I have a ~3m document (70GB) elastic index that I wish to reindex to an updated template mapping. I issue the basic reindex source -> destination REST call from kibana and it returns a task id. The designated task shows the correct number of documents that need to be reindexed into the new index. However the task completes with only a small fraction (6000 - approx 1/2 GB) of these actually reindexed. I have noticed this trouble on approximately 40% of my reindexes to varying degrees.
I cannot see what the issue may be on my side. The updated template is based on the source one save a few additional multifields therefore is type compatible.
What are the possible issues?
