For frontend developers usually is not very clear how server variables are injected in JSP and what data is presented in this variables. To simplify their work could be used JSTL function, which will output server variable in json format.
I had a task to optimize user creation and storing. Before changes on each anonymous checkout a new user was creates with ID in format RANDOM_UID|USER_EMAILand we had a lot of users who used anonymous checkout more than once. After changes only one user with ID in format USER_EMAIL for all anonymous checkouts was used. As a part of the task I need to migrate all old users to new format users. First version of moigration script had an execution time took more than 3 days for processing around 7 millions of people.
Adding Category itemtype for indexing doesn’t require any specific actions, except adding corresponding changes to solr.impex files. But in case of two different itemtypes in one SolrFacetSearchConfig it is not enough just to change impexes you also need to adopt java source code.