scispace - formally typeset

Journal ArticleDOI

A real-time locking protocol

01 Jul 1991-IEEE Transactions on Computers (IEEE Computer Society)-Vol. 40, Iss: 7, pp 793-800

TL;DR: It is shown that this protocol leads to freedom from mutual deadlock and can be used by schedulability analysis to guarantee that a set of periodic transactions using this protocol can always meet its deadlines.

AbstractThe authors examine a priority driven two-phase lock protocol called the read/write priority ceiling protocol. It is shown that this protocol leads to freedom from mutual deadlock. In addition, a high-priority transactions can be blocked by lower priority transactions for at most the duration of a single embedded transaction. These properties can be used by schedulability analysis to guarantee that a set of periodic transactions using this protocol can always meet its deadlines. Finally, the performance of this protocol is examined for randomly arriving transactions using simulation studies. >

Summary (2 min read)

1. Introduction

  • In a real-time database context, concurrency control protocols must not only maintain the consistency constraints of the database but also satisfy the timing requirements of the transactions accessing the database.
  • Next, the authors process transactions in priority order.
  • The preemption of T3, and hence the blocking of T1, will continue until T2 and any other pending intermediate-priority level transactions are completed.
  • An objective of this paper is to design an appropriate priority management protocol for a given concurrency control protocol so that deadlocks can be avoided and the duration of blocking can be tightly bounded.

2.1. Basic Concepts

  • Real-time databases are often used by applications such as tracking.
  • The authors assume that an embedded transaction consists of a sequence of read and write operations operating upon the database.
  • Task τ0 will therefore continue and execute its transaction, thereby effectively preempting T2 in its transaction and not encountering any blocking.

2.2. Definitions and Properties

  • Having reviewed the basic concepts, the authors now review their assumptions and state the notation used.
  • The authors also assume that a transaction does not attempt to lock an object that it has already locked and thus deadlock with itself.
  • Under the read- or write-priority ceiling protocol, mutual deadlock of transactions cannot occur and each task can be blocked by at most one embedded transaction until it completes or suspends itself.
  • The authors now develop a set of sufficient conditions under which a set of periodic tasks with hard deadlines at the end of the periods can be scheduled by the rate-monotonic algorithm [15] when the read- or write-priority ceiling protocol is used.

3. Performance Evaluation

  • In the previous section, the authors have assumed that all the tasks are periodic and that all the database objects are in the main memory.
  • For each experiment and for each algorithm tested, the authors collected performance statistics and averaged over 10 runs.
  • The two important factors affecting the performance of locking protocols are their abilities to resolve the locking conflicts and to perform the I/O and transactions in parallel.
  • The main weakness of the read- or write-priority ceiling protocol is its inability to perform I/O and transactions in parallel.
  • In their experiments, each transaction’s deadline is set proportional to its size and system workload (number of transactions), and the transaction with the shorter deadline is assigned a higher priority.

4. Conclusions

  • Real-time database is an important area of research, with applications ranging from surveillance to reliable manufacturing and production control.
  • The authors have investigated the read- or write-priority ceiling protocol, which integrates the two-phase lock protocol with priority-driven real-time scheduling.
  • The authors have also developed schedulability bounds for periodic tasks in a centralized in-core database.
  • Finally, the authors experimentally evaluated the performance of this protocol when the tasks are invoked aperiodically and the database is no longer in-core.

Did you find this useful? Give us your feedback

...read more

Content maybe subject to copyright    Report

Technical Report
CMU/SEI-89-TR-018
ESD-89-TR-026
A Real-Time Locking Protocol
Lui Sha
Ragunathan Rajkumar
Sang Son
Chun-Hyon Chang
April 1989

A Real-Time Locking Protocol
AB
Software Engineering Institute
Carnegie Mellon University
Pittsburgh, Pennsylvania 15213
Technical Report
CMU/SEI-89-TR-018
ESD-89-TR-026
April 1989
Lui Sha
Real-Time Scheduling in Ada Project
Ragunathan Rajkumar
Carnegie Mellon University
Sang Son
University of Virginia
Chun-Hyon Chang
Kon Kuk University, Seoul, Korea
Unlimited distribution subject to the copyright.

