[I] fs.comet.libhdfs.schemes is matched after the s3a alias rewrite, so listing s3 also routes s3a through libhdfs [datafusion-comet]

["andygrove (via GitHub)" <gi...@apache.org>]

andygrove opened a new issue, #5816:
URL: https://github.com/apache/datafusion-comet/issues/5816

   ## Describe the bug
   
   `fs.comet.libhdfs.schemes` is compared against the scheme *after* the s3-alias rewrite, so listing `s3` also routes `s3a://` reads through libhdfs. Before #5314 the two were independent: the libhdfs decision was taken from the URL the user typed, and `s3a` was normalized to `s3` only when it was not libhdfs-routed.
   
   `prepare_object_store_with_configs` in `native/core/src/parquet/parquet_support.rs` now reads:
   
   ```rust
   let url = normalize_object_store_url(url.as_str(), object_store_configs)?;
   let is_hdfs_scheme = is_hdfs_scheme(&url, object_store_configs);
   ```
   
   `normalize_object_store_url` guards its own early return with `is_hdfs_scheme`, so an `s3a://` URL whose scheme is not in the list falls through to `rewrite_alias_to_s3` and comes back as `s3://`. The classification on the next line then sees `s3`, matches the list, and selects the Hadoop backend.
   
   Before #5314 the order was the other way round:
   
   ```rust
   let is_hdfs_scheme = is_hdfs_scheme(&url, object_store_configs);
   let mut scheme = url.scheme();
   if !is_hdfs_scheme && scheme == "s3a" { scheme = "s3"; url.set_scheme("s3")?; }
   ```
   
   ## Steps to reproduce
   
   With `fs.comet.libhdfs.schemes=s3` set and no `s3a` entry, read `s3a://bucket/file.parquet`. The scan is served by `create_hdfs_object_store` instead of the native S3 store.
   
   Adding this to `native/core/src/parquet/objectstore/s3_blob_fs_support.rs` on `424c31aa7` fails:
   
   ```rust
   #[test]
   fn s3a_is_not_libhdfs_routed_when_only_s3_is_listed() {
       let configs = HashMap::from([(
           "fs.comet.libhdfs.schemes".to_string(),
           "s3".to_string(),
       )]);
       let typed = Url::parse("s3a://bucket/f.parquet").unwrap();
       assert!(!is_hdfs_scheme(&typed, &configs));
       let normalized = normalize_object_store_url("s3a://bucket/f.parquet", &configs).unwrap();
       assert!(!is_hdfs_scheme(&normalized, &configs));
   }
   ```
   
   Output:
   
   ```
   PROBE typed scheme      = s3a
   PROBE typed  is_hdfs    = false
   PROBE normalized scheme = s3
   PROBE final  is_hdfs    = true
   ```
   
   The converse case is fine: with `fs.comet.libhdfs.schemes=s3a`, `normalize_object_store_url` returns early and the scheme keeps its spelling, so `s3a` stays libhdfs-routed as asked.
   
   ## Expected behavior
   
   The libhdfs decision should be taken once, from the scheme the user wrote, and carried through the alias rewrite rather than being recomputed from the rewritten URL.
   
   ## Additional context
   
   Found while reviewing #5503, whose `isolates_backends_even_when_s3_alias_and_configs_match` test covers exactly this pair (`s3a` native versus `s3` libhdfs under one config) and fails in CI on the merge with `main` while passing on the branch alone. That test is a good regression guard for this fix.
   
   Introduced by #5314. cc @comphead @sunchao
   


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Re: [I] fs.comet.libhdfs.schemes is matched after the s3a alias rewrite, so listing s3 also routes s3a through libhdfs [datafusion-comet]

["comphead (via GitHub)" <gi...@apache.org>]

comphead commented on issue #5816:
URL: https://github.com/apache/datafusion-comet/issues/5816#issuecomment-5607751369

   Thanks @andygrove I'm on it


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Re: [I] fs.comet.libhdfs.schemes is matched after the s3a alias rewrite, so listing s3 also routes s3a through libhdfs [datafusion-comet]

["comphead (via GitHub)" <gi...@apache.org>]

comphead closed issue #5816: fs.comet.libhdfs.schemes is matched after the s3a alias rewrite, so listing s3 also routes s3a through libhdfs
URL: https://github.com/apache/datafusion-comet/issues/5816


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