Multiple Indexes¶
Much like Django’s multiple database support, Haystack has “multiple index” support. This allows you to talk to several different engines at the same time. It enables things like master-slave setups, multiple language indexing, separate indexes for general search & autocomplete as well as other options.
Specifying Available Connections¶
You can supply as many backends as you like, each with a descriptive name. A complete setup that accesses all backends might look like:
HAYSTACK_CONNECTIONS = {
'default': {
'ENGINE': 'haystack.backends.solr_backend.SolrEngine',
'URL': 'http://localhost:9001/solr/default',
'TIMEOUT': 60 * 5,
'INCLUDE_SPELLING': True,
'BATCH_SIZE': 100,
'SILENTLY_FAIL': True,
},
'autocomplete': {
'ENGINE': 'haystack.backends.whoosh_backend.WhooshEngine',
'PATH': '/home/search/whoosh_index',
'STORAGE': 'file',
'POST_LIMIT': 128 * 1024 * 1024,
'INCLUDE_SPELLING': True,
'BATCH_SIZE': 100,
'SILENTLY_FAIL': True,
},
'slave': {
'ENGINE': 'xapian_backend.XapianEngine',
'PATH': '/home/search/xapian_index',
'INCLUDE_SPELLING': True,
'BATCH_SIZE': 100,
'SILENTLY_FAIL': True,
},
'db': {
'ENGINE': 'haystack.backends.simple_backend.SimpleEngine',
'SILENTLY_FAIL': True,
}
}
You are required to have at least one connection listed within
HAYSTACK_CONNECTIONS
, it must be named default
& it must have a valid
ENGINE
within it.
Management Commands¶
All management commands that manipulate data use ONLY one connection at a
time. By default, they use the default
index but accept a --using
flag
to specify a different connection. For example:
./manage.py rebuild_index --noinput --using=whoosh
Automatic Routing¶
To make the selection of the correct index easier, Haystack (like Django) has the concept of “routers”. All provided routers are checked whenever a read or write happens, in the order in which they are defined.
For read operations (when a search query is executed), the for_read
method
of each router is called, until one of them returns an index, which is used for
the read operation.
For write operations (when a delete or update is executed), the for_write
method of each router is called, and the results are aggregated. All of the
indexes that were returned are then updated.
Haystack ships with a DefaultRouter
enabled. It looks like:
class DefaultRouter(BaseRouter):
def for_read(self, **hints):
return DEFAULT_ALIAS
def for_write(self, **hints):
return DEFAULT_ALIAS
This means that the default index is used for all read and write operations.
If the for_read
or for_write
method doesn’t exist or returns None
,
that indicates that the current router can’t handle the data. The next router
is then checked.
The for_write
method can return either a single string representing an
index name, or an iterable of such index names. For example:
class UpdateEverythingRouter(BaseRouter):
def for_write(self, **hints):
return ('myindex1', 'myindex2')
The hints
passed can be anything that helps the router make a decision. This
data should always be considered optional & be guarded against. At current,
for_write
receives an index
option (pointing to the SearchIndex
calling it) while for_read
may receive models
(being a list of Model
classes the SearchQuerySet
may be looking at).
You may provide as many routers as you like by overriding the
HAYSTACK_ROUTERS
setting. For example:
HAYSTACK_ROUTERS = ['myapp.routers.MasterRouter', 'myapp.routers.SlaveRouter', 'haystack.routers.DefaultRouter']
Master-Slave Example¶
The MasterRouter
& SlaveRouter
might look like:
from haystack import routers
class MasterRouter(routers.BaseRouter):
def for_write(self, **hints):
return 'master'
def for_read(self, **hints):
return None
class SlaveRouter(routers.BaseRouter):
def for_write(self, **hints):
return None
def for_read(self, **hints):
return 'slave'
The observant might notice that since the methods don’t overlap, this could be
combined into one Router
like so:
from haystack import routers
class MasterSlaveRouter(routers.BaseRouter):
def for_write(self, **hints):
return 'master'
def for_read(self, **hints):
return 'slave'
Manually Selecting¶
There may be times when automatic selection of the correct index is undesirable, such as when fixing erroneous data in an index or when you know exactly where data should be located.
For this, the SearchQuerySet
class allows for manually selecting the index
via the SearchQuerySet.using
method:
from haystack.query import SearchQuerySet
# Uses the routers' opinion.
sqs = SearchQuerySet().auto_query('banana')
# Forces the default.
sqs = SearchQuerySet().using('default').auto_query('banana')
# Forces the slave connection (presuming it was setup).
sqs = SearchQuerySet().using('slave').auto_query('banana')
Warning
Note that the models a SearchQuerySet
is trying to pull from must all come
from the same index. Haystack is not able to combine search queries against
different indexes.
Custom Index Selection¶
If a specific backend has been selected, the SearchIndex.index_queryset
and
SearchIndex.read_queryset
will receive the backend name, giving indexes the
opportunity to customize the returned queryset.
For example, a site which uses separate indexes for recent items and older
content might define index_queryset
to filter the items based on date:
def index_queryset(self, using=None):
qs = Note.objects.all()
archive_limit = datetime.datetime.now() - datetime.timedelta(days=90)
if using == "archive":
return qs.filter(pub_date__lte=archive_limit)
else:
return qs.filter(pub_date__gte=archive_limit)
Multi-lingual Content¶
Most search engines require you to set the language at the index level. For example, a multi-lingual site using Solr can use multiple cores and corresponding Haystack backends using the language name. Under this scenario, queries are simple:
sqs = SearchQuerySet.using(lang).auto_query(…)
During index updates, the Index’s index_queryset
method will need to filter
the items to avoid sending the wrong content to the search engine:
def index_queryset(self, using=None):
return Post.objects.filter(language=using)