Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/16685#discussion_r97622295
--- Diff:
sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala
---
@@ -722,14 +724,246 @@ object JdbcUtils extends Logging {
}
/**
+ * Check whether a table exists in a given database
+ *
+ * @return True if the table exists.
+ */
+ @transient
+ def checkTableExists(targetDb: String, tableName: String): Boolean = {
+ val dbc: Connection = DriverManager.getConnection(targetDb)
+ val dbm = dbc.getMetaData()
+ // Check if the table exists. If it exists, perform an upsert.
+ // Otherwise, do a simple dataframe write to the DB
+ val tables = dbm.getTables(null, null, tableName, null)
+ val exists = tables.next() // Returns false if next does not exist
+ dbc.close()
+ exists
+ }
+
+ // Provide a reasonable starting batch size for database operations.
+ private val DEFAULT_BATCH_SIZE: Int = 200
+
+ // Limit the number of database connections. Some DBs suffer when there
are many open
+ // connections.
+ private val DEFAULT_MAX_CONNECTIONS: Int = 50
--- End diff --
Please see the logics
[here](https://github.com/ilganeli/spark/blob/56545ed88f665ed57a50a8c5d114c6ae8130eab3/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala#L714-L720).
We already can do it for Insert by using `coalesce`.
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