Implementing The Fieldalignment Bundle in Go

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This simple optimization improves the performance of a Go program with minimal effort. It also has never been implemented until now. The fieldalignment bundle is a technique that you can use to minimize the amount of memory your application uses during runtime. This can result in a performance improvement due to the semantics of the Go Garbage Collector.

What is Struct Padding?

A system’s architecture (32-bit, 64-bit) defines the size (in bits) of each word and how the memory of the system is aligned. The first factor serves as the basis for the size of primitive types (i.e string, int, uint, etc) in the Go programming language. As an example, the sizes of basic types can be found in go/types/sizes.go:131.

The second factor serves as the basis for struct padding, which aligns the fields of structs to addresses in memory. This is done by padding — adding extra — bytes to a struct so it’s size is a multiple of a valid word size (i.e 8 bytes * multiple on 64-bit systems). The purpose of struct padding is to improve the performance of memory usage and prevent numerous other issues on a system’s architecture.

For more information on memory alignment, read Memory Layouts (Go) and Dealing With Maligned Structs.

What is Fieldalignment?

Fieldalignment is the process of aligning the fields in Go structs in order to minimize the size of the struct (in memory). As an example, reorganizing the order of a struct’s fields can reduce its size from 24 bytes to 16 bytes. In the Go programming language, issues with fieldalignment can be fixed using the fieldalignment tool which is installed using go install golang.org/x/tools/go/analysis/passes/fieldalignment/cmd/fieldalignment@latest.

Using the fieldalignment command will tell you where misaligned fields are in your program. Using the -fix flag will fix these issues for you while using -json will print out diagnostics in the JSON format. As a WARNING, running fieldalignment -fix ./... may remove comments from your fields due to the underlying difficulty in manipulating free-floating comments within the Go Abstract Syntax Tree. This problem is being resolved in https://github.com/golang/go/issues/20744, but it has taken Go's creators 5…