Fix dbt clone for Snowflake Iceberg tables by jecolvin · Pull Request #1768 · dbt-labs/dbt-adapters

jecolvin · 2026-03-17T14:10:01Z

Summary

Detect Iceberg source tables in the clone macro via load_cached_relation and emit CREATE OR REPLACE ICEBERG TABLE ... CLONE ... instead of CREATE OR REPLACE [TRANSIENT] TABLE ... CLONE ...
Omit the transient keyword for Iceberg clones (Iceberg tables cannot be transient)
Add functional test for cloning an Iceberg table

Resolves #1767

Test plan

Existing clone tests pass (TestSnowflakeClonePossible, TestSnowflakeCloneTrainsentTable)
New TestSnowflakeCloneIcebergTable test passes against a Snowflake account with an Iceberg-enabled external volume
Verify generated SQL with --log-level debug shows CREATE OR REPLACE ICEBERG TABLE for Iceberg sources and CREATE OR REPLACE TRANSIENT TABLE for regular sources

Copilot

Pull request overview

Updates the Snowflake adapter’s clone materialization to correctly clone Iceberg source tables by generating Iceberg-specific DDL, and adds a functional test to validate the behavior.

Changes:

Detect Iceberg source relations during dbt clone and emit CREATE OR REPLACE ICEBERG TABLE ... CLONE ... when appropriate.
Ensure transient is not emitted for Iceberg clones (since Iceberg tables cannot be transient).
Add a functional test that clones an Iceberg table and asserts the cloned relation is also Iceberg.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
dbt-snowflake/src/dbt/include/snowflake/macros/materializations/clone.sql	Conditionally renders Iceberg vs transient table clone DDL based on cached source relation metadata.
dbt-snowflake/tests/functional/adapter/dbt_clone/test_dbt_clone.py	Adds a functional test case covering cloning an Iceberg table and validating the cloned relation type.
dbt-snowflake/.changes/unreleased/Fixes-20260317-100403.yaml	Adds a changelog entry documenting the Iceberg clone fix.

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dbt-snowflake/tests/functional/adapter/dbt_clone/test_dbt_clone.py

jecolvin · 2026-03-24T13:23:20Z

@colin-rogers-dbt Pushed a fix for the failing integration test!

Copilot

Pull request overview

Updates Snowflake’s dbt clone behavior to support cloning from Iceberg source tables by generating Iceberg-specific DDL and adding a functional regression test.

Changes:

Detect Iceberg source tables during clone and emit CREATE OR REPLACE ICEBERG TABLE ... CLONE ... when appropriate.
Omit transient for Iceberg clones (since Iceberg tables cannot be transient).
Add a functional test validating that an Iceberg table can be cloned and remains Iceberg-format.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
`dbt-snowflake/src/dbt/include/snowflake/macros/materializations/clone.sql`	Adds Iceberg detection and conditional DDL generation for clone operations.
`dbt-snowflake/tests/functional/adapter/dbt_clone/test_dbt_clone.py`	Adds a functional test for cloning an Iceberg table and verifying the cloned relation format.
`dbt-snowflake/.changes/unreleased/Fixes-20260317-100403.yaml`	Adds an unreleased changelog entry documenting the fix.

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dbt-snowflake/src/dbt/include/snowflake/macros/materializations/clone.sql

dbt-snowflake/tests/functional/adapter/dbt_clone/test_dbt_clone.py

jecolvin · 2026-04-01T18:10:24Z

@colin-rogers-dbt I've addressed the latest round of feedback!

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

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Copilot · 2026-04-01T20:44:30Z

dbt-snowflake/src/dbt/include/snowflake/macros/materializations/clone.sql

+    {#- Cache miss: query Snowflake directly -#}
+    {%- set show_sql -%}
+        show tables like '{{ relation.identifier }}' in schema {{ relation.database }}.{{ relation.schema }}
+    {%- endset -%}
+    {%- set results = run_query(show_sql) -%}
+    {%- for row in results -%}
+        {%- if row['name'] == relation.identifier -%}
+            {{ return(row['is_iceberg'] in ('Y', 'YES')) }}
+        {%- endif -%}
+    {%- endfor -%}


The cache-miss fallback builds SHOW TABLES SQL using raw relation.database/relation.schema and compares row['name'] to relation.identifier case-sensitively. This will mis-detect Iceberg tables when quoting policies or case-sensitive identifiers are used (Snowflake often returns name uppercased), which can cause the clone macro to emit the wrong DDL and fail. Prefer using adapter.get_relation(database=..., schema=..., identifier=...) (or relation.include(identifier=False) / IN SCHEMA IDENTIFIER(...)) and compare names case-insensitively; also escape quotes in the LIKE literal.

