level-cache

An in memory cache on top of leveldb

Example

Exact same API as levelidb and levelup.

level-cache is one of two things. Either it's a complete in memory copy of the levelup API or it's a cache in front of leveldb.

var level = require("level-cache")

var db = level()
// in memory db

var level = require("level-cache")
    , levelup = require("levelidb")

var db = level(levelup(...))
// cache

level-cache uses lru-cache internally and you can pass in options to configure the internal cache through the API

var level = require("level-cache")

var db = level(db, {
    max: 20000
    , maxAge: 5 * 1000
})

Level cache has a synchronious get API if you don't pass a callback. It will return whatever is in the cache.

var level = require("level-cache")

var db = level(real_db, ...)

...

var value = db.get("key")

Level cache's asynchronous get will hit the cache by default and hit the real database if it doesn't have a value in the cache.

To get level cache to ignore it's local cache in a get just use the cache: false option

var level = require("level-cache")

var db = level(real_db, ...)

...

db.get("key", { cache: false }, function (err, value) {
    // from real db
})

Any callbacks passed to put, del or batch will be passed through to the real leveldb and will come back from the real db.

var level = require("level-cache")

var db = level(real_db, ...)

db.put(key, value)
// real_db.put is called and `db` will emit an `"error"` event
// if real_db returns an error.

db.put(key, value, function (err) {
    // result from real db
})

It should be noted that the readStream() implementation is currently naive. i.e. if a real db is passed to the cache it will just read from the real db and bypass the cache.

level cache only uses the cache with readStream() if you don't pass in a real database.

Kitchen sink example

var level = require("level-cache")
    , toArray = require("write-stream").toArray
    , assert = require("assert")

var db = level()

db.put("foo", { hello: "world" }, function (err) {
    if (err) {
        throw err
    }

    db.get("foo", function (err, value) {
        if (err) {
            throw err
        }

        assert.equal(value.hello, "world")

        console.log("value", value)
    })
})

var ten = makeTen()

db.batch(ten, function (err) {
    if (err) {
        throw err
    }

    var stream = db.readStream({
        start: "batch:"
        , end: "batch;"
    })

    stream.pipe(toArray(function (list) {
        console.log("list", list)

        list.forEach(function (item, index) {
            assert.equal(item.key, ten[index].key)
            assert.equal(item.value, ten[index].value)
        })
    }))

    var keyStream = db.keyStream({
        start: "batch:"
        , end: "batch;"
    })

    keyStream.pipe(toArray(function (list) {
        console.log("keys", list)

        list.forEach(function (item, index) {
            assert.equal(item, ten[index].key)
        })
    }))

    var valueStream = db.valueStream({
        start: "batch:"
        , end: "batch;"
    })

    valueStream.pipe(toArray(function (list) {
        list.forEach(function (item, index) {
            assert.equal(item, ten[index].value)
        })

        console.log("values", list)
    }))
})

var writable = db.writeStream()

writable.write({ key: "write:05", value: "5" })
writable.write({ key: "write:20", value: "20" })

writable.end()
writable.on("finish", function () {
    console.log("finished writing")

    var readable = db.valueStream({
        start: "write:"
        , end: "write;"
    })

    readable.pipe(toArray(function (list) {
        assert.equal(list[0], "5")
        assert.equal(list[1], "20")
        assert.equal(list.length, 2)

        console.log("values from writeStream", list)
    }))
})

function makeTen() {
    var list = []
    for (var i = 0; i < 10; i++) {
        list.push({
            type: "put"
            , key: "batch:" + i
            , value: i
        })
    }
    return list
}

Installation

npm install level-cache

Contributors

• Raynos

MIT Licenced