Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/15998#discussion_r89411482
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/ExternalCatalog.scala
---
@@ -189,6 +189,38 @@ abstract class ExternalCatalog {
spec: TablePartitionSpec): Option[CatalogTablePartition]
/**
+ * List the names of all partitions that belong to the specified table,
assuming it exists.
+ *
+ * A partial partition spec may optionally be provided to filter the
partitions returned.
+ * For instance, if there exist partitions (a='1', b='2'), (a='1',
b='3') and (a='2', b='4'),
+ * then a partial spec of (a='1') will return the first two only.
+ *
+ * We provide a default implementation here which simply delegates to
the `listPartitions`
+ * method. For efficiency's sake, overriding this method is recommended
for external catalogs
+ * that can list partition names directly.
+ * @param db database name
+ * @param table table name
+ * @param partialSpec partition spec
+ */
+ def listPartitionNames(
+ db: String,
+ table: String,
+ partialSpec: Option[TablePartitionSpec] = None): Seq[String] = {
--- End diff --
My worry is that when we create a new implementation of the external
catalog, we'd forget to implement this, leading to bad performance.
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