wip/experimental(elasticsearch): Use secondary index for Item and ImageObject

[andersju]

So as to not burden the main ES index with a massive amount of Item and ImageObject records (that we usually don't care much about when searching) we've talked about using separate indices. Here's a very simple way of doing that. Not saying it's necessarily a good way, but just to open up the discussion and get more ideas. It Seems To Work (tm).

Essentially this just splits ES into a "main" index and a "secondary" index, for lack of a better name, with the latter having only Item and ImageObject records. Both are used by default when searching, so no change from the outside. _searchMainOnly=true can be added to not search the secondary index. Index to use when adding/updating records is determined based on type.

To try it locally see https://github.com/libris/devops/tree/feature/use-secondary-es-index for some quick and dirty devops support.

[kwahlin]

Nice! If it seems to work let's try it out in a test environment.

[olovy]

Nice!

Agree that this is a good starting point for measuring potential performance improvements etc.
Also nice to see that splitting the index requires relatively minor changes.
If we are happy with this there is a clear path to generalize it to separate indices per selected base type. And of course select indices to search based on the query.