NJBUFF parameter: Difference between revisions

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{{Template:NJBUFF parameter subtitle}}
==Summary==
==Summary==
<dl>
<dl>
<dt>Default value
<dt>Default value
<dd>The default for z/OS and z/VM is NSERVS + NSUBTKS + 1. The default for z/VSE is 1, because z/VSE does not support multiple journal buffers.  
<dd>The default for z/OS and z/VM is <code><var>[[NSERVS_parameter|NSERVS]]</var> + <var>[[NSUBTKS_parameter|NSUBTKS]]</var> + 1</code>. The default for z/VSE is 1, because z/VSE does not support multiple journal buffers.  
<dt>Parameter type
<dt>Parameter type
<dd>System
<dd>System
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<dd>
<dd>
<p>Cannot be reset</p>
<p>Cannot be reset</p>
<p>In z/OS, the NJBUFF parameter can be set explicitly only via the PARM field in the EXEC card. See the <var>Model&nbsp;204 System Manager's Guide</var>.</p>
<p>In z/OS, the <var>NJBUFF</var> parameter can be set explicitly only via the PARM field in the EXEC card. See [[Defining the runtime environment (CCAIN)#Specifying EXEC statement parameters|Specifying EXEC statement parameters]].</p>
<p>In z/VM, the NJBUFF parameter is stacked in the EXEC that issues all the FILEDEFs.</p>
<p>
In z/VM, the <var>NJBUFF</var> parameter is stacked in the EXEC that issues all the FILEDEFs.</p>
<dt>Related products
<dt>Related products
<dd>All
<dd>All
<dt>Introduced
<dt>Introduced
<dd><var class="product">Model 204 V6.1</var> or earlier
<dd><var class="product">Model 204 V2.1</var>  
</dl>
</dl>
==Description==
==Description==
<p>The NJBUFF parameter has a dual role of allocating the number of channel programs and journal buffers. </p>
<p>
<p>NJBUFF can be 1, or NSERVS + NSUBTKS + 1,  or any value larger than NSERVS + NSUBTKS + 1. Setting NJBUFF to a value greater than 1 invokes multiple journal buffers and ensures that a free buffer is always available for the journal. </p>
The <var>NJBUFF</var> parameter has a dual role of allocating the number of channel programs and journal buffers. </p>
<p>In z/OS only, the NJBUFF setting is automatically recalculated when the setting is greater than 1 and less than or equal to NSERVS + NSUBTKS + 1. The initial value of NJBUFF is used to define the number of concurrent I/O operations (NCP) for the journal data set. Sizing NJBUFF to the value calculated in the formula guarantees the optimal number of NCP for the journal data set. </p>
<p>
The NJBUFF parameter has the following options:
<var>NJBUFF</var> can be 1, or <code>NSERVS + NSUBTKS + 1</code>,  or any value larger than <code>NSERVS + NSUBTKS + 1</code>. Setting <var>NJBUFF</var> to a value greater than 1 invokes multiple journal buffers and ensures that a free buffer is always available for the journal. </p>
<p>
In z/OS only, the <var>NJBUFF</var> setting is automatically recalculated when the setting is greater than 1 and less than or equal to <code>NSERVS + NSUBTKS + 1</code>. The initial value of <var>NJBUFF</var> is used to define the number of channel programs (NCP) for the journal data set. Sizing <var>NJBUFF</var> to the value calculated in the formula guarantees the optimal number of NCP for the journal data set. </p>
The <var>NJBUFF</var> parameter has the following options:
<table>
<table>
<caption>NJBUFF parameter options</caption>
<caption>NJBUFF parameter options</caption>
<tr><th>NJBUFF=</th><th>Option</th></tr>
<tr class="head"><th>NJBUFF=</th><th>Option</th></tr>
<tr><th><var>0 or is omitted</var></th><td>The default value is used.</td></tr>
 
<tr><th align="right"><var>1</var></th><td>Only one buffer and one Network Control Program (NCP) is obtained. All puts and waits are synchronized. Recommended only when NUSER=1.</td></tr>
<tr><td>0 or is omitted</td><td>The default value is used.</td></tr>
<tr><th><var>NJBUFF is greater than NSERVS + NSUBTKS + 1</var></th><td>
 
