The queries to update the number of biblios and the number of items for any given import batch are much slower than they need to be. UPDATE import_batches SET num_biblios = (SELECT COUNT(*) FROM import_records WHERE import_batch_id = import_batches.import_batch_id AND record_type = 'biblio') WHERE import_batch_id = ? UPDATE import_batches SET num_items = (SELECT COUNT(*) FROM import_records JOIN import_items USING (import_record_id) WHERE import_batch_id = import_batches.import_batch_id AND record_type = 'biblio') WHERE import_batch_id = ?") The "AND record_type = 'biblio'" lines are unnecesary; every record within the same import_batch_id will have the same record_type, and more importantly, 'biblio' is currently the only supported type. Removing the line changes the return time of the subquery from over 2 seconds down to 0.01 seconds (on my machine with 34944 items in a batch). I think this is going to be faster than adding an index on record_type.
bug affected to Koha 3.6. Entries must be attached to rel_3_8 only when the patch is pushed here (and if it's an ENH)
I will try implementing an index and checking the speed, on the off chance we do get batch import of authorities working in the future
As we have authority batch import in current versions, I think the proposed improvement is invalid now.