[[index-modules-store]] == Store The store module allows you to control how index data is stored and accessed on disk. [float] [[file-system]] === File system storage types There are different file system implementations or _storage types_. By default, Elasticsearch will pick the best implementation based on the operating environment. This can be overridden for all indices by adding this to the `config/elasticsearch.yml` file: [source,yaml] --------------------------------- index.store.type: niofs --------------------------------- It is a _static_ setting that can be set on a per-index basis at index creation time: [source,console] --------------------------------- PUT /my_index { "settings": { "index.store.type": "niofs" } } --------------------------------- WARNING: This is an expert-only setting and may be removed in the future. The following sections lists all the different storage types supported. `fs`:: Default file system implementation. This will pick the best implementation depending on the operating environment, which is currently `hybridfs` on all supported systems but is subject to change. [[simplefs]]`simplefs`:: The Simple FS type is a straightforward implementation of file system storage (maps to Lucene `SimpleFsDirectory`) using a random access file. This implementation has poor concurrent performance (multiple threads will bottleneck). It is usually better to use the `niofs` when you need index persistence. [[niofs]]`niofs`:: The NIO FS type stores the shard index on the file system (maps to Lucene `NIOFSDirectory`) using NIO. It allows multiple threads to read from the same file concurrently. It is not recommended on Windows because of a bug in the SUN Java implementation. [[mmapfs]]`mmapfs`:: The MMap FS type stores the shard index on the file system (maps to Lucene `MMapDirectory`) by mapping a file into memory (mmap). Memory mapping uses up a portion of the virtual memory address space in your process equal to the size of the file being mapped. Before using this class, be sure you have allowed plenty of <>. [[hybridfs]]`hybridfs`:: The `hybridfs` type is a hybrid of `niofs` and `mmapfs`, which chooses the best file system type for each type of file based on the read access pattern. Currently only the Lucene term dictionary, norms and doc values files are memory mapped. All other files are opened using Lucene `NIOFSDirectory`. Similarly to `mmapfs` be sure you have allowed plenty of <>. [[allow-mmap]] You can restrict the use of the `mmapfs` and the related `hybridfs` store type via the setting `node.store.allow_mmap`. This is a boolean setting indicating whether or not memory-mapping is allowed. The default is to allow it. This setting is useful, for example, if you are in an environment where you can not control the ability to create a lot of memory maps so you need disable the ability to use memory-mapping. === Pre-loading data into the file system cache NOTE: This is an expert setting, the details of which may change in the future. By default, Elasticsearch completely relies on the operating system file system cache for caching I/O operations. It is possible to set `index.store.preload` in order to tell the operating system to load the content of hot index files into memory upon opening. This setting accept a comma-separated list of files extensions: all files whose extension is in the list will be pre-loaded upon opening. This can be useful to improve search performance of an index, especially when the host operating system is restarted, since this causes the file system cache to be trashed. However note that this may slow down the opening of indices, as they will only become available after data have been loaded into physical memory. This setting is best-effort only and may not work at all depending on the store type and host operating system. The `index.store.preload` is a static setting that can either be set in the `config/elasticsearch.yml`: [source,yaml] --------------------------------- index.store.preload: ["nvd", "dvd"] --------------------------------- or in the index settings at index creation time: [source,console] --------------------------------- PUT /my_index { "settings": { "index.store.preload": ["nvd", "dvd"] } } --------------------------------- The default value is the empty array, which means that nothing will be loaded into the file-system cache eagerly. For indices that are actively searched, you might want to set it to `["nvd", "dvd"]`, which will cause norms and doc values to be loaded eagerly into physical memory. These are the two first extensions to look at since Elasticsearch performs random access on them. A wildcard can be used in order to indicate that all files should be preloaded: `index.store.preload: ["*"]`. Note however that it is generally not useful to load all files into memory, in particular those for stored fields and term vectors, so a better option might be to set it to `["nvd", "dvd", "tim", "doc", "dim"]`, which will preload norms, doc values, terms dictionaries, postings lists and points, which are the most important parts of the index for search and aggregations. Note that this setting can be dangerous on indices that are larger than the size of the main memory of the host, as it would cause the filesystem cache to be trashed upon reopens after large merges, which would make indexing and searching _slower_.