This report was prepared for the SEI Joint Program Office HQ ESC/AXS
5 Eglin Street
Hanscom AFB, MA 01731-2116
The ideas and findings in this report should not be construed as an official DoD position. It is
published in the interest of scientific and technical information exchange.
FOR THE COMMANDER
(signature on file)
Thomas R. Miller, Lt Col, USAF, SEI Joint Program Office
This work is sponsored by the U.S. Department of Defense.
Copyright 1989 by Carnegie Mellon University.
Permission to reproduce this document and to prepare derivative works from this document for internal use is granted, provided the copyright and
\‘No Warranty\’ statements are included with all reproductions and derivative works. Requests for permission to reproduce this document or to
prepare derivative works of this document for external and commercial use should be addressed to the SEI Licensing Agent.
NO WARRANTY
THIS CARNEGIE MELLON UNIVERSITY AND SOFTWARE ENGINEERING INSTITUTE MATERIAL IS FURNISHED ON AN \‘AS-IS\’ BASIS.
CARNEGIE MELLON UNIVERSITY MAKES NO WARRANTIES OF ANY KIND, EITHER EXPRESSED OR IMPLIED, AS TO ANY MATTER
INCLUDING, BUT NOT LIMITED TO, WARRANTY OF FITNESS FOR PURPOSE OR MERCHANTIBILITY, EXCLUSIVITY, OR RESULTS
OBTAINED FROM USE OF THE MATERIAL. CARNEGIE MELLON UNIVERSITY DOES NOT MAKE ANY WARRANTY OF ANY KIND WITH
RESPECT TO FREEDOM FROM PATENT, TRADEMARK, OR COPYRIGHT INFRINGEMENT.
This work was created in the performance of Federal Government Contract Number F19628-95-C-0003 with Carnegie Mellon University for the
operation of the Software Engineering Institute, a federally funded research and development center. The Government of the United States has a
royalty-free government-purpose license to use, duplicate, or disclose the work, in whole or in part and in any manner, and to have or permit
others to do so, for government purposes pursuant to the copyright license under the clause at 52.227-7013.
This document is available through Asset Source for Software Engineering Technology (ASSET) / 1350 Earl L. Core Road ; P.O. Box 3305 /
Morgantown, West Virginia 26505 / Phone: (304) 284-9000 / Fax: (304) 284-9001 / e-mail: sei@asset.com / WWW:
http://www.asset.com/sei.html
Copies of this document are available through the National Technical Information Service (NTIS). For information on ordering, please contact
NTIS directly: National Technical Information Service / U.S. Department of Commerce / Springfield, VA 22161. Phone: (703) 487-4600.
This document is also available through the Defense Technical Information Center (DTIC). DTIC provides acess to and transfer of scientific and
technical information for DoD personnel, DoD contractors and potential con tractors, and other U.S. Government agency personnel and their
contractors. To obtain a copy, please contact DTIC directly: Defense Technical Information Center / 8725 John J. Kingman Road / Suite 0944 /
Ft. Belvoir, VA 22060-6218. Phone: 1-800-225-3842 or 703-767-8222.

1
Use of any trademarks in this report is not intended in any way to infringe on the rights of the trademark holder.

CMU/SEI-89-TR-18 1
A Real-Time
Locking Protocol
Abstract: When a database system is used in a real-time application, the concur-
rency control protocol must satisfy not only the consistency of shared data but
also the timing constraints of the application. In this paper, we examine a priority-
driven two-phase lock protocol called the read- or write-priority ceiling protocol.
We show that this protocol is free of deadlock, and in addition a high-priority trans-
action can be blocked by lower priority transactions for at most the duration of a
single embedded transaction. We then evaluate system performance experimen-
tally.
1. Introduction
In a real-time database context, concurrency control protocols must not only maintain the
consistency constraints of the database but also satisfy the timing requirements of the trans-
actions accessing the database.
Both concurrency control [2, 3, 4, 5, 7, 16, 17, 18, 20, 21, 23, 26] and real-time scheduling
algorithms [10, 11, 13, 14, 15, 19, 22, 27] are active areas of research in their own right. It
may seem that the development of a real-time locking protocol is a simple matter of combin-
ing priority scheduling with a locking protocol. For example, we may require each trans-
action to use a well-known concurrency protocol such as the two-phase lock protocol [6] and
assign priorities to transactions according to some well-known scheduling algorithms such
as the earliest deadline algorithm [19]. Next, we process transactions in priority order. Un-
fortunately, such an approach may lead to unbounded priority inversion, in which a high-
priority task would wait for lower priority tasks for an indefinite period of time.
Example 1: Suppose T
1
, T
2
, and T
3
are three transactions arranged in descending order of
priority, with T
1
having the highest priority. Assume that transaction T
1
and T
3
share the
same data object O. Suppose that at time
t
1
transaction T
3
obtains a write-lock on O.
During the execution of T
3
, the high-priority task T
1
arrives and attempts to read-lock the
object O. Transaction T
1
will be blocked, since O is already write-locked. We would expect
that T
1
, being the highest priority transaction, will be blocked no longer than the time for T
3
to complete and unlock O. However, the duration of blocking may, in fact, be unbounded.
This is because transaction T
3
can be preempted by the intermediate-priority transaction T
2
that does not need to access O. The preemption of T
3
, and hence the blocking of T
1
, will
continue until T
2
and any other pending intermediate-priority level transactions are com-
pleted.
The blocking duration in Example 1 can be arbitrarily long. This situation can be partially
remedied if transactions are not allowed to be preempted; however, this solution is only ap-
propriate for very short transactions, because it creates unnecessary blocking. For instance,

