Hibernate.orgCommunity Documentation
This section explains some low level tricks to keep your indexes at peak performance. We cover some Lucene details which in most cases you don't have to know about: Hibernate Search will handle these operations optimally and transparently in most cases without the need for further configuration. Still, it is good to know that there are ways to configure the behaviour, if the need arises.
The index is physically stored in several smaller segments. Each segment is immutable and represents a generation of index writes. Index segments are periodically compacted, both to merge smaller segments and to remove stale entries; this merging process happens constantly in the background and can be tuned with the options specified in Section 3.6, “Tuning Lucene indexing performance”, but you can also define policies to fully run index optimizations when it is most suited for your specific workload.
With older versions of Lucene it was important to frequently optimize the index to maintain good performance, but with current Lucene versions this doesn't apply anymore. The benefit of explicit optimization is very low, and in certain cases even counter-productive. During an explicit optimization the whole index is processed and rewritten inflicting a significant performance cost. Optimization is for this reason a double-edged sword.
Another reason to avoid optimizing the index too often is that an optimization will, as a side effect, invalidate cached filters and field caches and internal buffers need to be refreshed.
Optimizing the index is often not needed, does not benefit write (update) performance at all, and is a slow operation: make sure you need it before activating it.
Of course optimizing the index does not only present drawbacks: after
the optimization process is completed and new
IndexReader
instances have loaded their buffers,
queries will perform at peak performance and you will have reclaimed all
disk space potentially used by stale entries.
It is recommended to not schedule any optimization, but if you wish to perform it periodically you should run it:
on an idle system or when the searches are less frequent
after a lot of index modifications
When using a MassIndexer
(see Section 6.3.2, “Using a MassIndexer”) it will optimize involved indexes
by default at the start and at the end of processing; you can change this
behavior by using
MassIndexer
.optimizeAfterPurge
and
MassIndexer
.optimizeOnFinish
respectively. The initial optimization is actually very cheap as it is
performed on an emtpy index: its purpose is to release the storage space
occupied by the old index.
While in most cases this is not needed, Hibernate Search can automatically optimize an index after:
a certain amount of write operations
or after a certain amount of transactions
The configuration for automatic index optimization can be defined on a global level or per index:
Example 7.1. Defining automatic optimization parameters
hibernate.search.default.optimizer.operation_limit.max = 1000 hibernate.search.default.optimizer.transaction_limit.max = 100 hibernate.search.Animal.optimizer.transaction_limit.max = 50
With the above example an optimization will be triggered to the
Animal
index as soon as either:
the number of additions and deletions reaches 1000
the number of transactions reaches 50
(hibernate.search.Animal.optimizer.transaction_limit.max
having priority over
hibernate.search.default.optimizer.transaction_limit.max
)
If none of these parameters are defined, no optimization is processed automatically.
The default implementation of OptimizerStrategy can be overriden by
implementing
org.hibernate.search.store.optimization.OptimizerStrategy
and setting the optimizer.implementation
property to
the fully qualified name of your implementation. This implementation must
implement the interface, be a public class and have a public constructor
taking no arguments.
Example 7.2. Loading a custom OptimizerStrategy
hibernate.search.default.optimizer.implementation = com.acme.worlddomination.SmartOptimizer hibernate.search.default.optimizer.SomeOption = CustomConfigurationValue hibernate.search.humans.optimizer.implementation = default
The keyword default
can be used to select the
Hibernate Search default implementation; all properties after the
.optimizer
key separator will be passed to the
implementation's initialize
method at
start.
You can programmatically optimize (defragment) a Lucene index from
Hibernate Search through the SearchFactory
:
Example 7.3. Programmatic index optimization
FullTextSession fullTextSession = Search.getFullTextSession(regularSession);
SearchFactory searchFactory = fullTextSession.getSearchFactory();
searchFactory.optimize(Order.class);
// or
searchFactory.optimize();
The first example optimizes the Lucene index holding
Order
s; the second, optimizes all indexes.
searchFactory.optimize()
has no effect on a JMS
or JGroups backend: you must apply the optimize operation on the Master
node.
The Lucene index is constantly being merged in the background to keep a good balance between write and read performance; in a sense this is a form of background optimization which is always applied.
The following match attributes of Lucene's IndexWriter
and are commonly used to tune how often merging occurs and how aggressive it is
applied. They are exposed by Hibernate Search via:
hibernate.search.[default|<indexname>].indexwriter.max_buffered_docs
hibernate.search.[default|<indexname>].indexwriter.max_merge_docs
hibernate.search.[default|<indexname>].indexwriter.merge_factor
hibernate.search.[default|<indexname>].indexwriter.ram_buffer_size
hibernate.search.[default|<indexname>].indexwriter.term_index_interval
See Section 3.6, “Tuning Lucene indexing performance” for a description of these properties.