The Elasticsearch Reindex API is a powerful way to index a subset of data from existing data. If you think of a long term statistics solution, you can aggregate data and store the aggregated values instead the atomic details. In my company we have an index that contains approximately 150 fields in each document. For a longterm solution only 30 are relevant. The Reindex API can just fetch the 30 desired fields and store them in a new index.
The reindex template
If you track your jekyll post with git, preferably if you hosting your github pages, than you can utilize the git attributes to automatically update post meta-data. For instance we replace the modified information in the
yaml frontmatter (that is the jekyll metadata) every time you do a update on a jekyll post or page.