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== Profile ==
[[File:Whf-white-2016-12.jpg|right|90px]]

Hengfeng Wei (魏恒峰)

* Research Assistant (助理研究员)：From 2017-01 

  Institute of Computer Software                          (软件所)
  State Key Laboratory for Novel Software Technology      (软件新技术国家重点实验室)
  Department of Computer Science and Technology           (计算机科学与技术系)
  Nanjing University （Xianlin Campus）                    (南京大学 仙林校区)
  Addr: 163 Xianlin Road, Qixia District, Nanjing, Jiangsu 210023, China     (江苏省南京市栖霞区仙林大道163号南京大学仙林校区 210023)

  Office: 302
  Mailbox: H016
  Email: [[File:Hfwei-njumail.png | hfwei-nju-edu-cn]]

== Research Interests ==

I am interested in Distributed Computing Theory and Formal Methods.

== Publications ==

[http://dblp.uni-trier.de/pers/hd/w/Wei:Hengfeng dblp: Hengfeng Wei] 

[https://scholar.google.com/citations?user=HK9-98EAAAAJ&hl=en scholar: Hengfeng Wei]

* [[#Specification Framework for Weakly Consistent Replicated Data Types | [SpecFramework]: Specification Framework for Weakly Consistent Replicated Data Types (WIP)]]
* [[#Jupiter Made Abstract, and then Refined | [RefineJupiter]: Jupiter Made Abstract, and then Refined (WIP)]]
* [[#Fine-grained Analysis on Fast Implementations of Multi-writer Atomic Registers of Multi-writer Atomic Registers | [FastAtomic@PODC2020]: Fine-grained Analysis on Fast Implementations of Multi-writer Atomic Registers of Multi-writer Atomic Registers]]
* [[#PaxosStore中共识算法TPaxos的推导、规约与精化 | [PaxosStore@软件学报2020] PaxosStore中共识算法TPaxos的推导、规约与精化]]
* [[#CRDT协议的TLA+ 描述与验证 | [CRDT@软件学报2020] CRDT协议的TLA+ 描述与验证]]
* [[#Specification and Implementation of Replicated List: The Jupiter Protocol Revisited | [Jupiter@OPODIS2018@PODC-BA2018]: Specification and Implementation of Replicated List: The Jupiter Protocol Revisited]]
* [[#Parameterized and Runtime-tunable Snapshot Isolation in Distributed Transactional Key-value Stores | [RVSI@SRDS2017]: Parameterized and Runtime-tunable Snapshot Isolation in Distributed Transactional Key-value Stores]]
* [[#Probabilistically-Atomic 2-Atomicity: Enabling Almost Strong Consistency in Distributed Storage Systems | [PA2AM@TC2017]: Probabilistically-Atomic 2-Atomicity: Enabling Almost Strong Consistency in Distributed Storage Systems]]
* [[#Verifying Pipelined-RAM Consistency over Read/Write Traces of Data Replicas | [VPC@TPDS2016]: Verifying Pipelined-RAM Consistency over Read/Write Traces of Data Replicas]]
* [[#Formal Specification and Runtime Detection of Temporal Properties for Asynchronous Context | [CTL3@PerCom2012]: Formal Specification and Runtime Detection of Temporal Properties for Asynchronous Context]]

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=== A Generic Specification Framework for Weakly Consistent Replicated Data Types ===
  .

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More details and comments are coming when the work is ready.
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=== Jupiter Made Abstract, and then Refined ===
  Under Review (JCST2020).

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More details and comments are coming when the work is ready.
</div>

=== Fine-grained Analysis on Fast Implementations of Multi-writer Atomic Registers of Multi-writer Atomic Registers ===

  Kaile Huang, Yu Huang, and '''Hengfeng Wei'''. 
  “Fine-grained Analysis on Fast Implementations of Multi-writer Atomic Registers of Multi-writer Atomic Registers”.
  In Proceedings of the ACM Symposium on Principles of Distributed Computing (PODC 2020), 2020.

