Too many fields bad for elasticsearch index?

Question

Let say I have a thousand keys, and I would want to store the associated values. The intuitive approach seems to be something like

{
   "key1":"someval",
   "key2":"someotherval",
    ...
}

Is this a bad design pattern for elasticsearch index to have thousands of keys? Would each keys introduced this way create overhead for every documents under the index?

Answer 1

If you know there is an upper limit to the number of keys you'll have, a few thousand fields is not a problem.

The problem is when you have an unbounded set of keys, e.g. when the key is derived from a value, as you'll have a continuously growing mapping and thus also cluster state. It can also lead to quirky searches.

This is a common enough question/issue that I dedicated a section to it in my article on Troubleshooting Elasticsearch searches, for Beginners.

In short, thousands of fields is no problem - not having control of the mapping is.