Posted: Wed May 10, 2006 4:14 am Post subject: about vsam update
hi all,
I did a transaction in cics,after that I use STARTOOL to view the vsam,no data update,but after I close vsam in cics and open it again,I can see it.what parameter affect this?I mean why it was not updated immediately?
SHAREOPTIONS(crossregion[ crosssystem]]1 3)
specifies how an alternate index's data or index component can be shared among users.
For data integrity purposes, you should make sure that share options specified for data and index components are the same. For a description of data set sharing, see DFSMS/MVS Using Data Sets.
crossregion
specifies the amount of sharing allowed among regions within the same system or within multiple systems using global resource serialization (GRS). Independent job steps in an operating system or multiple systems using GRS can access a VSAM data set concurrently. To share a data set, each user must specify DISP=SHR in the data set's DD statement. The values that can be specified are:
1
specifies that the data set can be shared by any number of users for read processing, or the data set can be accessed by only one user for read and write processing. With this option, VSAM ensures complete data integrity for the data set.
2
specifies that the data set can be accessed by any number of users for read processing and it can also be accessed by one user for write processing. With this option, VSAM ensures write integrity by obtaining exclusive control for a control interval when it is to be updated. If a user requires read integrity, it is that user's responsibility to use the ENQ and DEQ macros appropriately to provide read integrity for the data the program obtains. (For information on using ENQ and DEQ, see OS/390 MVS Programming: Authorized Assembler Services Reference ALE-DYN and OS/390 MVS Programming: Authorized Assembler Services Reference ENF-IXG.)
3
specifies that the data set can be fully shared by any number of users. With this option, each user is responsible for maintaining both read and write integrity for the data the program accesses. User programs that ignore the write integrity guidelines can cause VSAM program checks, lost or inaccessible records, irreversible data set failures, and other unpredictable results. This option places heavy responsibility on each user sharing the data set.
4
specifies that the data set can be fully shared by any number of users, and buffers used for direct processing are refreshed for each request. This option requires your program to use the ENQ and DEQ macros to maintain data integrity while sharing the data set. Improper use of the ENQ macro can cause problems similar to those described under SHAREOPTIONS 3. (For information on using ENQ and DEQ, see OS/390 MVS Programming: Authorized Assembler Services Reference ALE-DYN and OS/390 MVS Programming: Authorized Assembler Services Reference ENF-IXG.)
crosssystem
specifies the amount of sharing allowed among systems. Job steps of two or more operating systems can gain access to the same VSAM data set regardless of the disposition specified in each step's DD statement for the data set.
To get exclusive control of the data set's volume, a task in one system issues the RESERVE macro. The level of cross-system sharing allowed by VSAM applies only in a multiple operating system environment. The values that can be specified are:
1
Reserved
2
Reserved
3
specifies that the data set can be fully shared. With this option, each user is responsible for maintaining both read and write integrity for the data that user's program accesses. User programs that ignore write integrity guidelines can cause VSAM program checks, irreversible data set failures, and other unpredictable results. This option places heavy responsibility on each user sharing the data set.
4
specifies that the data set can be fully shared. Buffers used for direct processing are refreshed for each request. This option requires that you use the RESERVE and DEQ macros to maintain data integrity while sharing the data set. Improper use of the RESERVE macro can cause problems similar to those described under SHAREOPTIONS 3. For information on using RESERVE and DEQ, see OS/390 MVS Programming: Authorized Assembler Services Reference ALE-DYN and OS/390 MVS Programming: Authorized Assembler Services Reference LLA-SDU. Writing is limited to PUT-update and PUT-insert processing that does not change the high-used RBA if your program opens the data set with DISP=SHR. Data set integrity cannot be maintained unless all jobs accessing the data set in a cross-system environment specify DISP=SHR.
To ensure data integrity in a shared environment, VSAM provides users of SHAREOPTIONS 4 (cross-region and cross-system) with the following assistance:
Each PUT request results in the appropriate buffer being written immediately into the VSAM object's direct access device space. VSAM writes out the buffer in the user's address space that contains the new or updated data record.
Each GET request results in all the user's input buffers being refreshed. The contents of each data and index buffer being used by the user's program are retrieved from the VSAM object's direct access device.
sorry,I can't get it.
Those transaction had done successful for sure,at beginning I thought it was a time-delay.But after I finished 6 transactions,then closed and opened this vsam,those new inserted records appear in the vsam without any other operation.
Joined: 26 Nov 2002 Posts: 12376 Topics: 75 Location: San Jose
Posted: Wed May 10, 2006 7:31 am Post subject:
Quote:
sorry,I can't get it.
Read carefully the following sentences under share option 4
Quote:
To ensure data integrity in a shared environment, VSAM provides users of SHAREOPTIONS 4 (cross-region and cross-system) with the following assistance:
Each PUT request results in the appropriate buffer being written immediately into the VSAM object's direct access device space. VSAM writes out the buffer in the user's address space that contains the new or updated data record.
Each GET request results in all the user's input buffers being refreshed. The contents of each data and index buffer being used by the user's program are retrieved from the VSAM object's direct access device.
Remember that with share options (4 4) your performance will degrade
Writing is limited to PUT-update and PUT-insert processing that does not change the high-used RBA if your program opens the data set with DISP=SHR. Data set integrity cannot be maintained unless all jobs accessing the data set in a cross-system environment specify DISP=SHR
I think that maybe because high-used RBA have not been changed for this vsam was hold by cics.Then the tool I use to check vsam data is startool,is it possible that STARTOOL treat the record which the high-used RBA point to as the last record?So it did not get the record after this record?
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