Citations
More filters

Journal ArticleDOI
TL;DR: This 25th year anniversary paper for the IEEE Real Time Systems Symposium reviews the key results in real-time scheduling theory and the historical events that led to the establishment of the current real- time computing infrastructure.
Abstract: In this 25th year anniversary paper for the IEEE Real Time Systems Symposium, we review the key results in real-time scheduling theory and the historical events that led to the establishment of the current real-time computing infrastructure. We conclude this paper by looking at the challenges ahead of us.

622 citations


Cites background or methods from "A real-time locking protocol"

  • ...Sha, Rajkumar and Lehoczky introduced the family of priority inheritance protocols as a solution approach to the priority inversion problem [192, 196, 197, 178]....

    [...]

  • ...It is the basis of several locking protocols, including the Priority Ceiling Protocol (PCP), [192, 196, 197, 178, 176], the Stack Resource Protocol (SRP) [27], the Ada 95 programming language ceiling locking protocol [29], and the POSIX mutex PTHREAD PRIO PROTECT protocol[64]....

    [...]


Journal ArticleDOI
Abstract: A temporal database contains time-varying data. In a real-time database transactions have deadlines or timing constraints. In this paper we review the substantial research in these two previously separate areas. First we characterize the time domain; then we investigate temporal and real-time data models. We evaluate temporal and real-time query languages along several dimensions. We examine temporal and real-time DBMS implementation. Finally, we summarize major research accomplishments to date and list several unanswered research questions. >

512 citations


Journal ArticleDOI
01 Jan 1994
TL;DR: This paper develops a taxonomy of the underlying design space of concurrency control including the various techniques for achieving serializability and improving performance and discusses several approaches that explore the nonserializable semantics of real-time transactions to meet the hard deadlines.
Abstract: In addition to maintaining database consistency as in conventional databases, real-time database systems must also handle transactions with timing constraints. While transaction response time and throughput are usually used to measure a conventional database system, the percentage of transactions satisfying the deadlines or a time-critical value function is often used to evaluate a real-time database system. Scheduling real-time transactions is far more complex than traditional real-time scheduling in the sense that (1) worst case execution times are typically hard to estimate, since not only CPU but also I/O requirement is involved; and (2) certain aspects of concurrency control may not integrate well with real-time scheduling. In this paper, we first develop a taxonomy of the underlying design space of concurrency control including the various techniques for achieving serializability and improving performance. This taxonomy provides us with a foundation for addressing the real-time issues. We then consider the integration of concurrency control with real-time requirements. The implications of using run policies to better utilize real-time scheduling in a database environment are examined. Finally, as timing constraints may be more important than data consistency in certain hard realtime database applications, we also discuss several approaches that explore the nonserializable semantics of real-time transactions to meet the hard deadlines. >

181 citations


Cites background or methods from "A real-time locking protocol"

  • ...In [58], a xed priority was used for the priority ceiling approach....

    [...]

  • ...The priority ceiling scheme in [57, 58] can reduce the blocking time to one transaction execution 16...

    [...]

  • ...In [57, 58], a read/write priority ceiling protocol was proposed where a high priority transaction can be blocked by at most the duration of a single low priority transaction....

    [...]


Proceedings ArticleDOI
05 Dec 1990
TL;DR: A new concurrency control algorithm for real-time database systems is proposed, by which real- time scheduling and concurrency Control can be integrated.
Abstract: A new concurrency control algorithm for real-time database systems is proposed, by which real-time scheduling and concurrency control can be integrated. The algorithm is founded on a priority-based locking mechanism to support time-critical scheduling by adjusting the serialization order dynamically in favor of high priority transactions. Furthermore, it does not assume any knowledge about the data requirements or execution time of each transaction, making the algorithm very practical. >

144 citations


Book ChapterDOI
21 Mar 1995
TL;DR: This paper presents an integrated system, which provides database operations with real-time constraints is generally called a real- time database system (RTDBS) and explains its development and use case.
Abstract: Traditionally, real-time systems manage their data (e.g. chamber temperature, aircraft locations) in application dependent structures. As real-time systems evolve, their applications become more complex and require access to more data. It thus becomes necessary to manage the data in a systematic and organized fashion. Database management systems provide tools for such organization, so in recent years there has been interest in “merging” database and real-time technology. The resulting integrated system, which provides database operations with real-time constraints is generally called a real-time database system (RTDBS) [1].

