Boltdb-key-Value Data Store purely in Go

Question

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.

As this is the case,is there any connection pooling concept like various clients connecting and accessing the database at the same time.? Is this possible in boltdb?Like there are various connections reading and writing in the database at the same time.How it can be implemented?

Answer 1

A Bolt database is usually embedded into a larger program and is not used over the network like you would with shared databases (think SQLite vs MySQL). Using Bolt is a bit like having a persistent map[[]byte][]byte if that were possible. Depending on what you are doing, you might want to just use something like Redis.

That said, if you need to use Bolt this way, it is not very difficult to wrap with a simple server. Here is an example that writes/reads keys from a Bolt DB over HTTP. You can use Keep-Alive for connection pooling.

Code at: https://github.com/skyec/boltdb-server

package main

import (
    "flag"
    "fmt"
    "io/ioutil"
    "log"
    "net/http"
    "time"

    "github.com/boltdb/bolt"
    "github.com/gorilla/mux"
)

type server struct {
    db *bolt.DB
}

func newServer(filename string) (s *server, err error) {
    s = &server{}
    s.db, err = bolt.Open(filename, 0600, &bolt.Options{Timeout: 1 * time.Second})
    return
}

func (s *server) Put(bucket, key, contentType string, val []byte) error {
    return s.db.Update(func(tx *bolt.Tx) error {
        b, err := tx.CreateBucketIfNotExists([]byte(bucket))
        if err != nil {
            return err
        }
        if err = b.Put([]byte(key), val); err != nil {
            return err
        }
        return b.Put([]byte(fmt.Sprintf("%s-ContentType", key)), []byte(contentType))
    })
}

func (s *server) Get(bucket, key string) (ct string, data []byte, err error) {
    s.db.View(func(tx *bolt.Tx) error {
        b := tx.Bucket([]byte(bucket))
        r := b.Get([]byte(key))
        if r != nil {
            data = make([]byte, len(r))
            copy(data, r)
        }

        r = b.Get([]byte(fmt.Sprintf("%s-ContentType", key)))
        ct = string(r)
        return nil
    })
    return
}

func (s *server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    vars := mux.Vars(r)

    if vars["bucket"] == "" || vars["key"] == "" {
        http.Error(w, "Missing bucket or key", http.StatusBadRequest)
        return
    }

    switch r.Method {
    case "POST", "PUT":
        data, err := ioutil.ReadAll(r.Body)
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }
        err = s.Put(vars["bucket"], vars["key"], r.Header.Get("Content-Type"), data)
        w.WriteHeader(http.StatusOK)
    case "GET":
        ct, data, err := s.Get(vars["bucket"], vars["key"])
        if err != nil {
            http.Error(w, err.Error(), http.StatusInternalServerError)
            return
        }
        w.Header().Add("Content-Type", ct)
        w.Write(data)
    }
}

func main() {
    var (
        addr   string
        dbfile string
    )

    flag.StringVar(&addr, "l", ":9988", "Address to listen on")
    flag.StringVar(&dbfile, "db", "/var/data/bolt.db", "Bolt DB file")
    flag.Parse()

    log.Println("Using Bolt DB file:", dbfile)
    log.Println("Listening on:", addr)

    server, err := newServer(dbfile)
    if err != nil {
        log.Fatalf("Error: %s", err)
    }

    router := mux.NewRouter()
    router.Handle("/v1/buckets/{bucket}/keys/{key}", server)
    http.Handle("/", router)

    log.Fatal(http.ListenAndServe(addr, nil))
}

Answer 2

There is no connection pooling concept in boltdb, because there is no connection. It is not a client/server database, it is an embedded database (like sqlite or Berkeley-DB).

Boltdb is designed so that multiple goroutines of the same process can access the database at the same time (using different transactions). The model is single writer, multiple readers. Boltdb is not designed to support accesses from multiple processes.

If you need a Go program to use an embedded database supporting access from multiple processes at the same time, you may want to have a look at the wrappers over LMDB, such as:

• https://github.com/szferi/gomdb
• https://github.com/armon/gomdb