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HP OpenVMS System Manager's Manual, Volume 2:... |
Managing DECdtm Services |
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Later, you can change the size of a transaction log, or move it. However, careful planning at this stage reduces the need for future changes.
This section describes:
| Task | Section |
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Deciding the
size of a transaction log
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Deciding the Size of a Transaction Log
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Deciding the location of
a transaction log
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Deciding the Location of a Transaction Log
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Deciding
the Size of a Transaction Log
When you create a transaction log, you can specify its size.
The default size is 4000 blocks; this gives acceptable performance
on most systems.
If you know the expected rate of transactions, HP suggests the following formula to calculate the transaction log size:size = 40 × rate
where:
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size
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is the size of the transaction
log in blocks.
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rate
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is the average number of transactions
executed per second.
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If you do not know the rate of transactions, accept the default size of 4000 blocks.
Deciding
the Location of a Transaction Log
If possible, choose a disk that is:
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Fast
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Achieve speed by using a
high-performance disk, such as a solid-state disk, that is not heavily
used.
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Highly available
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Achieve high availability
by having multiple access paths to the data.
In an OpenVMS Cluster, use a disk that can be accessed by the other nodes in the cluster. This ensures that if one node fails, transactions running on other nodes are not blocked. |
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Reliable
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Achieve reliability by keeping multiple
copies of the data.
Using a shadowed disk is more reliable than using a nonshadowed disk, but may be slower because transaction logs are almost exclusively write-only. |
You may need to choose between speed and either availability or reliability. For example, if the node is a workstation, you may choose to sacrifice speed for availability and reliability by putting the node's transaction log on a shadowed HSC-based disk, instead of on a faster disk attached to the workstation.
In a cluster environment, try to distribute the transaction logs across different disks. Having more than one transaction log on a disk can lead to poor transaction performance.
 | Make sure that the disk has enough contiguous space to hold the transaction log. A discontiguous transaction log leads to poor transaction performance. |
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