Speed up Snowflake column comments, while still avoiding errors (#3543)

* Have our cake and eat it quickly, too * Update changelog
dbt-labs · Jul 7, 2021 · 85627aa · 85627aa
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diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -22,6 +22,10 @@ Contributors:
 
 ## dbt 0.20.0 (Release TBD)
 
+### Fixes
+
+- Avoid slowdown in column-level `persist_docs` on Snowflake, while preserving the error-avoidance from [#3149](https:/fishtown-analytics/dbt/issues/3149) ([#3541](https:/fishtown-analytics/dbt/issues/3541), [#3543](https:/fishtown-analytics/dbt/pull/3543))
+
 ## dbt 0.20.0rc2 (June 30, 2021)
 
 ### Fixes

diff --git a/plugins/snowflake/dbt/include/snowflake/macros/adapters.sql b/plugins/snowflake/dbt/include/snowflake/macros/adapters.sql
@@ -155,8 +155,10 @@
 
 
 {% macro snowflake__alter_column_comment(relation, column_dict) -%}
- {% for column_name in column_dict %}
- comment if exists on column {{ relation }}.{{ adapter.quote(column_name) if column_dict[column_name]['quote'] else column_name }} is $${{ column_dict[column_name]['description'] | replace('$', '[$]') }}$$;
+ {% set existing_columns = adapter.get_columns_in_relation(relation) | map(attribute="name") | list %}
+ alter {{ relation.type }} {{ relation }} alter
+ {% for column_name in column_dict if (column_name in existing_columns) or (column_name|upper in existing_columns) %}
+ {{ adapter.quote(column_name) if column_dict[column_name]['quote'] else column_name }} COMMENT $${{ column_dict[column_name]['description'] | replace('$', '[$]') }}$$ {{ ',' if not loop.last else ';' }}
  {% endfor %}
 {% endmacro %}