Utilise struct stats when available #656
Conversation
Co-authored-by: Will Jones <willjones127@gmail.com>
…struct_stats_when_available
python/tests/test_table_read.py
Outdated
| @@ -193,16 +193,6 @@ def test_read_table_with_stats(): | |||
| # assert data.num_rows == 0 | |||
|
|
|||
|
|
|||
| def test_read_table_with_only_struct_stats(): | |||
There was a problem hiding this comment.
I'm removing this because everything should now be covered by the lower level rust test I added. This did surface something interesting though. It seems like the DeltaTable.to_pyarrow_schema() function cannot handle the struct of array of map type I put in my test data. I think this is probably an issue for another time though.
| Field::Decimal(decimal) => match BigInt::from_signed_bytes_be(decimal.data()).to_f64() { | ||
| Some(int) => json!(int / (10_i64.pow((decimal.scale()).try_into().unwrap()) as f64)), | ||
| _ => serde_json::Value::Null, | ||
| }, |
There was a problem hiding this comment.
So on the decimal representation, it does seem to be the case that the Spark implementation writes them out as numbers in the JSON file. I can't find the implementation code, but it does seem like they have a special parser that handles decimals. We don't so I'm worried about having a lossy conversion of Decimal into float.
It's a complicated subject and sort of an edge case, so I'm fine with this for now, but we should do a follow-up to make sure we are using decimal statistics appropriately.
There was a problem hiding this comment.
Yeah I was a bit concerned about this too. I'm tempted to just remove it since that is probably a safer option.
Co-authored-by: Will Jones <willjones127@gmail.com>
Co-authored-by: Will Jones <willjones127@gmail.com>
Co-authored-by: Will Jones <willjones127@gmail.com>
Co-authored-by: Will Jones <willjones127@gmail.com>
Co-authored-by: Will Jones <willjones127@gmail.com>
|
Thanks @Tom-Newton ! |
|
I'm afraid I made a mistake in this PR. I just realised while testing #712. I've a made a follow up PR to fix this. |
# Description When a delta table's schema is evolved the struct stat schemas in checkpoints are also evolved. Since the struct stats are stored in a columnar way adding a single file with the new columns will cause nulls to appear in the struct stats for all other files. This is a significant difference compared to the json stats. Unfortunately I overlooked this in #656 for both nullCounts and min/max values. This caused parsed struct stats to have extra columns full of nulls. I don't know if this was actually an issue at all but it should be fixed even if just for the sake of the warnings spam. ``` [2022-10-24T22:13:22Z WARN deltalake::action::parquet_read] Expect type of nullCount field to be struct or int64, got: null [2022-10-24T22:13:22Z WARN deltalake::action::parquet_read] Expect type of nullCount field to be struct or int64, got: null [2022-10-24T22:13:22Z WARN deltalake::action::parquet_read] Expect type of nullCount field to be struct or int64, got: null [2022-10-24T22:13:22Z WARN deltalake::action::parquet_read] Expect type of nullCount field to be struct or int64, got: null [2022-10-24T22:13:22Z WARN deltalake::action::parquet_read] Expect type of nullCount field to be struct or int64, got: null ``` # Related Issue(s) - Relates to #653 but for the most part its an already solved issue. # Changes: - Replace the test data with similar test data that includes a schema evolution. - Add error handling for min/max values to ensure warnings will be logged for other unexpected types (there probably shouldn't be any). As a total rust noob I originally filled with nulls but I think that was a mistake. - Ignore nulls for min/max stats and null count stats since these are expected after schema evolution and should be ignored without logging a warning. Usual disclaimer on a PR from me: I don't know what I'm doing writing rust code. (thanks to wjones for tidying up my dodgy rust code 🙂) Co-authored-by: Will Jones <willjones127@gmail.com>
Description
Updates
Add.get_stats()to use parquet structs stats when available by parsing them to the same format json stats are parsed to. This means delta-rs can still utilise stats on tables where checkpoint files are configured to only store struct stats.Related Issue(s)
Documentation
I did my best but I've never written rust code before...