GoPark

GoPark is a naive local version porting of Spark/Dpark, MapReduce(R) alike computing framework supporting iterative computation.

GoPark is implemented in Go languange, and provides the cocurrent MapReduce(R) data operations using GoRoutines. It can only run in the local mode, but you can specify the concurrent numbers.

Examples

Examples for computing PI:

package main

import (
    "fmt"
    "github.com/mijia/gopark"
    "math/rand"
)

func main() {
    gopark.ParseOptions()
    c := gopark.NewContext("ComputePI")
    defer c.Stop()

    N := 100000
    iters := c.Data(make([]interface{}, N))
    count := iters.Map(func(_ interface{}) interface{} {
        x := rand.Float32()
        y := rand.Float32()
        if x*x+y*y < 1 {
            return 1
        } else {
            return 0
        }
    }).Reduce(func(x, y interface{}) interface{} {
        return x.(int) + y.(int)
    }).(int)
    fmt.Println("Pi =", (4.0 * float64(count) / float64(N)))
}

The above code can be runned as (using 4 go routines concurrently.)

$ go run hello.go -p=4

Checkout the examples/ for more cases.

interface{}

As the examples shows, since Go only provides the interface{} as the root type for everything and the type check/assertion is very strict in golang, so all the apis are implemented using the interface{} as the parameters. Have to do the type asserting in the closure functions. This also applies to the []interface{}.

The basic closure functions are like,

type MapperFunc func(interface{}) interface{}
type PartitionMapperFunc func([]interface{}) []interface{}
type FlatMapperFunc func(interface{}) []interface{}
type ReducerFunc func(interface{}, interface{}) interface{}
type FilterFunc func(interface{}) bool
type LoopFunc func(interface{})

Shuffle and Shuffle_N like funcs

Some functions which do shuffle job like GroupByKey() also provides the GroupByKey_N() func, which user can specify the numPartitions that job should run on. Please check rdd.go for references.

Encode / Gob

For the shuffle jobs like GroupByKey() and Persist(), GoPark uses encoding/gob as the encoder/decoder into local files, since GoPark uses interface{} as the parameters, GOB need to know what the interface{} actually is when decoding. Which can be done like the kmeans.go example shows,

type CenterCounter struct {
    X     gopark.Vector
    Count int
}

gob.Register(new(CenterCounter))

and you cannot use structs with unexported fields. Just be careful with this, if you got runtime panics, please check

• if you have use a complicated struct
• if you hadn't register the type on GOB, even like type T int
• if you have use slices of slices of slices .... Just make sure GOB knows your objects behind the interface{} and []interface{}.

Things not included

So far, the Broadcast are still not implemented. I am just using the vars in closure.

And GoPark now really cannot run in the distributed mode.

Have fun~

Originally, I have only two goals in writing this,

• Write some real stuff in Go, since I am learning the language
• I am doing data mining jobs and I need some better concurrent framework for performance, and runs locally is ok for me.

Spark/DPark

These projects are really awesome and the RDD is really a fantastic data structure or design pattern. I learned a lot in them.

Really want to thank these two projects.