I did an upgrade of my elasticsearch instance from elasticsearch-2.x to elasticearch-5.6 . Everything seems to work fine. But before i do an upgrade to version 6, I have to reindex data. Whats does reindexing mean?
I have a script that is creating all data i need on elasticsearch. Do i have to start this script. But in this case it would be the same like i would remove all indices and install all dumps back into elasticsearch.
I dont know how to try this because i dont know the "right way" to do it.
EDIT I did now found the api with _reindex post. Do i have to do this for all indexes i have or is there an application i don't know that is doing this maybe faster than me :-)
First, why is this necessary: Behind the scenes Apache Lucene is writing the data. Lucene can always write its current version and read the previous one.
If you have upgraded from 2.x, you need to make sure that all the data has been written with Lucene 6 before you can upgrade to Elasticsearch 6.x. You can actually check this in the version information of all the Lucene segments with GET /_segments (this might give you a lot of information).
What you want to run to get this done is the reindex in place. And I can highly recommend the free X-Pack Basic migration assistant to make sure you have upgraded all indices and don't have any other hidden upgrade problems.