Author: thomasm
Date: Wed Feb 25 16:48:52 2015
New Revision: 1662257
URL: http://svn.apache.org/r1662257
Log:
OAK-301 : oak documentation
Added:
jackrabbit/oak/trunk/oak-doc/src/site/markdown/nodestore/persistent-cache.md
Added:
jackrabbit/oak/trunk/oak-doc/src/site/markdown/nodestore/persistent-cache.md
URL:
http://svn.apache.org/viewvc/jackrabbit/oak/trunk/oak-doc/src/site/markdown/nodestore/persistent-cache.md?rev=1662257&view=auto
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jackrabbit/oak/trunk/oak-doc/src/site/markdown/nodestore/persistent-cache.md
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jackrabbit/oak/trunk/oak-doc/src/site/markdown/nodestore/persistent-cache.md
Wed Feb 25 16:48:52 2015
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+<!--
+ Licensed to the Apache Software Foundation (ASF) under one or more
+ contributor license agreements. See the NOTICE file distributed with
+ this work for additional information regarding copyright ownership.
+ The ASF licenses this file to You under the Apache License, Version 2.0
+ (the "License"); you may not use this file except in compliance with
+ the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+ Unless required by applicable law or agreed to in writing, software
+ distributed under the License is distributed on an "AS IS" BASIS,
+ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ See the License for the specific language governing permissions and
+ limitations under the License.
+ -->
+
+## Persistent Cache
+
+The document storage optionally uses the persistent cache.
+The cache acts like an in-memory cache for old revisions,
+but in addition to keeping the most recently used nodes in memory,
+it also stores them to disk. That way, many reads from the storage backend
(for example MongoDB)
+are replaced by reads from the local disk. This is specially useful if reads
from the local disk
+are faster than reads from the storage backend. In addition to that, the
persistent cache reduces
+the load on the storage backend.
+
+###Â OSGi Configuration
+
+The OSGi configuration of the persistent cache is:
+
+ org.apache.jackrabbit.oak.plugins.document.DocumentNodeStoreService
+ persistentCache=./cache
+
+This will enable the persistent cache, and set the configuration option to
"./cache".
+
+### Configuration Options
+
+The persistent cache configuration setting is string with a number of comma
separated elements.
+The first element is the directory where the cache is stored. Example:
+
+ ./cache
+
+In this case, the data is stored in the directory "cache",
+relative to the current working directory.
+By default, there are at most two files (two generations) with the name
"cache-x.data",
+where x is an incrementing number (0, 1,...).
+A file is at most 1 GB by default.
+If the file is larger, the next file is created, and if there are more than
two files,
+the oldest one is removed.
+If data from the older file is accessed, it is copied to the latest file.
+That way, data that is not recently read will eventually be removed.
+
+The following other configuration options are available:
+
+* Size. A file is at most 1 GB by default. To change maximum size of a file,
+use "size=x", where x is the size in MB.
+
+* Binary caching. When using the BlobStore,
+binaries smaller than 1 MB are stored in the persistent cache by default.
+The maximum size can be changed using the setting "binary=x",
+where x is the size in bytes. To disable the binary cache, use "binary=0".
+
+* Node caching. By default, nodes at all revisions are cached.
+To disable this option, use "-nodes".
+
+* Children caching. By default, the list of children of a node is cached.
+To disable this option, use "-children".
+
+* Diff caching. By default, the list of differences between two
+revisions is cached. To disable this option, use "-diff".
+
+* Compaction. By default, when a cache file is closed,
+it is compacted and compressed (at a rate of around 100 MB per second).
+That way, the disk space is used more efficiently.
+To disable this option, use "-compact".
+
+* Compression. By default, the cache is compressed, saving space.
+To disable this option, use "-compress".
+
+Those setting can be appended to the persistent cache configuration string.
+An example configuration is:
+
+ ./cache,size=2048,binary=0,-compact,-compress
+
+###Â Dependencies
+
+Internally, the persistent cache uses a key-value store
+(basically a java.util.Map), which is persisted to disk.
+The current key-value store backend is the [H2
MVStore](http://www.h2database.com/html/mvstore.html).
+This library is only needed if the persistent cache is configured.
+Version 1.4.185 or newer is needed.
+
+ <dependency>
+ <groupId>com.h2database</groupId>
+ <artifactId>h2-mvstore</artifactId>
+ <version>1.4.185</version>
+ </dependency>
+
+
+