Suggested change

{#- Cache miss: query Snowflake directly -#}

{%- set show_sql -%}

show tables like '{{ relation.identifier }}' in schema {{ relation.database }}.{{ relation.schema }}

{%- endset -%}

{%- set results = run_query(show_sql) -%}

{%- for row in results -%}

{%- if row['name'] == relation.identifier -%}

{{ return(row['is_iceberg'] in ('Y', 'YES')) }}

{%- endif -%}

{%- endfor -%}

{#- Cache miss: query Snowflake directly via adapter.get_relation -#}

{%- set source_relation = adapter.get_relation(

database=relation.database,

schema=relation.schema,

identifier=relation.identifier

) -%}

{%- if source_relation is not none -%}

{{ return(source_relation.is_iceberg_format) }}

{%- endif -%}

Copilot · 2026-04-01T20:44:31Z

dbt-snowflake/tests/functional/adapter/dbt_clone/test_dbt_clone.py

+    state_path = os.path.join(project_root, "state")
+    if not os.path.exists(state_path):
+        os.makedirs(state_path)
+    shutil.copyfile(f"{project_root}/target/manifest.json", f"{project_root}/state/manifest.json")


copy_state builds paths with hardcoded "{project_root}/..." instead of os.path.join(...). This can break on Windows path separators and is inconsistent with the surrounding os.path.join usage; consider using os.path.join(project_root, "target", "manifest.json") / os.path.join(project_root, "state", "manifest.json").

Suggested change

shutil.copyfile(f"{project_root}/target/manifest.json", f"{project_root}/state/manifest.json")

src_manifest = os.path.join(project_root, "target", "manifest.json")

dst_manifest = os.path.join(project_root, "state", "manifest.json")

shutil.copyfile(src_manifest, dst_manifest)

Copilot · 2026-04-01T20:44:31Z

dbt-snowflake/.changes/unreleased/Fixes-20260317-100403.yaml

+    Author: jcolvin
+    Issue: "1767"


The custom: block indentation is inconsistent with other .changes/unreleased/*.yaml entries in this repo (e.g., .changes/unreleased/Fixes-20260306-163035.yaml:4-6 uses two-space indentation). Align the indentation to match the established format to keep changelog tooling and diffs consistent.

Suggested change

Author: jcolvin

Issue: "1767"

Author: jcolvin

Issue: "1767"

colin-rogers-dbt · 2026-04-01T22:10:12Z

dbt-snowflake/src/dbt/include/snowflake/macros/materializations/clone.sql

+        {{ return(source_relation.is_iceberg_format) }}
+    {%- endif -%}
+
+    {#- Cache miss: query Snowflake directly -#}


I don't think we'll need this as the cache should already have the relation but if we do need this then we should be able to use adapter.get_relation instead of a custom show command

The clone macro now detects whether the source relation is an Iceberg table via load_cached_relation and emits CREATE ICEBERG TABLE ... CLONE instead of CREATE TABLE ... CLONE. The transient keyword is correctly omitted for Iceberg clones since Iceberg tables cannot be transient. Resolves dbt-labs#1767

load_cached_relation returns None during cross-schema clone operations because the source schema is not in the adapter cache. Fall back to querying Snowflake directly via SHOW TABLES to detect iceberg format. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Harden SHOW TABLES fallback: add IN SCHEMA keyword and filter by exact name match to avoid LIKE wildcard false positives - Use SNOWFLAKE_TEST_ICEBERG_EXTERNAL_VOLUME env var for test portability - Extract copy_state/run_and_save_state to shared module-level functions Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Remove SHOW TABLES fallback in snowflake__is_iceberg_table per reviewer feedback — cache should already have the relation - Use os.path.join consistently in copy_state helper Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

jecolvin requested a review from a team as a code owner March 17, 2026 14:10

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Fix dbt clone for Snowflake Iceberg tables#1768

Fix dbt clone for Snowflake Iceberg tables#1768
jecolvin wants to merge 4 commits intodbt-labs:mainfrom
jecolvin:fix/snowflake-clone-iceberg-tables

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-    shutil.copyfile(f"{project_root}/target/manifest.json", f"{project_root}/state/manifest.json")
+    src_manifest = os.path.join(project_root, "target", "manifest.json")
+    dst_manifest = os.path.join(project_root, "state", "manifest.json")
+    shutil.copyfile(src_manifest, dst_manifest)

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