Cache repository default branch commit status to reduce query on commit status table (#29444)

After repository commit status has been introduced on dashaboard, the
most top SQL comes from `GetLatestCommitStatusForPairs`.

This PR adds a cache for the repository's default branch's latest
combined commit status. When a new commit status updated, the cache will
be marked as invalid.

<img width="998" alt="image"
src="https://github.com/go-gitea/gitea/assets/81045/76759de7-3a83-4d54-8571-278f5422aed3">

services/repository/commitstatus/commitstatus.go

@@ -0,0 +1,135 @@
+// Copyright 2024 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package commitstatus
+
+import (
+	"context"
+	"crypto/sha256"
+	"fmt"
+
+	"code.gitea.io/gitea/models/db"
+	git_model "code.gitea.io/gitea/models/git"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/cache"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/log"
+	api "code.gitea.io/gitea/modules/structs"
+	"code.gitea.io/gitea/services/automerge"
+)
+
+func getCacheKey(repoID int64, brancheName string) string {
+	hashBytes := sha256.Sum256([]byte(fmt.Sprintf("%d:%s", repoID, brancheName)))
+	return fmt.Sprintf("commit_status:%x", hashBytes)
+}
+
+func updateCommitStatusCache(ctx context.Context, repoID int64, branchName string, status api.CommitStatusState) error {
+	c := cache.GetCache()
+	return c.Put(getCacheKey(repoID, branchName), string(status), 3*24*60)
+}
+
+func deleteCommitStatusCache(ctx context.Context, repoID int64, branchName string) error {
+	c := cache.GetCache()
+	return c.Delete(getCacheKey(repoID, branchName))
+}
+
+// CreateCommitStatus creates a new CommitStatus given a bunch of parameters
+// NOTE: All text-values will be trimmed from whitespaces.
+// Requires: Repo, Creator, SHA
+func CreateCommitStatus(ctx context.Context, repo *repo_model.Repository, creator *user_model.User, sha string, status *git_model.CommitStatus) error {
+	repoPath := repo.RepoPath()
+
+	// confirm that commit is exist
+	gitRepo, closer, err := gitrepo.RepositoryFromContextOrOpen(ctx, repo)
+	if err != nil {
+		return fmt.Errorf("OpenRepository[%s]: %w", repoPath, err)
+	}
+	defer closer.Close()
+
+	objectFormat := git.ObjectFormatFromName(repo.ObjectFormatName)
+
+	commit, err := gitRepo.GetCommit(sha)
+	if err != nil {
+		return fmt.Errorf("GetCommit[%s]: %w", sha, err)
+	}
+	if len(sha) != objectFormat.FullLength() {
+		// use complete commit sha
+		sha = commit.ID.String()
+	}
+
+	if err := git_model.NewCommitStatus(ctx, git_model.NewCommitStatusOptions{
+		Repo:         repo,
+		Creator:      creator,
+		SHA:          commit.ID,
+		CommitStatus: status,
+	}); err != nil {
+		return fmt.Errorf("NewCommitStatus[repo_id: %d, user_id: %d, sha: %s]: %w", repo.ID, creator.ID, sha, err)
+	}
+
+	defaultBranchCommit, err := gitRepo.GetBranchCommit(repo.DefaultBranch)
+	if err != nil {
+		return fmt.Errorf("GetBranchCommit[%s]: %w", repo.DefaultBranch, err)
+	}
+
+	if commit.ID.String() == defaultBranchCommit.ID.String() { // since one commit status updated, the combined commit status should be invalid
+		if err := deleteCommitStatusCache(ctx, repo.ID, repo.DefaultBranch); err != nil {
+			log.Error("deleteCommitStatusCache[%d:%s] failed: %v", repo.ID, repo.DefaultBranch, err)
+		}
+	}
+
+	if status.State.IsSuccess() {
+		if err := automerge.MergeScheduledPullRequest(ctx, sha, repo); err != nil {
+			return fmt.Errorf("MergeScheduledPullRequest[repo_id: %d, user_id: %d, sha: %s]: %w", repo.ID, creator.ID, sha, err)
+		}
+	}
+
+	return nil
+}
+
+// FindReposLastestCommitStatuses loading repository default branch latest combinded commit status with cache
+func FindReposLastestCommitStatuses(ctx context.Context, repos []*repo_model.Repository) ([]*git_model.CommitStatus, error) {
+	results := make([]*git_model.CommitStatus, len(repos))
+	c := cache.GetCache()
+
+	for i, repo := range repos {
+		status, ok := c.Get(getCacheKey(repo.ID, repo.DefaultBranch)).(string)
+		if ok && status != "" {
+			results[i] = &git_model.CommitStatus{State: api.CommitStatusState(status)}
+		}
+	}
+
+	// collect the latest commit of each repo
+	// at most there are dozens of repos (limited by MaxResponseItems), so it's not a big problem at the moment
+	repoBranchNames := make(map[int64]string, len(repos))
+	for i, repo := range repos {
+		if results[i] == nil {
+			repoBranchNames[repo.ID] = repo.DefaultBranch
+		}
+	}
+
+	repoIDsToLatestCommitSHAs, err := git_model.FindBranchesByRepoAndBranchName(ctx, repoBranchNames)
+	if err != nil {
+		return nil, fmt.Errorf("FindBranchesByRepoAndBranchName: %v", err)
+	}
+
+	// call the database O(1) times to get the commit statuses for all repos
+	repoToItsLatestCommitStatuses, err := git_model.GetLatestCommitStatusForPairs(ctx, repoIDsToLatestCommitSHAs, db.ListOptionsAll)
+	if err != nil {
+		return nil, fmt.Errorf("GetLatestCommitStatusForPairs: %v", err)
+	}
+
+	for i, repo := range repos {
+		if results[i] == nil {
+			results[i] = git_model.CalcCommitStatus(repoToItsLatestCommitStatuses[repo.ID])
+			if results[i].State != "" {
+				if err := updateCommitStatusCache(ctx, repo.ID, repo.DefaultBranch, results[i].State); err != nil {
+					log.Error("updateCommitStatusCache[%d:%s] failed: %v", repo.ID, repo.DefaultBranch, err)
+				}
+			}
+		}
+	}
+
+	return results, nil
+}