<p>The specified number of buffers is obtained.</p>
<tr><td>1</td><td>Only one buffer and one channel program (NCP) is obtained. All puts and waits are synchronized. Recommended only when <var>[[NUSERS_parameter|NUSERS]]</var>=1.</td></tr>
 
<tr><td>Greater than <code>NSERVS + NSUBTKS + 1</code></td>
<td>The specified number of buffers is obtained.
<p>If the value is greater than 255 and 31-bit BSAM is allowed, only 255 NCPs are obtained.</p>
<p>If the value is greater than 255 and 31-bit BSAM is allowed, only 255 NCPs are obtained.</p>
<p>If 31-bit BSAM is not allowed, on 99 NCPs are obtained.</p>
<p>If 31-bit BSAM is not allowed, only 99 NCPs are obtained.</p>
<p>If the buffer number is larger than the NCPs, for example, NJBUFF=500, then 500 buffers are obtained, but only a maximum of NCP buffers are active. I/Os are checked only when they reach the NCP limit or when they are forced.</p>
<p>If the buffer number is larger than the NCPs, for example, <code>NJBUFF=500</code>, then 500 buffers are obtained, but only a maximum of NCP buffers are active. I/Os are checked only when they reach the NCP limit or when they are forced.</p>
</td></tr>
</td></tr>
<tr><th><var>For z/OS only: If NJBUFF is greater than one and less than or equal to NSERVS + NSUBTKS + 1.</var></th><td>
 
<p>The value is recalculated by <var class="product">Model&nbsp;204</var> as:</p>
<tr><td>For z/OS only: <br/>Greater than one and less than or equal to <code>NSERVS + NSUBTKS + 1</code>.</td>
<p>NJBUFF=NSERVS + NSUBTKS + 1</p>
<td>The value is recalculated by <var class="product">Model&nbsp;204</var> as: <code>NSERVS + NSUBTKS + 1</code>
<p>Message M204.0434 is issued.</p>
<p>Message <code>M204.0434</code> is issued.</p>
</td></tr>
</td></tr>
</table>
</table>
[[Category:System parameters]]
[[Category:System parameters]]
[[Category:Parameters]]
[[Category:Parameters]]

Latest revision as of 13:01, 25 August 2015

Number of journal buffers

Summary

Default value
The default for z/OS and z/VM is NSERVS + NSUBTKS + 1. The default for z/VSE is 1, because z/VSE does not support multiple journal buffers.
Parameter type
System
Where set

Cannot be reset

In z/OS, the NJBUFF parameter can be set explicitly only via the PARM field in the EXEC card. See Specifying EXEC statement parameters.

In z/VM, the NJBUFF parameter is stacked in the EXEC that issues all the FILEDEFs.

Related products
All
Introduced
Model 204 V2.1

Description

The NJBUFF parameter has a dual role of allocating the number of channel programs and journal buffers.

NJBUFF can be 1, or NSERVS + NSUBTKS + 1, or any value larger than NSERVS + NSUBTKS + 1. Setting NJBUFF to a value greater than 1 invokes multiple journal buffers and ensures that a free buffer is always available for the journal.

In z/OS only, the NJBUFF setting is automatically recalculated when the setting is greater than 1 and less than or equal to NSERVS + NSUBTKS + 1. The initial value of NJBUFF is used to define the number of channel programs (NCP) for the journal data set. Sizing NJBUFF to the value calculated in the formula guarantees the optimal number of NCP for the journal data set.

The NJBUFF parameter has the following options:

NJBUFF parameter options
NJBUFF=Option
0 or is omittedThe default value is used.
1Only one buffer and one channel program (NCP) is obtained. All puts and waits are synchronized. Recommended only when NUSERS=1.
Greater than NSERVS + NSUBTKS + 1 The specified number of buffers is obtained.

If the value is greater than 255 and 31-bit BSAM is allowed, only 255 NCPs are obtained.

If 31-bit BSAM is not allowed, only 99 NCPs are obtained.

If the buffer number is larger than the NCPs, for example, NJBUFF=500, then 500 buffers are obtained, but only a maximum of NCP buffers are active. I/Os are checked only when they reach the NCP limit or when they are forced.

For z/OS only:
Greater than one and less than or equal to NSERVS + NSUBTKS + 1.		 The value is recalculated by Model 204 as: NSERVS + NSUBTKS + 1

Message M204.0434 is issued.

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