cloud-fan edited a comment on issue #25651: [SPARK-28948][SQL] Support passing all Table metadata in TableProvider URL: https://github.com/apache/spark/pull/25651#issuecomment-544593636 @rdblue , when I try to have separated methods `inferSchema` and `inferPartitioning`, problems keep popping up (mostly from file source v2). The major problems hit so far: 1. `inferSchema`/`inferPartitioning` need to list files, and we should only do file listing once when we scan a directory without user-specified schema. This can be resolved by using a static cache or simply cache the listed files in the `FileDataSourceV2` instance. 2. when writing to a directory, no schema/partition inference should be done. It looks to me that we need to have 2 separated methods `getTableToRead` and `getTableToWrite`, while `getTableToWrite` does not take schema/partitioning and we don't need to call `inferSchema`/`inferPartitioning`. But this makes the API ugly. I feel that, the existing API (`getTable` with several overloads) is more flexible and allows implementations to have its special logic. For example, it allows file source to do schema inference lazily, which won't be triggered at all during write.
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