairs and it supports read snapshots +but it will not give you the ability to do a compare-and-swap operation safely. +Bolt supports fully serializable ACID transactions. + + +### LMDB + +Bolt was originally a port of LMDB so it is architecturally similar. Both use +a B+tree, have ACID semantics with fully serializable transactions, and support +lock-free MVCC using a single writer and multiple readers. + +The two projects have somewhat diverged. LMDB heavily focuses on raw performance +while Bolt has focused on simplicity and ease of use. For example, LMDB allows +several unsafe actions such as direct writes for the sake of performance. Bolt +opts to disallow actions which can leave the database in a corrupted state. The +only exception to this in Bolt is `DB.NoSync`. + +There are also a few differences in API. LMDB requires a maximum mmap size when +opening an `mdb_env` whereas Bolt will handle incremental mmap resizing +automatically. LMDB overloads the getter and setter functions with multiple +flags whereas Bolt splits these specialized cases into their own functions. + + +## Caveats & Limitations + +It's important to pick the right tool for the job and Bolt is no exception. +Here are a few things to note when evaluating and using Bolt: + +* Bolt is good for read intensive workloads. Sequential write performance is + also fast but random writes can be slow. You can use `DB.Batch()` or add a + write-ahead log to help mitigate this issue. + +* Bolt uses a B+tree internally so there can be a lot of random page access. + SSDs provide a significant performance boost over spinning disks. + +* Try to avoid long running read transactions. Bolt uses copy-on-write so + old pages cannot be reclaimed while an old transaction is using them. + +* Byte slices returned from Bolt are only valid during a transaction. Once the + transaction has been committed or rolled back then the memory they point to + can be reused by a new page or can be unmapped from virtual memory and you'll + see an `unexpected fault address` panic when accessing it. + +* Be careful when using `Bucket.FillPercent`. Setting a high fill percent for + buckets that have random inserts will cause your database to have very poor + page utilization. + +* Use larger buckets in general. Smaller buckets causes poor page utilization + once they become larger than the page size (typically 4KB). + +* Bulk loading a lot of random writes into a new bucket can be slow as the + page will not split until the transaction is committed. Randomly inserting + more than 100,000 key/value pairs into a single new bucket in a single + transaction is not advised. + +* Bolt uses a memory-mapped file so the underlying operating system handles the + caching of the data. Typically, the OS will cache as much of the file as it + can in memory and will release memory as needed to other processes. This means + that Bolt can show very high memory usage when working with large databases. + However, this is expected and the OS will release memory as needed. Bolt can + handle databases much larger than the available physical RAM, provided its + memory-map fits in the process virtual address space. It may be problematic + on 32-bits systems. + +* The data structures in the Bolt database are memory mapped so the data file + will be endian specific. This means that you cannot copy a Bolt file from a + little endian machine to a big endian machine and have it work. For most + users this is not a concern since most modern CPUs are little endian. + +* Because of the way pages are laid out on disk, Bolt cannot truncate data files + and return free pages back to the disk. Instead, Bolt maintains a free list + of unused pages within its data file. These free pages can be reused by later + transactions. This works well for many use cases as databases generally tend + to grow. However, it's important to note that deleting large chunks of data + will not allow you to reclaim that space on disk. + + For more information on page allocation, [see this comment][page-allocation]. + +[page-allocation]: https://github.com/boltdb/bolt/issues/308#issuecomment-74811638 + + +## Reading the Source + +Bolt is a relatively small code base (<3KLOC) for an embedded, serializable, +transactional key/value database so it can be a good starting point for people +interested in how databases work. + +The best places to start are the main entry points into Bolt: + +- `Open()` - Initializes the reference to the database. It's responsible for + creating the database if it doesn't exist, obtaining an exclusive lock on the + file, reading the meta pages, & memory-mapping the file. + +- `DB.Begin()` - Starts a read-only or read-write transaction depending on the + value of the `writable` argument. This requires briefly obtaining the "meta" + lock to keep track of open transactions. Only one read-write transaction can + exist at a time so the "rwlock" is acquired during the life of a read-write + transaction. + +- `Bucket.Put()` - Writes a key/value pair into a bucket. After validating the + arguments, a cursor is used to traverse the B+tree to the page and position + where they key & value will be written. Once the position is found, the bucket + materializes the underlying page and the page's parent pages into memory as + "nodes". These nodes are where mutations occur during read-write transactions. + These changes get flushed to disk during commit. + +- `Bucket.Get()` - Retrieves a key/value pair from a bucket. This uses a cursor + to move to the page & position of a key/value pair. During a read-only + transaction, the key and value data is returned as a direct reference to the + underlying mmap file so there's no allocation overhead. For read-write + transactions, this data may reference the mmap file or one of the in-memory + node values. + +- `Cursor` - This object is simply for traversing the B+tree of on-disk pages + or in-memory nodes. It can seek to a specific key, move to the first or last + value, or it can move forward or backward. The cursor handles the movement up + and down the B+tree transparently to the end user. + +- `Tx.Commit()` - Converts