Seems alright, but it is a bit of a bandaid. Is there no additional filter we could add to limit the size of the response?

Seems alright, but it is a bit of a bandaid. Is there no additional filter we could add to limit the size of the response?

For Github specifically, it is possible to use the Search issues and pull requests API to filter pull requests by the labels server-side which is very fast but this only returns the pull request numbers and would require N more API calls to get the necessary details (e.g. head sha) about each PR.

query := fmt.Sprintf("repo:%s/%s is:pr is:open", g.owner, g.repo)
for _, label := range g.labels {
	query += fmt.Sprintf(" label:\"%s\"", label)
}

opts := &github.SearchOptions{
	ListOptions: github.ListOptions{
		PerPage: 100,
	},
}
for {
	result, resp, err := g.client.Search.Issues(ctx, query, opts)
	...
}

For repos with large numbers of irrelevant PRs and a small number of relevant PRs this will be much faster but for smaller repos (which I assume are more common) then the existing code will be much faster. There seems to be no clear general solution.

Increasing page size is definitely a band aid but it might be the only reasonable thing that can be tuned with the REST API.

I will explore the GraphQL API instead.

I tested the GraphQL API in place of the REST API to list pull requests and it appears to be significantly faster with the following query using github.com/shurcooL/githubv4:

var query struct {
	Search struct {
		Nodes []struct {
			PullRequest struct {
				Number      githubv4.Int
				Title       githubv4.String
				HeadRefName githubv4.String
				BaseRefName githubv4.String
				HeadRefOid  githubv4.String
				Labels      struct {
					Nodes []githubLabel
				} `graphql:"labels(first: 10)"`
				Author struct {
					Login githubv4.String
				}
			} `graphql:"... on PullRequest"`
		}
		PageInfo struct {
			EndCursor   githubv4.String
			HasNextPage bool
		}
	} `graphql:"search(query: $query, type: ISSUE, first: 100, after: $after)"`
}

queryString := fmt.Sprintf("repo:%s/%s is:pr is:open", g.owner, g.repo)
for _, label := range g.labels {
	queryString += fmt.Sprintf(" label:\"%s\"", label)
}

I ran this against our largest repo which has over 4000 open PRs.

On my branch with GraphQL search query:

github_test.go:82: List function took 808.005791ms

On master:

    github_test.go:102: List function took 1m4.252771416s

I have a PR I can put up with this change and I am happy to test it internally at my company to validate it.