barcode plugin excel 2007 Data Access in Software

Printing ANSI/AIM Code 128 in Software Data Access

1723 Data Access
Code 128A Generation In None
Using Barcode drawer for Software Control to generate, create USS Code 128 image in Software applications.
Code 128 Code Set C Decoder In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
As we saw in 11, the database system resides permanently on nonvolatile storage (usually disks), and is partitioned into xed-length storage units called blocks Blocks are the units of data transfer to and from disk, and may contain several data
Generating USS Code 128 In C#.NET
Using Barcode maker for .NET Control to generate, create USS Code 128 image in .NET applications.
Code 128B Generator In .NET
Using Barcode generation for ASP.NET Control to generate, create ANSI/AIM Code 128 image in ASP.NET applications.
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
Painting Code 128 In VS .NET
Using Barcode generation for .NET Control to generate, create Code 128 Code Set B image in .NET framework applications.
Code 128B Maker In VB.NET
Using Barcode drawer for VS .NET Control to generate, create Code 128A image in Visual Studio .NET applications.
V Transaction Management
Draw Data Matrix In None
Using Barcode printer for Software Control to generate, create DataMatrix image in Software applications.
Bar Code Generation In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
17 Recovery System
Code 128C Maker In None
Using Barcode creation for Software Control to generate, create Code 128C image in Software applications.
EAN-13 Encoder In None
Using Barcode drawer for Software Control to generate, create EAN 13 image in Software applications.
The McGraw Hill Companies, 2001
Code 3/9 Encoder In None
Using Barcode printer for Software Control to generate, create Code 39 image in Software applications.
Barcode Printer In None
Using Barcode generation for Software Control to generate, create bar code image in Software applications.
Storage Structure
UCC - 14 Generation In None
Using Barcode generation for Software Control to generate, create UPC Case Code image in Software applications.
Encoding Code-39 In None
Using Barcode generator for Online Control to generate, create Code 3/9 image in Online applications.
input(A) A output(B) B B
GS1 DataBar Truncated Drawer In Java
Using Barcode maker for Java Control to generate, create GS1 RSS image in Java applications.
Barcode Encoder In Java
Using Barcode maker for Java Control to generate, create barcode image in Java applications.
disk main memory
Paint Barcode In Objective-C
Using Barcode encoder for iPad Control to generate, create bar code image in iPad applications.
Bar Code Decoder In Java
Using Barcode scanner for Java Control to read, scan read, scan image in Java applications.
Figure 171 Block storage operations
Encoding Data Matrix 2d Barcode In .NET
Using Barcode maker for Reporting Service Control to generate, create ECC200 image in Reporting Service applications.
Print USS Code 128 In Java
Using Barcode generator for BIRT Control to generate, create Code 128A image in BIRT reports applications.
items We shall assume that no data item spans two or more blocks This assumption is realistic for most data-processing applications, such as our banking example Transactions input information from the disk to main memory, and then output the information back onto the disk The input and output operations are done in block units The blocks residing on the disk are referred to as physical blocks; the blocks residing temporarily in main memory are referred to as buffer blocks The area of memory where blocks reside temporarily is called the disk buffer Block movements between disk and main memory are initiated through the following two operations: 1 input(B) transfers the physical block B to main memory 2 output(B) transfers the buffer block B to the disk, and replaces the appropriate physical block there Figure 171 illustrates this scheme Each transaction Ti has a private work area in which copies of all the data items accessed and updated by Ti are kept The system creates this work area when the transaction is initiated; the system removes it when the transaction either commits or aborts Each data item X kept in the work area of transaction Ti is denoted by xi Transaction Ti interacts with the database system by transferring data to and from its work area to the system buffer We transfer data by these two operations: 1 read(X) assigns the value of data item X to the local variable xi It executes this operation as follows: a If block BX on which X resides is not in main memory, it issues input(BX ) b It assigns to xi the value of X from the buffer block 2 write(X) assigns the value of local variable xi to data item X in the buffer block It executes this operation as follows: a If block BX on which X resides is not in main memory, it issues input(BX ) b It assigns the value of xi to X in buffer BX
Silberschatz Korth Sudarshan: Database System Concepts, Fourth Edition
V Transaction Management
17 Recovery System
The McGraw Hill Companies, 2001
17
Recovery System
Note that both operations may require the transfer of a block from disk to main memory They do not, however, speci cally require the transfer of a block from main memory to disk A buffer block is eventually written out to the disk either because the buffer manager needs the memory space for other purposes or because the database system wishes to re ect the change to B on the disk We shall say that the database system performs a force-output of buffer B if it issues an output(B) When a transaction needs to access a data item X for the rst time, it must execute read(X) The system then performs all updates to X on xi After the transaction accesses X for the nal time, it must execute write(X) to re ect the change to X in the database itself The output(BX ) operation for the buffer block BX on which X resides does not need to take effect immediately after write(X) is executed, since the block BX may contain other data items that are still being accessed Thus, the actual output may take place later Notice that, if the system crashes after the write(X) operation was executed but before output(BX ) was executed, the new value of X is never written to disk and, thus, is lost
173 Recovery and Atomicity
Consider again our simpli ed banking system and transaction Ti that transfers $50 from account A to account B, with initial values of A and B being $1000 and $2000, respectively Suppose that a system crash has occurred during the execution of Ti , after output(BA ) has taken place, but before output(BB ) was executed, where BA and BB denote the buffer blocks on which A and B reside Since the memory contents were lost, we do not know the fate of the transaction; thus, we could invoke one of two possible recovery procedures: Reexecute Ti This procedure will result in the value of A becoming $900, rather than $950 Thus, the system enters an inconsistent state Do not reexecute Ti The current system state has values of $950 and $2000 for A and B, respectively Thus, the system enters an inconsistent state In either case, the database is left in an inconsistent state, and thus this simple recovery scheme does not work The reason for this dif culty is that we have modi ed the database without having assurance that the transaction will indeed commit Our goal is to perform either all or no database modi cations made by Ti However, if Ti performed multiple database modi cations, several output operations may be required, and a failure may occur after some of these modi cations have been made, but before all of them are made To achieve our goal of atomicity, we must rst output information describing the modi cations to stable storage, without modifying the database itself As we shall see, this procedure will allow us to output all the modi cations made by a committed transaction, despite failures There are two ways to perform such outputs; we study them in Sections 174 and 175 In these two sections, we shall assume that
Copyright © OnBarcode.com . All rights reserved.