the in-memory dirty nodes and the list of free pages + into pages to be written to disk. Writing to disk then occurs in two phases. + First, the dirty pages are written to disk and an `fsync()` occurs. Second, a + new meta page with an incremented transaction ID is written and another + `fsync()` occurs. This two phase write ensures that partially written data + pages are ignored in the event of a crash since the meta page pointing to them + is never written. Partially written meta pages are invalidated because they + are written with a checksum. + +If you have additional notes that could be helpful for others, please submit +them via pull request. + + +## Other Projects Using Bolt + +Below is a list of public, open source projects that use Bolt: + +* [BoltDbWeb](https://github.com/evnix/boltdbweb) - A web based GUI for BoltDB files. +* [Operation Go: A Routine Mission](http://gocode.io) - An online programming game for Golang using Bolt for user accounts and a leaderboard. +* [Bazil](https://bazil.org/) - A file system that lets your data reside where it is most convenient for it to reside. +* [DVID](https://github.com/janelia-flyem/dvid) - Added Bolt as optional storage engine and testing it against Basho-tuned leveldb. +* [Skybox Analytics](https://github.com/skybox/skybox) - A standalone funnel analysis tool for web analytics. +* [Scuttlebutt](https://github.com/benbjohnson/scuttlebutt) - Uses Bolt to store and process all Twitter mentions of GitHub projects. +* [Wiki](https://github.com/peterhellberg/wiki) - A tiny wiki using Goji, BoltDB and Blackfriday. +* [ChainStore](https://github.com/pressly/chainstore) - Simple key-value interface to a variety of storage engines organized as a chain of operations. +* [MetricBase](https://github.com/msiebuhr/MetricBase) - Single-binary version of Graphite. +* [Gitchain](https://github.com/gitchain/gitchain) - Decentralized, peer-to-peer Git repositories aka "Git meets Bitcoin". +* [event-shuttle](https://github.com/sclasen/event-shuttle) - A Unix system service to collect and reliably deliver messages to Kafka. +* [ipxed](https://github.com/kelseyhightower/ipxed) - Web interface and api for ipxed. +* [BoltStore](https://github.com/yosssi/boltstore) - Session store using Bolt. +* [photosite/session](https://godoc.org/bitbucket.org/kardianos/photosite/session) - Sessions for a photo viewing site. +* [LedisDB](https://github.com/siddontang/ledisdb) - A high performance NoSQL, using Bolt as optional storage. +* [ipLocator](https://github.com/AndreasBriese/ipLocator) - A fast ip-geo-location-server using bolt with bloom filters. +* [cayley](https://github.com/google/cayley) - Cayley is an open-source graph database using Bolt as optional backend. +* [bleve](http://www.blevesearch.com/) - A pure Go search engine similar to ElasticSearch that uses Bolt as the default storage backend. +* [tentacool](https://github.com/optiflows/tentacool) - REST api server to manage system stuff (IP, DNS, Gateway...) on a linux server. +* [Seaweed File System](https://github.com/chrislusf/seaweedfs) - Highly scalable distributed key~file system with O(1) disk read. +* [InfluxDB](https://influxdata.com) - Scalable datastore for metrics, events, and real-time analytics. +* [Freehold](http://tshannon.bitbucket.org/freehold/) - An open, secure, and lightweight platform for your files and data. +* [Prometheus Annotation Server](https://github.com/oliver006/prom_annotation_server) - Annotation server for PromDash & Prometheus service monitoring system. +* [Consul](https://github.com/hashicorp/consul) - Consul is service discovery and configuration made easy. Distributed, highly available, and datacenter-aware. +* [Kala](https://github.com/ajvb/kala) - Kala is a modern job scheduler optimized to run on a single node. It is persistent, JSON over HTTP API, ISO 8601 duration notation, and dependent jobs. +* [drive](https://github.com/odeke-em/drive) - drive is an unofficial Google Drive command line client for \*NIX operating systems. +* [stow](https://github.com/djherbis/stow) - a persistence manager for objects + backed by boltdb. +* [buckets](https://github.com/joyrexus/buckets) - a bolt wrapper streamlining + simple tx and key scans. +* [mbuckets](https://github.com/abhigupta912/mbuckets) - A Bolt wrapper that allows easy operations on multi level (nested) buckets. +* [Request Baskets](https://github.com/darklynx/request-baskets) - A web service to collect arbitrary HTTP requests and inspect them via REST API or simple web UI, similar to [RequestBin](http://requestb.in/) service +* [Go Report Card](https://goreportcard.com/) - Go code quality report cards as a (free and open source) service. +* [Boltdb Boilerplate](https://github.com/bobintornado/boltdb-boilerplate) - Boilerplate wrapper around bolt aiming to make simple calls one-liners. +* [lru](https://github.com/crowdriff/lru) - Easy to use Bolt-backed Least-Recently-Used (LRU) read-through cache with chainable remote stores. +* [Storm](https://github.com/asdine/storm) - Simple and powerful ORM for BoltDB. +* [GoWebApp](https://github.com/josephspurrier/gowebapp) - A basic MVC web application in Go using BoltDB. +* [SimpleBolt](https://github.com/xyproto/simplebolt) - A simple way to use BoltDB. Deals mainly with strings. +* [Algernon](https://github.com/xyproto/algernon) - A HTTP/2 web server with built-in support for Lua. Uses BoltDB as the default database backend. +* [MuLiFS](https://github.com/dankomiocevic/mulifs) - Music Library Filesystem creates a filesystem to organise your music files. +* [GoShort](https://github.com/pankajkhairnar/goShort) - GoShort is a URL shortener written in Golang and BoltDB for persistent key/value storage and for routing it's using high performent HTTPRouter. +* [torrent](https://github.com/anacrolix/torrent) - Full-featured BitTorrent client package and utilities in Go. BoltDB is a storage backend in development. +* [gopherpit](https://github.com/gopherpit/gopherpit) - A web service to manage Go remote import paths with custom domains + +If you are using Bolt in a project please send a pull request to add it to the list. |