spark 2.4.3
spark读取hive表，步骤：
1）hive-site.xml
hive-site.xml放到$SPARK_HOME/conf下
2）enableHiveSupport
3) 测试代码
val sparkConf = new SparkConf().setAppName(getName)
val sc = new SparkContext(sparkConf)
val spark = SparkSession.builder.config(sparkConf).enableHiveSupport().getOrCreate()
spark.sql("show databases").rdd.foreach(println)
使用$SPARK_HOME/bin/spark-submit提交任务后发现并不能读取到hive的数据库，相关日志如下
19/05/31 13:11:31 WARN SparkContext: Using an existing SparkContext; some configuration may not take effect.
19/05/31 13:11:31 INFO SharedState: loading hive config file: file:/export/spark-2.4.3-bin-hadoop2.6/conf/hive-site.xml
19/05/31 13:11:31 INFO SharedState: spark.sql.warehouse.dir is not set, but hive.metastore.warehouse.dir is set. Setting spark.sql.warehouse.dir to the value of hive.metastore.warehouse.dir ('/user/hive/warehouse').
19/05/31 13:11:31 INFO SharedState: Warehouse path is '/user/hive/warehouse'.
19/05/31 13:11:31 INFO StateStoreCoordinatorRef: Registered StateStoreCoordinator endpoin
说明已经读到hive-site.xml；
进一步测试，使用$SPARK_HOME/bin/spark-sql或者$SPARK_HOME/bin/spark-shell发现都可以读到hive数据库，很神奇有没有，
$SPARK_HOME/bin/spark-shell启动的类为org.apache.spark.repl.Main
"${SPARK_HOME}"/bin/spark-submit --class org.apache.spark.repl.Main --name "Spark shell" "$@"跟进org.apache.spark.repl.Main代码
...
val builder = SparkSession.builder.config(conf)
if (conf.get(CATALOG_IMPLEMENTATION.key, "hive").toLowerCase(Locale.ROOT) == "hive") {
if (SparkSession.hiveClassesArePresent) {
// In the case that the property is not set at all, builder's config
// does not have this value set to 'hive' yet. The original default
// behavior is that when there are hive classes, we use hive catalog.
sparkSession = builder.enableHiveSupport().getOrCreate()
logInfo("Created Spark session with Hive support")
} else {
// Need to change it back to 'in-memory' if no hive classes are found
// in the case that the property is set to hive in spark-defaults.conf
builder.config(CATALOG_IMPLEMENTATION.key, "in-memory")
sparkSession = builder.getOrCreate()
logInfo("Created Spark session")
}
} else {
// In the case that the property is set but not to 'hive', the internal
// default is 'in-memory'. So the sparkSession will use in-memory catalog.
sparkSession = builder.getOrCreate()
logInfo("Created Spark session")
}
sparkContext = sparkSession.sparkContext
sparkSession
...
发现和测试代码有些差异，关键是在倒数第二行，这里是先创建SparkSession，再从SparkSession中获取SparkContext，另外注意到之前有个WARN级别的日志
修改测试代码
val sparkConf = new SparkConf().setAppName(getName)
//val sc = new SparkContext(sparkConf)
val spark = SparkSession.builder.config(sparkConf).enableHiveSupport().getOrCreate()
val sc = spark.sparkContext
spark.sql("show databases").rdd.foreach(println)
这次果然ok了，详细原因有空再看，未完待续；