Apache Solr Reference Guide Covering Apache Solr 6.0

Document Centric Versioning Constraints
Optimistic Concurrency is extremely powerful, and works very efficiently because it uses an internally assigned,
globally unique values for the _version_ field. However, In some situations users may want to configure their
own document specific version field, where the version values are assigned on a per-document basis by an
external system, and have Solr reject updates that attempt to replace a document with an "older" version. In
situations like this the DocBasedVersionConstraintsProcessorFactory can be useful.
The basic usage of DocBasedVersionConstraintsProcessorFactory is to configure it in solrconfig.x
ml as part of the UpdateRequestProcessorChain and specify the name of your custom versionField in your
schema that should be checked when validating updates:
my_version_l
Once configured, this update processor will reject (HTTP error code 409) any attempt to update an existing
document where the value of the my_version_l field in the "new" document is not greater then the value of
that field in the existing document.
versionField vs _version_
The _version_ field used by Solr for its normal optimistic concurrency also has important semantics in
how updates are distributed to replicas in SolrCloud, and MUST be assigned internally by Solr. Users
can not re-purpose that field and specify it as the versionField for use in the DocBasedVersionCo
nstraintsProcessorFactory configuration.
DocBasedVersionConstraintsProcessorFactory supports two additional configuration params which are
optional:
ignoreOldUpdates - A boolean option which defaults to false. If set to true then instead of rejecting
updates where the versionField is too low, the update will be silently ignored (and return a status 200
to the client).
deleteVersionParam - A String parameter that can be specified to indicate that this processor should
also inspect Delete By Id commands. The value of this configuration option should be the name of a
request parameter that the processor will now consider mandatory for all attempts to Delete By Id, and
must be be used by clients to specify a value for the versionField which is greater then the existing
value of the document to be deleted. When using this request param, any Delete By Id command with a
high enough document version number to succeed will be internally converted into an Add Document
command that replaces the existing document with a new one which is empty except for the Unique Key
and versionField to keeping a record of the deleted version so future Add Document commands will
fail if their "new" version is not high enough.
Please consult the processor javadocs and test configs for additional information and example usages.
De-Duplication
Preventing duplicate or near duplicate documents from entering an index or tagging documents with a
signature/fingerprint for duplicate field collapsing can be efficiently achieved with a low collision or fuzzy hash
algorithm. Solr natively supports de-duplication techniques of this type via the class and allows
for the easy addition of new hash/signature implementations. A Signature can be implemented several ways:
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