The changes related to indices are as follows:
- By default, each index in Elasticsearch is allocated 1 primary shard and 1 replica.
- The colon (:) is no longer a valid character in the index name anymore due to the cross-cluster search support.
- Negative values for index.unassigned.node_left.delayed_timeout settings are treated as zero.
- The undocumented side effects from a _flush or a _force_merge operation have been fixed.
- The difference between max_ngram and min_ngram in NGramTokenFilter and NGramTokenizer is limited to 1 before. This default limit can be changed with the index.max_ngram_diff index setting. If the limit is exceeded, it will fail with an exception.
- The difference between max_shingle_size and min_shingle_size ...