53 lines
1.7 KiB
ReStructuredText
53 lines
1.7 KiB
ReStructuredText
============
|
|
Field caches
|
|
============
|
|
|
|
The default (``filedb``) backend uses *field caches* in certain circumstances.
|
|
The field cache basically pre-computes the order of documents in the index to
|
|
speed up sorting and faceting.
|
|
|
|
Generating field caches can take time the first time you sort/facet on a large
|
|
index. The field cache is kept in memory (and by default written to disk when it
|
|
is generated) so subsequent sorted/faceted searches should be faster.
|
|
|
|
The default caching policy never expires field caches, so reused searchers and/or
|
|
sorting a lot of different fields could use up quite a bit of memory with large
|
|
indexes.
|
|
|
|
|
|
Customizing cache behaviour
|
|
===========================
|
|
|
|
(The following API examples refer to the default ``filedb`` backend.)
|
|
|
|
*By default*, Whoosh saves field caches to disk. To prevent a reader or searcher
|
|
from writing out field caches, do this before you start using it::
|
|
|
|
searcher.set_caching_policy(save=False)
|
|
|
|
By default, if caches are written to disk they are saved in the index directory.
|
|
To tell a reader or searcher to save cache files to a different location, create
|
|
a storage object and pass it to the ``storage`` keyword argument::
|
|
|
|
from whoosh.filedb.filestore import FileStorage
|
|
|
|
mystorage = FileStorage("path/to/cachedir")
|
|
reader.set_caching_policy(storage=mystorage)
|
|
|
|
|
|
Creating a custom caching policy
|
|
================================
|
|
|
|
Expert users who want to implement a custom caching policy (for example, to add
|
|
cache expiration) should subclass :class:`whoosh.filedb.fieldcache.FieldCachingPolicy`.
|
|
Then you can pass an instance of your policy object to the ``set_caching_policy``
|
|
method::
|
|
|
|
searcher.set_caching_policy(MyPolicy())
|
|
|
|
|
|
|
|
|
|
|
|
|