Apache Solr Reference Guide Covering Apache Solr 6.0

Working with External Files and Processes
The ExternalFileField Type
Format of the External File
Reloading an External File
The PreAnalyzedField Type
JsonPreAnalyzedParser
SimplePreAnalyzedParser
The ExternalFileField Type
The ExternalFileField type makes it possible to specify the values for a field in a file outside the Solr index.
For such a field, the file contains mappings from a key field to the field value. Another way to think of this is that,
instead of specifying the field in documents as they are indexed, Solr finds values for this field in the external file.
External fields are not searchable. They can be used only for function queries or display. For more
information on function queries, see the section on Function Queries.
The ExternalFileField type is handy for cases where you want to update a particular field in many
documents more often than you want to update the rest of the documents. For example, suppose you have
implemented a document rank based on the number of views. You might want to update the rank of all the
documents daily or hourly, while the rest of the contents of the documents might be updated much less
frequently. Without ExternalFileField, you would need to update each document just to change the rank.
Using ExternalFileField is much more efficient because all document values for a particular field are stored
in an external file that can be updated as frequently as you wish.
In
schema.xml, the definition of this field type might look like this:
The keyField attribute defines the key that will be defined in the external file. It is usually the unique key for the
index, but it doesn't need to be as long as the keyField can be used to identify documents in the index. A defV
al defines a default value that will be used if there is no entry in the external file for a particular document.
The valType attribute specifies the actual type of values that will be found in the file. The type specified must be
either a float field type, so valid values for this attribute are pfloat, float or tfloat. This attribute can be
omitted.
Format of the External File
The file itself is located in Solr's index directory, which by default is $SOLR_HOME/data. The name of the file
should be external_ fieldname or external_ fieldname.*
. For the example above, then, the file could
be named external_entryRankFile or external_entryRankFile.txt.
If any files using the name pattern (such as ) appear, the last (after being sorted by name) will
.* .txt
be used and previous versions will be deleted. This behavior supports implementations on systems
where one may not be able to overwrite a file (for example, on Windows, if the file is in use).
The file contains entries that map a key field, on the left of the equals sign, to a value, on the right. Here are a
few example entries:
doc33=1.414
doc34=3.14159
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