Segmentio/encoding: optimized drop-in replacement for Go's encoding/JSON...

encoding

Go package containing implementations of encoders and decoders for various data formats.

Motivation

At Segment, we do a lot of marshaling and unmarshaling of data when sending, queuing, or storing messages. The resources we need to provision on the infrastructure are directly related to the type and amount of data that we are processing. At the scale we operate at, the tools we choose to build programs can have a large impact on the efficiency of our systems. It is important to explore alternative approaches when we reach the limits of the code we use.

This repository includes experiments for Go packages for marshaling and unmarshaling data in various formats. While the focus is on providing a high performance library, we also aim for very low development and maintenance overhead by implementing APIs that can be used as drop-in replacements for the default solutions.

encoding/json

The json sub-package provides a re-implementation of the functionalities offered by the standard library's encoding/json package, with a focus on lowering the CPU and memory footprint of the code.

The exported API of this package mirrors the standard library's encoding/json package, the only change needed to take advantage of the performance improvements is the import path of the json package, from:

import (
    "encoding/json"
)

to

import (
    "github.com/segmentio/encoding/json"
)

The improvement can be significant for code that heavily relies on serializing and deserializing JSON payloads. The CI pipeline runs benchmarks to compare the performance of the package with the standard library and other popular alternatives; here's an overview of the results (using Go v1.13):

Comparing to encoding/json

benchmark                                  old ns/op     new ns/op     delta
BenchmarkMarshal/*json.codeResponse2       7589434       6581487       -13.28%
BenchmarkUnmarshal/*json.codeResponse2     33979780      9130120       -73.13%

benchmark                                  old MB/s     new MB/s     speedup
BenchmarkMarshal/*json.codeResponse2       255.68       294.84       1.15x
BenchmarkUnmarshal/*json.codeResponse2     57.11        212.54       3.72x

benchmark                                  old allocs     new allocs     delta
BenchmarkMarshal/*json.codeResponse2       0              0              +0.00%
BenchmarkUnmarshal/*json.codeResponse2     76400          39             -99.95%

benchmark                                  old bytes     new bytes     delta
BenchmarkMarshal/*json.codeResponse2       0             0             +0.00%
BenchmarkUnmarshal/*json.codeResponse2     1901670       8483          -99.55%

Comparing to github.com/json-iterator/go

benchmark                                  old ns/op     new ns/op     delta
BenchmarkMarshal/*json.codeResponse2       15065785      6581487       -56.32%
BenchmarkUnmarshal/*json.codeResponse2     10275368      9130120       -11.15%

benchmark                                  old MB/s     new MB/s     speedup
BenchmarkMarshal/*json.codeResponse2       128.80       294.84       2.29x
BenchmarkUnmarshal/*json.codeResponse2     188.85       212.54       1.13x

benchmark                                  old allocs     new allocs     delta
BenchmarkMarshal/*json.codeResponse2       102212         0              -100.00%
BenchmarkUnmarshal/*json.codeResponse2     37120          39             -99.89%

benchmark                                  old bytes     new bytes     delta
BenchmarkMarshal/*json.codeResponse2       3399409       0             -100.00%
BenchmarkUnmarshal/*json.codeResponse2     1038339       8483          -99.18%

Although this package aims to be a drop-in replacement of encoding/json , it does not guarantee the same error messages. It will error in the same cases as the standard library, but the exact error message may be different.

encoding/iso8601

The iso8601 sub-package exposes APIs to efficiently deal with with string representations of iso8601 dates.

Data formats like JSON have no syntaxes to represent dates, they are usually serialized and represented as a string value. In our experience, we often have to check whether a string value looks like a date, and either construct a time.Time by parsing it or simply treat it as a string . This check can be done by attempting to parse the value, and if it fails fallback to using the raw string. Unfortunately, while the happy path for time.Parse is fairly efficient, constructing errors is much slower and has a much bigger memory footprint.

We've developed fast iso8601 validation functions that cause no heap allocations to remediate this problem. We added a validation step to determine whether the value is a date representation or a simple string. This reduced CPU and memory usage by 5% in some programs that were doing time.Parse calls on very hot code paths.