Newcomers are critical for the success and continuity of open source software (OSS) projects. To attract newcomers and facilitate their onboarding, many OSS projects recommend tasks for newcomers, such as good first issues (GFIs). Previous studies have preliminarily investigated the effects of GFIs and techniques to identify suitable GFIs. However, it is still unclear whether just recommending tasks is enough and how significant mentoring is for newcomers. To better understand mentoring in OSS communities, we analyze the resolution process of 48,402 GFIs from 964 repositories through a mix-method approach. We investigate the extent, the mentorship structures, the discussed topics, and the relevance of expert involvement. We find that $\sim$70\% of GFIs have expert participation, with each GFI usually having one expert who makes two comments. Half of GFIs will receive their first expert comment within 8.5 hours after a newcomer comment. Through analysis of the collaboration networks of newcomers and experts, we observe that community mentorship presents four types of structure: centralized mentoring, decentralized mentoring, collaborative mentoring, and distributed mentoring. As for discussed topics, we identify 14 newcomer challenges and 18 expert mentoring content. By fitting the generalized linear models, we find that expert involvement positively correlates with newcomers' successful contributions but negatively correlates with newcomers' retention. Our study manifests the status and significance of mentoring in the OSS projects, which provides rich practical implications for optimizing the mentoring process and helping newcomers contribute smoothly and successfully.

翻译：新手对于开源软件（OSS）项目的成功与持续性至关重要。为吸引新手并促进其融入，许多OSS项目会向其推荐任务，例如"好上手问题"（GFIs）。已有研究初步探讨了GFIs的效果及识别合适GFIs的技术。然而，仅推荐任务是否足够，以及指导对新手的重要性仍不明确。为更好地理解OSS社区中的指导机制，我们采用混合方法分析了来自964个仓库的48,402个GFIs的解决过程，探究专家参与程度、指导结构、讨论主题以及与专家参与的关联性。研究发现，约70%的GFIs有专家参与，每个GFI通常有一名专家做出两条评论。半数GFIs在收到新手评论后的8.5小时内会获得首条专家评论。通过分析新手与专家的协作网络，我们观察到社区指导呈现四种结构类型：集中式指导、分散式指导、协作式指导和分布式指导。在讨论主题方面，我们识别出14个新手挑战与18项专家指导内容。通过拟合广义线性模型，我们发现专家参与与新人成功贡献正相关，但与其留存率负相关。本研究揭示了OSS项目中指导的现状与重要性，为优化指导流程、助力新手顺利且成功做出贡献提供了丰富的实践启示。