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=== PaxosStore中共识算法TPaxos的推导、规约与精化 ===

  易星辰, '''魏恒峰''', 黄宇, 乔磊, 吕建. 
  PaxosStore中共识算法TPaxos的推导、规约与精化. 
  软件学报 2020. 2020年第8期 (已录用).

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=== CRDT协议的TLA+ 描述与验证 ===

  易星辰, '''魏恒峰''', 黄宇, 吕建. 
  CRDT协议的TLA+ 描述与验证.
  软件学报 2020. 2020年第6期.

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=== Specification and Implementation of Replicated List: The Jupiter Protocol Revisited ===
  
  '''Hengfeng Wei''', Yu Huang, and Jian Lu.
  “Specification and Implementation of Replicated List: The Jupiter Protocol Revisited”. 
  In: 22nd International Conference on Principles of Distributed Systems, OPODIS 2018, December 17-19, 2018, Hong Kong, China.
  2018, 12:1–12:16. url: https://doi.org/10.4230/LIPIcs.OPODIS.2018.12

  '''Hengfeng Wei''', Yu Huang, and Jian Lu.
  “Brief Announcement: Specification and Implementation of Replicated List: The Jupiter Protocol Revisited”.
  In: Proceedings of the 2018 ACM Symposium on Principles of Distributed Computing. PODC ’18.
  Egham, United Kingdom: ACM, 2018, pp. 81–83. url: http://doi.acm.org/10.1145/3212734.3212

 [[Media:jupiter-podc18-ba.pdf | Paper: Jupiter@PODC-BA'2018]] [[Media:Jupiter-opodis18.pdf | Paper: Jupiter@OPODIS'2018]] [[Media:1708.04754.pdf | [Paper: Jupiter@arXiv (full version)]]]

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This work is inspired by the work on [http://software.imdea.org/~gotsman/papers/editing-podc16.pdf "Specification and Complexity of Collaborative Text Editing"] published in PODC'2016 by Hagit Attiya et al.

More details and comments are coming when the work is ready.
</div>

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=== Parameterized and Runtime-tunable Snapshot Isolation in Distributed Transactional Key-value Stores ===

  '''Hengfeng Wei''', Yu Huang, Jian Lu.
  Parameterized and Runtime-tunable Snapshot Isolation in Distributed Transactional Key-value Stores.
  In ''Proc. of the 36th International Symposium on Reliable Distributed Systems (SRDS)'', pp. 21--33, Hong Kong, China, Sep.2017.
  [[Media:SRDS17_Parameterized_and_Runtime-tunable_Snapshot_Isolation_in_Distributed_Transactional_Key-value_Stores.pdf|[Paper:RVSI@SRDS17]]]

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The formal specification of RVSI (Relaxed Version Snapshot Isolation) in this work is partly inspired by the work on [https://ai2-s2-pdfs.s3.amazonaws.com/0590/4e9741b2d3d9090807408ac9fb5da344c21e.pdf "Relaxed Currency Serializability for Middle-Tier Caching and Replication"] published in SIGMOD'2006 by Philip A.Bernstein ''et al''. 

It is the first time we use Aliyun in our experiments. This will be the normal case in the future.

'''''Important Lessons Learnt:''''' 
* Solve the real problems in realistic ways!
  One can always find made up examples of ..., but it is hard to convince that .... 
  This paper does not go beyond ....                          --- From Reviewers
* System research greatly matters!
  The following is all about the experimental section, which is probably the weakest part of the paper.
                                                              --- From Reviewers

</div>
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=== Probabilistically-Atomic 2-Atomicity: Enabling Almost Strong Consistency in Distributed Storage Systems ===

  '''Hengfeng Wei''', Yu Huang, Jian Lu. 
  Probabilistically-Atomic 2-Atomicity: Enabling Almost Strong Consistency in Distributed Storage Systems. 
  In ''IEEE Trans. Comput.'' (IEEE Transactions on Computers), 66(3):502--514, doi:10.1109/TC.2016.2601322, March 2017.
  [http://ieeexplore.ieee.org/document/7547362/ [abstract@IEEE]] [[Media:Probabilistically-Atomic 2-Atomicity Enabling Almost Strong Consistency in Distributed Storage Systems.pdf | [Paper: PA2AM@TC'2017]]] [https://arxiv.org/abs/1507.01663 [Paper: PA2AM@arXiv (not up-to-date)]]

