Fixes #39298 - Use bulk insert for new fact values on persisted hosts

[pablomh]

Summary

Replace per-fact create! loop with a single insert_all for new facts on persisted hosts, reducing DB round-trips by ~94% (108 INSERTs → 6).

Changes

• fact_importer.rb: add_new_facts partitions into compose facts (nil values, handled individually) and regular facts (bulk inserted via insert_all)
• bulk_insert_new_fact_values: new method using FactValue.insert_all with unique_by: [:fact_name_id, :host_id]
• Counter initialization: @counters = { added: 0, updated: 0, deleted: 0 } prevents nil access

How to test

1. bundle exec rake test TEST=test/unit/fact_importer_test.rb
2. Register a host and verify facts are imported correctly

[ekohl]

#8823 was the last attempt at improving fact import performance. Have you had a look at that? The benchmark code may also be useful as a reference.

[ekohl]

I'm surprised this doesn't use the parent:

def initialize(host, facts = {})
      # Try to assign these facts to the correct host as per the facts say
      # If that host isn't created yet, the host parameter will contain it
      host = Host.find_by(:name => facts[:ansible_facts][:ansible_fqdn] ||
                                    facts[:ansible_facts][:fqdn]) ||
              host
    super(host, facts[:ansible_facts])
end

[pablomh]

Agreed — the duplicated initialization is pre-existing tech debt. Refactoring it to use super would change the host resolution and fact extraction logic, so we kept it out of scope for this PR.

[pablomh]

The key difference is which method each PR targets: #8823 applied upsert_all to update_facts (existing facts changing value), where the current code already uses update_all with no callbacks — so there was no measurable gain. Our PR applies insert_all to add_new_facts (facts being created for the first time), where the current code calls create! per fact with individual INSERTs.

During registration this is the dominant path — all facts are new (100 per RHEL 8 host, 117 per RHEL 9/10 host) — and at concurrent scale the per-fact INSERTs compound. Measured on a 16-CPU Satellite with only this patch applied (no other changes), mixed workload (50% RHEL 8, 25% RHEL 9, 25% RHEL 10):

Concurrency	INSERTs/host (before → after)	AR P50 (before → after)	AR P95 (before → after)
152	100 (el8) / 117 (el9,el10) → 1	2,610ms → 1,297ms (−50%)	8,214ms → 3,350ms (−59%)
304	100 (el8) / 117 (el9,el10) → 1	4,579ms → 2,004ms (−56%)	11,922ms → 6,232ms (−48%)
456	100 (el8) / 117 (el9,el10) → 1	8,492ms → 2,619ms (−69%)	13,036ms → 6,884ms (−47%)
608	100 (el8) / 117 (el9,el10) → 1	8,701ms → 3,215ms (−63%)	13,963ms → 7,566ms (−46%)
760	100 (el8) / 117 (el9,el10) → 1	9,789ms → 3,666ms (−63%)	14,138ms → 7,120ms (−50%)