Github user gatorsmile commented on a diff in the pull request: https://github.com/apache/spark/pull/16685#discussion_r97619926 --- 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 -- Well, since Spark 2.1, we already provide the parm for limiting the max num of concurrent JDBC connection when inserting data to JDBC tables. The parm is `numPartitions`.
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