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Last night (2016-10-13), I reread the paper [http://research.microsoft.com/en-us/um/people/lamport/pubs/pubs.html#interprocess "On Interprocess Communication --- Part II: Algorithms"] of Leslie Lamport, and found that in Proposition 5, Lamport has proved that in the single-writer model a regular register is atomic if two successive reads that overlap the same write cannot obtain the new then the old value. The phenomenon that "two successive reads that overlap the same write cannot obtain the new then the old value" is exactly the old-new inversion anomaly. Therefore, Lamport has shown that a regular register is atomic if it does not allow old-new inversion anomalies. This is very similar to Theorem 1 in our paper which essentially states that the PA2AM algorithm implements a 2-atomic register ''and'' the old-new inversion anomaly is the only cause of atomicity violation.

The major difference between Proposition 5 of Lamport and Theorem 1 in our paper is that Proposition 5 is at the specification level while Theorem 1 is at the implementation level.

Combining Proposition 5 and Theorem 1, we obtain 

; Conjecture 1 
: In the single-writer model, 2-atomicity is equivalent to regularity.

; Conjecture 2
: In the single-write model, PA2AM implements a regular register.
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=== Verifying Pipelined-RAM Consistency over Read/Write Traces of Data Replicas ===

  '''Hengfeng Wei''', Marzio De Biasi, Yu Huang, Jiannong Cao, and Jian Lu. 
  Verifying Pipelined-RAM Consistency over Read/Write Traces of Data Replicas.
  In ''IEEE Trans. Parallel Distrib. Syst.'', 27(5):1511--1523, May 2016, doi:10.1109/TPDS.2015.2453985
  [http://ieeexplore.ieee.org/document/7152941/ [abstract@IEEE]] [[Media:Verifying Pipelined-RAM Consistency over Read Write Traces of Data Replicas.pdf | [Paper: VPC@TPDS'2016]]] [https://arxiv.org/abs/1302.5161 [Paper: VPC@arXiv(not up-to-date)]]
  SCI: DJ5HS

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In the Conclusion section, we discussed the VCC (Verifying [http://link.springer.com/article/10.1007/BF01784241 Causal Consistency]) problem and wrote: "Because Pipelined-RAM is a weakening of causal consistency, our NP-complete result also applies to the general problem of verifying causal consistency". 

I am sorry to say that it is not right for us to conclude that VCC, in general, (i.e., VCC-SD in our terms) is NP-complete just because Pipelined-RAM is a weakening of causal consistency.

However, I think that VCC-SD is NP-complete and that the basic idea of the polynomial reduction used in the NP-complete proof for VPC-SD will be useful in proving the NP-completeness of VCC-SD.

The NP-completeness proof for VPC-SD (along with VPC-MD) is mainly credited to [http://www.nearly42.org/ Marzio De Biasi], the second author of this paper.
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=== Formal Specification and Runtime Detection of Temporal Properties for Asynchronous Context ===

  '''Hengfeng Wei''', Yu Huang, Jiannong Cao, Xiaoxing Ma, Jian Lu. 
  Formal Specification and Runtime Detection of Temporal Properties for Asynchronous Context. 
  In ''Proceedings of the 10th IEEE International Conference on Pervasive Computing and Communications 
  (IEEE PerCom '12)'', pages 30--38, 2012.
  [http://ieeexplore.ieee.org/document/6199846/ [abstract@IEEE]] [[Media:Formal Specification and Runtime Detection of Temporal Properties for Asynchronous Context.pdf | [Paper: CTL3@PerCom'2012]]]
  EI: 20122315082503

== Projects ==

== Links ==

* [https://github.com/hengxin hengxin@GitHub]

* [http://stackexchange.com/users/2055160 hengxin@StackExchange]