---
title: Performance
---

## Memory Usage

A trade-off between memory usage and execution time can be controlled by [`GOGC`](https://golang.org/pkg/runtime/#hdr-Environment_Variables) environment variable.
Less `GOGC` values trigger garbage collection more frequently and golangci-lint consumes less memory and more CPU. Below is the trade-off table for running on this repo:

| `GOGC`          | Peak Memory, GB | Execution Time, s |
| --------------- | --------------- | ----------------- |
| `5`             | 1.1             | 60                |
| `10`            | 1.1             | 34                |
| `20`            | 1.3             | 25                |
| `30`            | 1.6             | 20.2              |
| `50`            | 2.0             | 17.1              |
| `80`            | 2.2             | 14.1              |
| `100` (default) | 2.2             | 13.8              |
| `off`           | 3.2             | 9.3               |

## Why `golangci-lint` is so fast

1. Work sharing

   During operation, `golangci-lint` shares work between specific linters (like `golint`, `govet`, etc.).
   We don't fork to call a specific linter, but instead use its API.
   For small and medium projects 50-90% of work between linters can be reused.

   - load `[]*packages.Package` by `go/packages` once

     We load program (parsing all files and type-checking) only once for all linters. For the most of linters
     it's the most heavy operation: it takes 5 seconds on 8 kLoC repo and 11 seconds on `$GOROOT/src`.

   - build `ssa.Program` once

     Some linters (megacheck, interfacer, unparam) work on SSA representation.
     Building of this representation takes 1.5 seconds on 8 kLoC repo and 6 seconds on `$GOROOT/src`.

   - parse source code and build AST once

     Parsing one source file takes 200 us on average. Parsing of all files in `$GOROOT/src` takes 2 seconds.
     Currently we parse each file more than once because it's not the bottleneck. But we already save a lot of
     extra parsing. We're planning to parse each file only once.

   - walk files and directories once

     It takes 300-1000 ms for `$GOROOT/src`.

2. Smart linters scheduling

   We schedule linters by a special algorithm which takes estimated execution time into account. It allows
   to save 10-30% of time when one of heavy linters (megacheck etc) is enabled.

3. Don't fork to run shell commands

All linters has their version fixed with go modules, they are builtin
and you don't need to install them separately.
