This article is to explain how solr cache works.
Please also refer to http://wiki.apache.org/solr/SolrCaching.
How does cache works? When does it expire?
Solr caches are associated with an Index Searcher — a particular ‘view’
of the index that doesn’t change. So as long as that Index Searcher is
being used, any items in the cache will be valid and available for
reuse. Caching in Solr is unlike ordinary caches in that Solr cached
objects will not expire after a certain period of time; rather, cached objects will be valid as long as the Index Searcher is valid.
How does a new index searcher start to work?
The current Index Searcher serves requests and when a new searcher is
opened, the new one is auto-warmed while the current one is still
serving external requests. When the new one is ready, it will be
registered as the current searcher and will handle any new search
requests. The old searcher will be closed after all request it was
servicing finish. The current Searcher is used as the source of
auto-warming. When a new searcher is opened, its caches may be
prepopulated or “autowarmed” using data from caches in the old searcher.
| Cache Type |
Filter Cache |
Query Result Cache |
Document Cache |
| Description |
This cache stores unordered sets of document IDs |
This cache stores ordered sets of document IDs — results of a query ordered by some criteria. |
The documentCache stores Lucene Document objects that have been fetched from disk. |
| Key |
basic query, filter query treated as different keys |
org.apache.solr.search.QueryResultKey, including basic query, sort fields, filter(as a Query object), and nc_flags |
Solr Doc Unique Id |
| Value |
org.apache.solr.search.HashDocSet |
org.apache.solr.search.DocSlice |
doc |
| Purpose |
First, the filter cache stores the results of any filter queries (“fq” parameters) that Solr is explicitly asked to execute. (Each filter
is executed and cached separately. When it’s time to use them to limit
the number of results returned by a query, this is done using set
intersections.) |
for the same query, no need execute query again |
no need fetch from disk again, if it is already in cache |
| Purpose2 |
Second,
the filter cache is used for faceting in some cases. (In particular,
when the TermEnum method is used, a filterCache entry is added for each
term tested.) |
N/A |
N/A |
| Purpose3 |
Finally, the filter cache may be used for sorting if the config option is set to true in solfconfig.xml. |
N/A |
N/A |
| queryResultWindowSize impact to cache |
N/A |
When
a search is requested, a superset of the requested number of document
ids are collected. For example, of a search for a particular query
requests matching documents 10 through 19, and queryWindowSize is 50,
then documents 0 through 50 will be collected and cached. Any further
requests in that range can be satisfied via the cache. |
N/A |
posted on 2008-11-11 15:05
Justin Chen 阅读(1699)
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