Search Results: hudders

Operating Systems

Aug 1 ’09

A major new CICS performance issue is the Task Control Block (TCB) switching required to access VSAM data sets when supporting threadsafe applications running DB2. Prior to the announcement of VSAM threadsafe support in CICS Transaction Server (TS) V3R2, any threadsafe application running on an L8 or L9 TCB would have to do a TCB switch to the Quasi-Reentrant (QR) to service the VSAM request because file control wasn’t threadsafe code. Unfortunately, although VSAM threadsafe was announced with CICS TS V3R2, only the Record-Level Sharing (RLS) portion was available at general availability of the product.…

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Operating Systems

Dec 2 ’08

A question often asked regarding VSAM is: When should you reorganize a VSAM data set? Many recommendations related to VSAM reorganization can be misleading and confusing. Unnecessarily reorganizing VSAM data sets can waste resources, but not reorganizing VSAM data sets also can result in longer processing times that may represent lost resources. This article explores reasons for reorganizing a VSAM data set, specifically a KSDS (Key-Sequenced Data Set), and tries to provide guidelines to apply to this important decision process. Note that the reorganization guidelines presented here vary on whether the data set is processed online (e.g., CICS…

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CICS / WebSphere

Dec 1 ’08

A Shared Data Table (SDT) is simply a VSAM Key Sequenced Data Set (KSDS) that has been loaded into virtual storage and accessed as a table— reducing physical I/O and improving response time. The feature for using SDTs has been available in CICS TS since CICS/ESA 3.3, but SDT use has been somewhat limited in many installations for several reasons:

  • The amount of real storage required to support data sets defined as SDTs
  • The recommendation that SDTs be used for data sets that reflect a high read-to-write activity ratio or…
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Operating Systems

Jul 1 ’08

This article examines several areas fthat should be considered when ftuning Local Shared Resource (LSR) pools. The main performance objective when tuning CICS LSR pools is to improve the lookaside hit ratios, but there are other tuning areas that are generally overlooked. In this article, we will attempt to answer the questions asked in many CICS tuning classes such as:

• How many pools should I define?

• Are there any advantages to defining multiple pools?

• How many strings should I define?

• How do I know when a file…

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Applications & Integrations

Mar 1 ’08

CICS TS 3.2 became available at the end of June 2007. This release has many interesting features, including the first attempt to support data structures above the bar. Initially, the 64-bit support is for channel/container data that will be stored above the bar. Access to storage above the bar lets the CICS TS user store and access a significantly greater amount of virtual storage without limiting the amount of data to be stored in containers. However, this storage does require backing by real storage space when used; therefore, care must be taken not to overcommit the amount of real storage,…

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CICS / WebSphere

Oct 1 ’05

The correct allocation of strings to files is an important tuning opportunity. Under-allocating the number of strings assigned can result in short on string conditions that adversely affect response times and could also delay transactions despite the availability of other resources such as CPU and virtual or real storage. Over-allocating strings can waste storage for Non-Shared Resource (NSR) files because each string requires a data buffer and, in the case of a Keyed Sequence Data Set (KSDS), you’d also need an index buffer. The unnecessary strings waste storage that could otherwise improve performance of another file or…

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CICS / WebSphere

Jun 1 ’05

Tuning Temporary Storage (TS) has become important in CICS systems; it requires attention in regions where it’s heavily used. TS comes in two flavors:

  • TS MAIN, where the information is maintained in the Extended CICS Dynamic Storage Area (ECDSA)
  • TS AUX, where the information is maintained in a VSAM file called DFHTEMP.

More applications are beginning to depend on TS and use it with permanent information that’s needed across CICS restarts. Somewhere along the line, the concept of TS was lost because it’s…

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CICS / WebSphere

Apr 1 ’05

Index CISZ is a largely neglected VSAM KSDS tuning area. Often, the VSAM default algorithms determine the index CISZ associated with the KSDS cluster. The default index VSAM selects is generally acceptable, especially after the change to the selection criteria in z/OS Version 1 Release 3. Tuning the index CISZ is an important issue because of:

-        The number of index levels associated with the file

-        The need to avoid key compression problems.

This article reviews the selection of…

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CICS / WebSphere

Feb 1 ’05

There are several ways to handle VSAM files in CICS/TS using different buffering techniques. The more common buffering technique is Local Shared Resources (LSR), where the file’s buffering is shared in a buffer pool. (We’ll review LSR in a future article.) Another alternative is Record Level Sharing (RLS), where the file’s buffering is handled by SMSVSAM in a separate region and data space. This article explores the tuning associated with Non-Shared Resource (NSR) files running under CICS, where the buffering is defined for the exclusive use of each file.

As…

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CICS / WebSphere

Dec 1 ’04

CICS has three Interval Control Values (ICVs) specified in the System Initialization Table (SIT), via overrides or through the use of CEMT command, that can be used to set a new value. Setting these parameters correctly can help reduce system CPU overhead and improve resource usage. This especially applies to installations with many CICS regions. This article explores these parameters and offers recommendations on what values to use. The three parameters we’ll focus on are:

  • ICV is used to specify the maximum time CICS is to wait when there’s no work…
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