131 citations


References
More filters

Book
03 Jan 1989
Abstract: The problem of multiprogram scheduling on a single processor is studied from the viewpoint of the characteristics peculiar to the program functions that need guaranteed service. It is shown that an optimum fixed priority scheduler possesses an upper bound to processor utilization which may be as low as 70 percent for large task sets. It is also shown that full processor utilization can be achieved by dynamically assigning priorities on the basis of their current deadlines. A combination of these two scheduling techniques is also discussed.

5,242 citations


Book
01 Feb 1987
Abstract: This book is an introduction to the design and implementation of concurrency control and recovery mechanisms for transaction management in centralized and distributed database systems. Concurrency control and recovery have become increasingly important as businesses rely more and more heavily on their on-line data processing activities. For high performance, the system must maximize concurrency by multiprogramming transactions. But this can lead to interference between queries and updates, which concurrency control mechanisms must avoid. In addition, a satisfactory recovery system is necessary to ensure that inevitable transaction and database system failures do not corrupt the database.

3,890 citations


Journal ArticleDOI
TL;DR: An investigation is conducted of two protocols belonging to the priority inheritance protocols class; the two are called the basic priority inheritance protocol and the priority ceiling protocol, both of which solve the uncontrolled priority inversion problem.
Abstract: An investigation is conducted of two protocols belonging to the priority inheritance protocols class; the two are called the basic priority inheritance protocol and the priority ceiling protocol. Both protocols solve the uncontrolled priority inversion problem. The priority ceiling protocol solves this uncontrolled priority inversion problem particularly well; it reduces the worst-case task-blocking time to at most the duration of execution of a single critical section of a lower-priority task. This protocol also prevents the formation of deadlocks. Sufficient conditions under which a set of periodic tasks using this protocol may be scheduled is derived. >

2,399 citations


"A real-time locking protocol" refers background in this paper

  • ...With only two-phase locking and priority assignment, we can encounter the problem of unbounded priority inversion as illustrated in Example 1. However, the idea of priority inheritance [ 24 ] solves the unbounded priority inversion problem....

    [...]


Journal ArticleDOI
TL;DR: It is argued that a transaction needs to lock a logical rather than a physical subset of the database, and an implementation of predicate locks which satisfies the consistency condition is suggested.
Abstract: In database systems, users access shared data under the assumption that the data satisfies certain consistency constraints. This paper defines the concepts of transaction, consistency and schedule and shows that consistency requires that a transaction cannot request new locks after releasing a lock. Then it is argued that a transaction needs to lock a logical rather than a physical subset of the database. These subsets may be specified by predicates. An implementation of predicate locks which satisfies the consistency condition is suggested.

2,005 citations


"A real-time locking protocol" refers methods in this paper

  • ...Each embedded transaction will follow the two-phase lock protocol [ 6 ], which requires a transaction to acquire all the locks before it releases any lock....

    [...]

  • ...For example, we may require each transaction to use a well-known concurrency protocol such as the two-phase lock protocol [ 6 ] and assign priorities to transactions according to some well-known scheduling algorithms such as the earliest deadline algorithm [19]....

    [...]


Proceedings ArticleDOI
05 Dec 1989
TL;DR: An exact characterization of the ability of the rate monotonic scheduling algorithm to meet the deadlines of a periodic task set and a stochastic analysis which gives the probability distribution of the breakdown utilization of randomly generated task sets are represented.
Abstract: An exact characterization of the ability of the rate monotonic scheduling algorithm to meet the deadlines of a periodic task set is represented. In addition, a stochastic analysis which gives the probability distribution of the breakdown utilization of randomly generated task sets is presented. It is shown that as the task set size increases, the task computation times become of little importance, and the breakdown utilization converges to a constant determined by the task periods. For uniformly distributed tasks, a breakdown utilization of 88% is a reasonable characterization. A case is shown in which the average-case breakdown utilization reaches the worst-case lower bound of C.L. Liu and J.W. Layland (1973). >

1,551 citations


"A real-time locking protocol" refers background in this paper

  • ...An exact characterization of rate-monotonic schedulability can be found in [ 12 ]....

    [...]


Frequently Asked Questions (1)
Q1. What are the contributions mentioned in the paper "A real-time locking protocol" ?

In this paper, the authors examine a prioritydriven two-phase lock protocol called the reador write-priority ceiling protocol. The authors show that this protocol is free of deadlock, and in addition a high-priority transaction can be blocked by lower priority transactions for at most the duration of a single embedded transaction. The authors then evaluate system performance experimentally.