The work for Solr-1045 patch started with a goal to achieve index generation/building using the Apache MapReduce task. Solr-1045 patch converts all the input records to a set of <key, value> pairs in each map task that runs on Hadoop. Further it goes on creating SolrInputDocument
from the <key, value>, and later creating the Solr indexes. The following diagram depicts this process:
Reduce tasks can be used to perform deduplication of indexes, and merge them together if required. Although merge index seems to be an interesting feature, it is actually a costly affair in terms of processing, and you will not find many implementations with merge index functionality. Once the indexes are created, you can load them on your Solr instance and use them for searching.
You can download this particular patch from https://issues.apache.org/jira/browse/SOLR-1045, and patch your Solr instance. To apply a patch to your Solr instance, you need to first...