rdblue commented on issue #26150: [SPARK-29501][SQL] SupportsPushDownRequiredColumns should report pruned schema immediately URL: https://github.com/apache/spark/pull/26150#issuecomment-544693234 > In fact Spark always do column pruning at the end, so this can be determined then pushRequiredColumns is called. One of the main reasons for the recent refactor that introduced the scan builder was that ["scan execution order is not obvious"](https://docs.google.com/document/d/1DDXCTCrup4bKWByTalkXWgavcPdvur8a4eEu8x1BzPM/edit#heading=h.s9owpjn3wl3d). The builder was introduced so that the order was clear: filters and projections are pushed, then the read schema is fetched. What you're suggesting, to get the read schema before building the scan, reintroduces the problem this was intended to fix by breaking the guarantee that the read schema is fetched after both projection and filters are pushed. I'm -1 for this change. Also, why can't the v1 fallback path can't build a scan, even if it isn't used?
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