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In
distributed data base and transaction systems a distributed commit
protocol is required to ensure that the effects of a distributed
transaction are atomic, that is, either all the effects of the transaction
persist or none persist, whether or not failures occur. Several commit
protocols have been proposed in the literature. These are variations of
what has become a standard and known as the two-phase commit (2PC)
protocol.
Related
Publications:
Apart
from other specific publications certain contributions on commit protocols
are presented in invited chapters:
 |
Chrysanthis,
P., Samaras, G., and Y. Al-Houmail "Recovery
and Performance of Atomic Commit Protocols in Distributed and
Multidatabase Systems",
(Invited chapter in) V. Kumar and M. Hsu (Eds), Performance of Database Recovery Mechanism, forthcoming 1997 |
| Samaras
G., K. Britton,
A. Citron,
C. Mohan, "Two-Phase
Commit Optimizations and Trade offs in the Commercial Environment",
selected to be included in Advances
in Concurrency Control and Transaction Processing by K. Ramamritham and P.K.
Chrysanthis, IEEE Computer
Science Press, ISBN 0-1886-7405-9, 1996 |
|
Samaras,
G., and P. Chrysanthis "Commit
Protocols", A chapter
in: The Encyclopedia of Distributed Computing, P. Dasgupta and J.
Urban, Editors, Kluwer Academic Publishers,
forthcoming 2000. |
|
Samaras
G., K. Britton,
A. Citron,
C. Mohan, "Enhancing
SNA's LU6.2 Sync Point
to Include Presumed Abort Protocol", TR# 29.1751.
Embedded as chapter 5 in IBM's book publication "Systems Network Architecture, Sync Point Services Architecture",
SC31-8134-00, Sept. 1994. |
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Samaras
G., K. Britton,
A. Citron, "Systems
Network Architecture, Sync Point Services Architecture", IBM
Book, SC31-8134-00,
September 1994. Presents IBM's distributed transaction processing
architecture. Published and distributed by IBM. This architecture is
being implemented by IBM's VM, DB2, CICS, AS400, Transarc's Encina,
Tandem and Bull. |
Much
of the literature focuses on improving performance in failure cases by
providing a non-blocking 2PC that streamlines recovery processing at the
expense of extra processing in the normal case.
We focused on improving performance in the normal case based on two
assumptions: first, that networks and systems are becoming increasingly
reliable, and second, that the need to support high-volume transactions
requires a streamlined protocol for the normal case. Our work resulted in
a number of optimizations most of which have been incorporated
in IBM and non-IBM transactional offerings. These optimizations were
presented and analyzed in terms of reliability, savings in log writes and
network traffic, and reduction in resource lock time.
Our work's unique contributions include the description of some
optimizations not described elsewhere in the literature and a systematic
comparison of the optimizations and the environments where they cause the
most benefit. Furthermore, it analyzed the feasibility and performance of
several combinations of the optimizations and identifies situations where
optimizations can be combined effectively. Optimizing for the non-failure
case has been, also, demonstrated through this work as the correct
approach towards commit optimization. These results have been published in
the refered following publications and have significantly influence
further work in commit protocols.
Related
Publications:
|
Samaras
G., K. Britton,
A. Citron, "Systems
Network Architecture, Sync Point Services Architecture", SC31-8134-00,
September 1994. Presents IBM's distributed transaction processing
architecture. Published and distributed by IBM. This architecture is
being implemented by IBM's VM, DB2, CICS, AS400, Transarc's Encina,
Tandem and Bull |
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Samaras
G., K. Britton,
A. Citron,
C. Mohan , "Two-Phase
Commit Optimizations in a Commercial
Distributed Environment", Distributed
and Parallel Databases Journal,
3(4): 325-361, October, 1995 |
|
Samaras
G., K. Britton, A. Citron, C. Mohan, "Two-Phase
Commit Optimizations and Trade offs in the Commercial Environment",
Proc. 9th
International Data Engineering Conference, IEEE, Vienna,
April 1993. |
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Samaras,
G., Kyrou G., P. Chrysanthis, "Structuring
the Commit Tree to Improve Commit Processing". Proc.
9th Hellenic Conference on Informatics, Nicosia, Cyprus, November
2001.
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Optimizing
for the non-failure case does not mean that the ramifications on commit
processing due to failure is not of any interest. The reliability aspect
of commit processing is extremely important and we could not considered
our work fundamentally complete without studying the impact of commit
failures in various environments. Heuristic decisions (HD) and their
effect on 2PC reliability have been little addressed in the literature but
they are considered a practical necessity in the commercial environment.
This part of my work argued the importance of incorporating
heuristics decisions in commit protocols and studied the effect of doing
so. It provided a comprehensive study of
heuristics decisions: how and when they occur, how they are
process, and the importance of being identified and effectively reported
to the transaction or commit initiator.
