Boltdb Raw Save

A simple library for working with raw Go struct data.

Project README

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This is simple library for working with raw Go struct data. Most of the time it's good to serialize your data to a common encoding format (e.g. JSON, MessagePack, Protocol Buffers) when saving and retrieving data to disk or sending over a network. These encodings can provide a common interface for data and support versioning and other useful features.

However, serialization comes at a cost. Converting between types and copying memory all has overhead so when you need to go really fast, sometimes you need to skip serialization all together.



Go provides the ability to perform type conversion on byte slices to convert them into pointers of Go types. You can do this using the unsafe package. As the name suggests, it's not safe. You need to know what you're doing.

// Create a byte slice with 4 bytes.
b := make([]byte, 4)

// Create an 32-bit int pointer to the first byte of the slice and set a value.
x := (*int32)(unsafe.Pointer(&b[0]))
*x = 1000

// Verify that the underlying byte slice changed.
fmt.Printf("%x\n", b)

This will print out the value: e8030000 which is the hex representation of 1000.

Using Raw

The primitive integer and float types in Go map directly to byte slices. However, the string type does not. Its internal representation is publicly accessible or guaranteed not to change between Go versions. So to map variable length Go strings to byte slices in our code we can use the raw.String type:

var s String
b := make([]byte, unsafe.Sizeof(s))
s.Encode("foo", &b)
copy(b, (*[unsafe.Sizeof(s)]byte)(unsafe.Pointer(&s))[:])

That will encode the string offset and length followed by the bytes, "foo". Then when you want to use the string, type convert the byte slice to your raw.String and extract the data:

s := ((*raw.String)(unsafe.Pointer(&b[0])))

// Prints: foo

If this seems like a lot of work just to encode a string then you'd be correct. However, it's fast and when multiple strings are combined in a struct it allows us to only deserialize the fields we need.


To get an idea of the performance of this approach, please see the benchmarks inside the test suite.

On my Intel Core i7 2.9GHz Macbook Pro, I see the following stats:

$ go test -bench=. -benchmem
BenchmarkString_Encode	10000000	       214 ns/op	      64 B/op	       3 allocs/op
BenchmarkString_Decode	500000000	         3.77 ns/op	       0 B/op	       0 allocs/op
ok	4.635s


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