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