perf: honor incremental_apply_config_changes flag in V1 incremental path

The V1 incremental merge path called adapter.get_relation_config() unconditionally,
forcing metadata fetches (tags, column_tags, constraints, column_masks, tblproperties,
describe_extended) on every incremental run even when the user opted out via
incremental_apply_config_changes=false. The V2 path already honors the flag via the
process_config_changes() macro; V1 ignored it.

Wrap the V1 get_relation_config call in a flag check matching the V2 semantics. When
the flag is false, _configuration_changes stays None and the existing apply-block
guard (`if _configuration_changes is not none`) short-circuits the apply, so no
metadata is fetched or applied. Default behavior (flag=true) is unchanged.

Co-authored-by: Isaac

Author: moomindani

CHANGELOG.md

@@ -1,3 +1,9 @@
+## dbt-databricks 1.13.0 (TBD)
+
+### Under the Hood
+
+- Honor `incremental_apply_config_changes` in the V1 incremental merge path, allowing users to skip metadata diff queries (tags, column_tags, constraints, column_masks, tblproperties, describe_extended) when set to `false`. Matches the existing V2 behavior. ([#1402](https://github.com/databricks/dbt-databricks/issues/1402))
+
 ## dbt-databricks 1.12.1 (June 10, 2026)
 
 ### Features

dbt/include/databricks/macros/materializations/incremental/incremental.sql

@@ -133,9 +133,12 @@
         {{ set_overwrite_mode('DYNAMIC') }}
       {%- endif -%}
       {#-- Relation must be merged --#}
-      {%- set model_config = adapter.get_config_from_model(config.model) -%}
-      {%- set _existing_config = adapter.get_relation_config(existing_relation, model_config) -%}
-      {%- set _configuration_changes = model_config.get_changeset(_existing_config) -%}
+      {%- set _configuration_changes = none -%}
+      {%- if config.get('incremental_apply_config_changes', True) | as_bool -%}
+        {%- set model_config = adapter.get_config_from_model(config.model) -%}
+        {%- set _existing_config = adapter.get_relation_config(existing_relation, model_config) -%}
+        {%- set _configuration_changes = model_config.get_changeset(_existing_config) -%}
+      {%- endif -%}
       {%- call statement('create_temp_relation', language=language) -%}
         {{ create_table_as(True, temp_relation, compiled_code, language) }}
       {%- endcall -%}

tests/functional/adapter/incremental/fixtures.py

@@ -85,6 +85,16 @@
 select cast(1 as bigint) as id
 """
 
+metadata_fetch_incremental_skip_config_changes_sql = """
+{{ config(
+    materialized = 'incremental',
+    unique_key = 'id',
+    incremental_apply_config_changes = false,
+) }}
+
+select cast(1 as bigint) as id
+"""
+
 metadata_fetch_no_tags_schema = """
 version: 2
 

tests/functional/adapter/incremental/test_v1_incremental_apply_config_changes.py

@@ -0,0 +1,36 @@
+import pytest
+from dbt.tests import util
+
+from tests.functional.adapter.fixtures import (
+    MaterializationV1Mixin,
+    fail_if_tag_and_column_tag_fetch_called_macros,
+)
+from tests.functional.adapter.incremental import fixtures
+
+
+@pytest.mark.skip_profile("databricks_cluster")
+class TestV1IncrementalApplyConfigChangesFalseSkipsTagFetch(MaterializationV1Mixin):
+    """When `incremental_apply_config_changes` is false, the V1 incremental merge path
+    must skip the get_relation_config metadata fetches even if the model declares tags.
+    """
+
+    @pytest.fixture(scope="class")
+    def models(self):
+        return {
+            "metadata_fetch_incremental.sql": (
+                fixtures.metadata_fetch_incremental_skip_config_changes_sql
+            ),
+            "schema.yml": fixtures.metadata_fetch_table_tags_schema,
+        }
+
+    @pytest.fixture(scope="class")
+    def macros(self):
+        return {"fail_if_tag_fetch_called.sql": fail_if_tag_and_column_tag_fetch_called_macros}
+
+    def test_v1_incremental_skips_metadata_fetch_when_flag_false(self, project):
+        # First run creates the table; second run exercises the existing-relation merge path
+        # where get_relation_config would normally fire metadata queries.
+        # Tags are declared on the model, so without the flag the run would call fetch_tags
+        # and fail. The flag must bypass the entire get_relation_config call.
+        util.run_dbt(["run"])
+        util.run_dbt(["run"])