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| <title>Cocoon Source Resolving</title> |
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| <meta content="Sylvain Wallez" name="DC.Creator"> |
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| <h1>The Store Components in Cocoon</h1> |
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| <p> |
| To keep cached data, Cocoon uses components implementing the |
| <em>org.apache.excalibur.Store</em> interface. Cocoon uses two |
| implementations of this interface, the "transient store" and the "store", |
| and optionally a third one, the "persistent store". |
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| <h2>The Transient store</h2> |
| <p> |
| The transient store (role <em>Store.TRANSIENT_STORE</em> is used for objects |
| that are not serializable, or whose storage doesn't make sense across server |
| restart. The transient store lives on its own and has no relation with other |
| stores. This is a mandatory component within Cocoon (i.e. used by Cocoon's code). |
| Transient store can drop stored components if system is running low on memory. |
| </p> |
| <p> |
| Cocoon uses the transient store to cache XSLT style sheets, XSP logicsheets, etc. |
| </p> |
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| <h2>The Store (aka "main Store")</h2> |
| <p> |
| The store (role <em>Store.ROLE</em>) can hold not serializable objects also. |
| It is a mandatory component, as the transient store. If memory is scarce, the |
| store can drop non serializable objects, and swaps serializable objects to disk. |
| For efficiency reasons, implementations of the store should swap out (or drop) |
| least often used objects. On shutdown, store can write out all objects residing |
| in memory to the disk. |
| </p> |
| <p> |
| Cocoon uses the main store to cache pipeline output. |
| </p> |
| |
| <h2>Persistent store (optional)</h2> |
| <p> |
| Some store (<em>Store.ROLE</em>) implementations (but not all) |
| may actually be just an in-memory cache that swap objects by calling |
| the persistent store (<em>Store.PERSISTENT_STORE</em>) when needed. So |
| the persistent store is an <em>optional</em> component which is used only |
| by MRUMemoryStore, and nowhere else in the code. |
| </p> |
| <p> |
| Two examples to illustrate this: |
| </p> |
| <ul> |
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| <li>when using JISP, we had this mechanism : the store was a MRUMemoryStore |
| swapping to the persistent store which was a JISPStore.</li> |
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| <li>JCS has its own in-memory front end to its own persistent storage. |
| In this configuration Store.ROLE will be a JCSStore and |
| Store.PERSISTENT_STORE will have no implementation, because we don't |
| need it. |
| </li> |
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| </ul> |
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| <h1>Summary</h1> |
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| <ul> |
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| <li>Store.TRANSIENT_STORE : used by Cocoon to store non-serializable objects</li> |
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| <li>Store.ROLE : used by Cocoon to store serializable objects</li> |
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| <li>Store.PERSISTENT_STORE : optional component that may be used by in-memory |
| implementations of Store.ROLE to delegate persistent storage.</li> |
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| </ul> |
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