Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Update RTRIM scalar function to support Utf8View #11916

Closed
tshauck opened this issue Aug 9, 2024 · 2 comments · Fixed by #11948
Closed

Update RTRIM scalar function to support Utf8View #11916

tshauck opened this issue Aug 9, 2024 · 2 comments · Fixed by #11948
Assignees
Labels
enhancement New feature or request

Comments

@tshauck
Copy link
Contributor

tshauck commented Aug 9, 2024

Part of #11752 and #11790

Currently, a call to RTRIM with a Utf8View datatypes induces a cast. After the change that fixes this issue, it should not.

query TT
EXPLAIN SELECT
  RTRIM(column1_utf8view) as c1,
  RTRIM(column1_utf8view, 'foo') as c2
FROM test;
----
logical_plan
01)Projection: rtrim(__common_expr_1) AS c1, rtrim(__common_expr_1, Utf8("foo")) AS c2
02)--Projection: CAST(test.column1_utf8view AS Utf8) AS __common_expr_1
03)----TableScan: test projection=[column1_utf8view]

rtrim is defined here: https://github.com/apache/datafusion/blob/e088945c38b74bb1d86dcbb88a69dfc21d59e375/datafusion/functions/src/string/rtrim.rs

casting tests are in: https://github.com/apache/datafusion/blob/main/datafusion/sqllogictest/test_files/string_view.slt

Is your feature request related to a problem or challenge?

We are working to add complete StringView support in DataFusion, which permits potentially much faster processing of string data. See #10918 for more background.

Today, most DataFusion string functions support DataType::Utf8 and DataType::LargeUtf8 and when called with a StringView argument DataFusion will cast the argument back to DataType::Utf8 which is expensive.

To realize the full speed of StringView, we need to ensure that all string functions support the DataType::Utf8View directly.

Describe the solution you'd like

Update the function to support DataType::Utf8View directly

Describe alternatives you've considered

The typical steps are:

  1. Write some tests showing the function doesn't support Utf8View (see the tests in string_view.slt to ensure the arguments are not being cast
  2. Change the Signature of the function to accept Utf8View in addition to Utf8/LargeUtf8
  3. Update the implementation of the function to operate on Utf8View

Example PRs

Additional context

The documentation of string functions can be found here: https://datafusion.apache.org/user-guide/sql/scalar_functions.html#string-functions

To test a function with StringView with datafusion-cli you can use an example like this (replacing starts_with with the relevant function)

> create table foo as values (arrow_cast('foo', 'Utf8View'), arrow_cast('bar', 'Utf8View'));
0 row(s) fetched.
Elapsed 0.043 seconds.

> select starts_with(column1, column2) from foo;
+--------------------------------------+
| starts_with(foo.column1,foo.column2) |
+--------------------------------------+
| false                                |
+--------------------------------------+
1 row(s) fetched.
Elapsed 0.015 seconds.

To see if it is using utf8 view, use EXPLAIN to see the plan and verify there is no CAST. In this example the CAST(column1@0 AS Utf8) indicates that the function is not using Utf8View natively

> explain select starts_with(column1, column2) from foo;
+---------------+------------------------------------------------------------------------------------------------------------------------------+
| plan_type     | plan                                                                                                                         |
+---------------+------------------------------------------------------------------------------------------------------------------------------+
| logical_plan  | Projection: starts_with(CAST(foo.column1 AS Utf8), CAST(foo.column2 AS Utf8))                                                |
|               |   TableScan: foo projection=[column1, column2]                                                                               |
| physical_plan | ProjectionExec: expr=[starts_with(CAST(column1@0 AS Utf8), CAST(column2@1 AS Utf8)) as starts_with(foo.column1,foo.column2)] |
|               |   MemoryExec: partitions=1, partition_sizes=[1]                                                                              |
|               |                                                                                                                              |
+---------------+------------------------------------------------------------------------------------------------------------------------------+
2 row(s) fetched.
Elapsed 0.006 seconds.

It is also often good to test with a constant as well (likewise there should be no cast):

> explain select starts_with(column1, 'foo') from foo;
+---------------+----------------------------------------------------------------------------------------------------------+
| plan_type     | plan                                                                                                     |
+---------------+----------------------------------------------------------------------------------------------------------+
| logical_plan  | Projection: starts_with(CAST(foo.column1 AS Utf8), Utf8("foo"))                                          |
|               |   TableScan: foo projection=[column1]                                                                    |
| physical_plan | ProjectionExec: expr=[starts_with(CAST(column1@0 AS Utf8), foo) as starts_with(foo.column1,Utf8("foo"))] |
|               |   MemoryExec: partitions=1, partition_sizes=[1]                                                          |
|               |                                                                                                          |
+---------------+----------------------------------------------------------------------------------------------------------+
2 row(s) fetched.
Elapsed 0.002 seconds.

### Additional context

_No response_
@Kev1n8
Copy link
Contributor

Kev1n8 commented Aug 10, 2024

take

@alamb
Copy link
Contributor

alamb commented Aug 12, 2024

After #11920 from @Kev1n8 I think this one will be quick to implement

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
enhancement New feature or request
Projects
None yet
Development

Successfully merging a pull request may close this issue.

3 participants