It studied how commit protocols are affected and proposed a 2PC
protocol variant, called Presumed Nothing (PrN), that effectively handles
heuristic decisions. It described how certain commit optimizations can be
used to tune the variant's performance around application requirements,
and presented an appropriate commit programming interface. Finally, we
studied the effect of adding HD to the main commit variations, such as PA,
PC and IBM-PN showing that all collapse (almost) to the PrN.
Related
Publications:
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Samaras,
G., S.D. Nikolopoulos, "Algorithmic Techniques Incorporating Heuristic
Decisions in Commit Protocols". Proc.
25th Euromicro Conference, IEEE/CS, Como, September
1995. |
| Samaras,
G. and S. D. Nikolopoulos, "Heuristic
Decisions and Commit Protocols", TR# 96-17, University of
Cyprus, Computer Science Department. |
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Mohan,
C., K. Britton,
A. Citron, G. Samaras , "Generalized
Presumed Abort: Marrying Presumed Abort and SNA's LU6.2 Commit
Protocols', An Iternational
Workashop on Advance Transaction Models and Architectures (ATMA96) (Edited
Book), Goa, India, September 1996 (Held in conjuction with VLDB'96).
Extended version of the HPTS'93 paper. |
While
commit protocol variants (i.e., PA, PC, IBM-PN, PrN, EP, CL, etc.) provide
certain efficiencies, when forced in cooperation for the commitment of a
distributed transaction in heterogeneous systems, problems and
incompatibilities arise.
These incompatibilities appear because of the differences in the
commit protocol variants each one of the participants uses. Even if the
different participants support the same commit variant, problems might
again exist if these variants support
different
commit optimizations. Work in the first three following
publications represents the first ever effort in integrating commit protocols. Specifically, the
first two, describe the integration of
PA and IBM-PN since these are the dominant commit protocols in use.
The resulted protocol, called
generalized presumed abort (GPA), has already being implemented in IBM's
DB2 V.4, AS400 and CICS.
In
our recent work we studied how the different commit protocol variants,
enhanced with optimizations
or not, can coexist in the form of a universal commit protocol that
allows the execution of distributed transactions in heterogeneous systems.
This universal commit protocols is called "All Two-phase Commit"
(ALL2PC). This work resulted in a BS thesis (the last publication
below) at the University of Cyprus and is in preparation for conference
and journal publication.
Related
Publications:
|
Samaras
G., K. Britton,
A. Citron,
C. Mohan , "Enhancing
SNA's LU6.2 Sync Point
to Include Presumed Abort Protocol", IBM
Technical Report, TR# 29.1751, IBM Research Triangle Park, August
1993.. Embedded as chapter 5 in IBM's book publication "Systems
Network Architecture, Sync Point Services Architecture",
SC31-8134-00, Sept., 1994. |
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Mohan,
C., K. Britton,
A. Citron, G. Samaras , "Generalized
Presumed Abort: Marrying Presumed Abort and SNA's LU6.2 Commit
Protocols',
Proc. 4th International
Workshop on High Performance Transaction Systems (HPTS), Asilomar,
September 1993 |
|
Mohan,
C., K. Britton,
A. Citron, G. Samaras , "Generalized
Presumed Abort: Marrying Presumed Abort and SNA's LU6.2 Commit
Protocols', An Iternational
Workashop on Advance Transaction Models and Architectures (ATMA96) (Edited
Book), Goa, India, September 1996 (Held in conjuction with VLDB'96).
Extended version of the HPTS'93 paper. |
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Andreou
Andreas, "Integration of Commit protocols", BS thesis,
Supervisor: George Samaras . Dept. of
Computer Science University of Cyprus, May, 1996 |
Commit
protocols over the years have been extensively optimized to improve
performance and system throughput in terms of reliability, savings in log
writes and network traffic, and reduction in resource lock time. Every proposed optimization, however, aimed to improve the
protocols performance without ever taking into consideration application
semantics and needs. This resulted in protocols that could satisfy with
good performance only part of applications needs while other requirements
could not even be supported. Work in the second publication below provides
the ability to adapt commit processing around application semantics. It
presents an application requirements classification and commit
optimizations that can be used to tune the different variant's performance
around application needs, and describes an appropriate commit programming
interface. A performance evaluation demonstrates the superior performance
that can be achieved if application needs are considered in the
choice of commit processing. The motivation and need for this work came
about from the work on "Integration
of Commit Protocol Variants" and "Heuristic Decisions and Commit
Protocols".
The final goal of this work is to tie together adaptability and
integration under one scope.
Related
Publications:
|
Samaras
G., K. Britton,
A. Citron,
C. Mohan , "Two-Phase
Commit Optimizations in a Commercial
Distributed Environment", Distributed
and Parallel Databases Journal,
3(4): 325-361, October, 1995. |
|
Samaras,
G., On the Semantic
Adaptability of Commit Protocols",
technical report TR-98-6, University of Cyprus, April 1998.
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