6.6 DynaCache tuning
Tuning DynaCache is much like tuning any other performance-enhancing component: it is an iterative process. It should begin at application design, with guidance from the application architect on what should and should not be cached based on input from the requirement stage and knowledge of the application scenarios.
This process is further refined through the development, validation, and production phase of the project. It is invaluable during validation and pre-production phases of development to monitor performance changes so as to understand and rectify the impact of cache policies and tuning on system behavior.
You need to run some projected workload without caching to determine values such as the cost of generating the object, although you may choose to rely on the intuition and experience of the application architect.
Guidelines for determining the effectiveness of caching should take into account the following:
| The cost of generating a response should be greater than the maximum cache access time, where the maximum cache access time should factor in overhead for disk access, distribution policy, and so on. |
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| The lower the validity of the object and response, the more likely that it will not be reused. This can result in larger latencies due to cache misses and cleanup overhead, than simply not caching the object. |
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| The objects with more popularity and business value should be assigned a higher relative priority. |
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| The higher the degree of connectivity of an object, the more costly it is to invalidate and evict the object from the cache. Take this into account when determining where to cache the object in terms of keeping it in the memory cache, disk cache, or distributing the object across the cluster. |
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| The DynaCache specification provides attributes that can be used to declare properties of the cached object such as timeout (in seconds), priority (LOWEST PRIORITY = 0, DEFAULT PRIOIRTY = 3, HIGHEST PRIORITY = 16), and inactivity, to affect the treatment of these cached objects. |