Speed up display of parent processes

[BartChris]

Fixes #5934

As outlined in issue #5934, we currently face performance problems when working with parent processes in the editor, which contain a lot of children elements. In the issue discussion i thought that the problem lies in opening a lot of XML files for detection of the base type, but we are already using the index. I discovered that the problem seems to stem from accessing the index hundreds of times.
I tried to correct that and was able to bring the time to show a parent process with 600 files from more than 30 seconds to around 3 seconds.
My implementation does four things:

• Instead of retrieving the base types for the linked processes when the structure tree is constructed recursively, i fetch all the base types before the structure tree is constructed
• Instead of retrieving the documents from the Elasticsearch index one by one i fetch them in one go using the Mget operation. (https://www.elastic.co/guide/en/elasticsearch/reference/7.17/docs-multi-get.html)
• We do not have to convert the document to a DTO since we only need the basetype, which we can fetch directly from the Elasticsearch response, which is reduced in size by specifiying the only source field we need: "baseType"
• We can use a view cache for already derived views

[henning-gerhardt]

Changes looks good and there is a big speed improvement.

Two things:

1. I'm only not sure how this change will survive the hibernate-search integration as there is a total other access to this needed data.
2. This change should be back ported to the 3.7.x release branch as it is a big improvement for the 3.7.x releases which may be used a long time and it is currently not possible to change the metadata of hierarchy processes with a lot of child processes.

[solth]

• I'm only not sure how this change will survive the hibernate-search integration as there is a total other access to this needed data.

• This change should be back ported to the 3.7.x release branch as it is a big improvement for the 3.7.x releases which may be used a long time and it is currently not possible to change the metadata of hierarchy processes with a lot of child processes.

I agree with both points. It would be great to get this improvement for Kitodo 3.7 as well. Concerning the integration of hibernate search, perhaps @matthias-ronge could weigh in on estimating wether he thinks the changes of this pull request get in the way of his ongoing works or whether they can be incorporated into hibernate search as well.

[BartChris]

I backported the changes to the 3.7 branch.

I'm only not sure how this change will survive the hibernate-search integration as there is a total other access to this needed data.

This was something i thought about as well. My impression from the Hibernate Branch and the discussion around it is, that we will strive to still enable index-based functionality including custom searches, when this is important for the functionality or it speeds up things significantly.
We will have to use the Hibernate Search abstraction, which unfortunately does not allow for MGET-Operations i suppose. But it should be possible to instead construct a normal search for multiple IDs. And we can also make the search more efficient by only retrieve what we need using projections. (https://docs.jboss.org/hibernate/stable/search/reference/en-US/html_single/#projections)
While I haven't tested it myself, I hope - and expect - that we can still take full advantage of the underlying index, even with the added abstraction layer introduced by Hibernate Search.