When trying to query druid tables with uppercase names, the query fails with the error: Table 'TABLE_NAME' does not exist. A similar issue was observed in MySql connector and the attribute option "case-insensitive-name-matching" was added for MySql connector catalogue file. I have tried using the same attribute for Druid catalogue and it doesn't seem to be working.
My guess is you're using Facebook's version of Presto.
TL;DR
You need to use Trino Druid Connector to have support for case-insensitive-name-matching. Trino is formerly known as Presto SQL.
long version
case-insensitive-name-matching was added first in Presto SQL (i am the author of this code, BTW) and later backported to Facebook's Presto, but apparently does not apply to their Druid connector. Trino Druid Connector (fka Presto SQL's Druid Connector) does not have this limitation. You can use either Presto 350 (before project rename) or Trino 351 (after rename).
Related
I am reading Spark Definitive Guide
In the "Spark’s Relationship to Hive" section ..the below lines are give
"With Spark SQL, you can connect to your Hive metastore (if you already have one) and access table metadata to reduce file listing when accessing information. This is popular for users who are migrating from a legacy Hadoop environment and beginning to run all their workloads using Spark."
I am not able to understand what it means. Someone please help me with examples for the above use case.
Spark being the latest tool in Hadoop ecosystem has connectivity with earlier Hadoop tools. Hive was the most popular until recent times. Most Hadoop platforms have data stored in Hive tables which can be accessed using Hive as a SQL engine. However, Spark can also do the same things.
So, the given statements mention that you can connect to Hive metastore (which contains information about existing tables, databases, their location, schema, file types, etc.) and then you can run similar Hive queries on them just like you would with Hive.
Below are two examples that you can do with spark once you can connect to Hive metastore.
spark.sql("show databases")
spark.sql("select * from test_db.test_table")
I hope this answers your question.
Previously I could work entirely within the spark.sql api to interact with both hive tables and spark data frames. I could query views registered with spark or the hive tables with the same api.
I'd like to confirm, that is no longer possible with hadoop 3.1 and pyspark 2.3.2? To do any operation on a hive table one must use the 'HiveWarehouseSession' api and not the spark.sql api. Is there any way to continue using the spark.sql api and interact with hive or will I have to refactor all my code?
hive = HiveWarehouseSession.session(spark).build()
hive.execute("arbitrary example query here")
spark.sql("arbitrary example query here")
It's confusing because the spark documentation says
Connect to any data source the same way
and specifically gives Hive as an example, but then the Hortonworks hadoop 3 documentation says
As a Spark developer, you execute queries to Hive using the JDBC-style HiveWarehouseSession API
These two statements are in direct contradiction.
The Hadoop documentation continues "You can use the Hive Warehouse Connector (HWC) API to access any type of table in the Hive catalog from Spark. When you use SparkSQL, standard Spark APIs access tables in the Spark catalog."
At least as of present, Spark.sql spark is no longer universal correct? and I can no longer seamlessly interact with hive tables using the same api?
Yep, correct. I'm using Spark 2.3.2 but I can no longer access to hive tables using Spark SQL default API.
From HDP 3.0, catalogs for Apache Hive and Apache Spark are separated, they are mutually exclusive.
As you mentioned you have to use HiveWarehouseSession from pyspark-llap library.
I have created a table, ztest7 in the default database in my hive. I am able to query it using beeline. In tableau, I can query it using a custom sql.
However the table does NOT show when I search for it.
Am I missing something here?
Tableau Desktop Version = v10.1.1
Hive = v2.0.1
Spark = v2.1.0
Best Regards
I have the same issue with Tableau Desktop 10 (mac) to Hive (2.1.1) via Spark SQL 2.1 (on centos 7 server)
This is what I got from Tableau Support:
In Tableau Desktop, the ability to connect to Spark SQL without a
defining a default schema is not currently built into the product.
As a preliminary step, to define a default schema, configure the Spark
SQL hivemetastore to utilize a SchemaRDD or DataFrame. This must be
defined in the Hive Metastore for Tableau Desktop to be able to access
it. Pure schema-less Spark RDD's can not be queried by Spark SQL
because of the lack of a schema. RDDs can be converted into
SchemaRDDs, which have additional schema metadata as Spark SQL
provides access to SchemaRDDs. When a SchemaRDD is created, it is only
available in the local namespace or context, and is unavailable to
external services accessing Spark through ODBC and the Spark Thrift
Server. For Tableau to have access, the SchemaRDD needs to be
registered in a catalog that is available outside of just the local
context; the Hive Metastore is currently the only supported service.
I don't know how to check/implement this.
PS: I'd have posted this as a comment because I am not allowed to as I am new to Stack Overflow.
In the file labeled Table on the left side of the screen, Try selecting contains, entering part of your table name and hitting enter
I ran into similar issue. In my case, I had loaded tables using HIVE but the tableau connection to the data source was made using Impala as shown in the image below.
To fix the issue of not seeing the tables in tableau dropdown, try running INVALIDATE METADATA database.table_name in the impala interface. This fixed the problem for me.
To know why this fixes the issue, refer this link.
Following this questions on Spark SQL I'm wondering if Spark SQL with the Cassandra connector is able to push down the UDF's present in the SQL query to Cassandra UDF (if it exists).
I tried to have a look at the source but I wasn't able to get a clear answer.
No, there is currently no support for pushing down udfs.
Currently we are building a reporting platform as a data store we used Shark. Since the development of Shark is stopped so we are in the phase of evaluating Spark SQL. Based on the use cases we have we had few questions.
1) We have data from various sources( MySQL, Oracle, Cassandra, Mongo). We would like to know how can we get this data into Spark SQL? Does there exist any utility which we can use? Does this utility support continuous refresh of data (sync of new add/update/delete on data store to Spark SQL?
2) Is the a way to create multiple database in Spark SQL?
3) For Reporting UI we use Jasper, we would like to connect from Jasper to Spark SQL. When we did our initial search we got to know currently there is no support for consumer to connect Spark SQL through JDBC, but in future releases you would like the add the same. We would like to know by when Spark SQL would have a stable release which would have JDBC Support? Meanwhile we took the source code from https://github.com/amplab/shark/tree/sparkSql but we had some difficulty in setting it up locally and evaluating it . It would be great if you can help us with setup instructions.(I can share the issue we are facing please let me know where can I post the error logs)
4) We would also require a SQL prompt where we can execute queries, currently Spark Shell provides SCALA prompt where SCALA code can be executed, from SCALA code we can fire SQL queries. Like Shark we would like to have SQL prompt in Spark SQL. When we did our search we found that in future release of Spark this would be added. It would be great if you can tell us which release of Spark would address the same.
as for
3) Spark 1.1 provides better support for SparkSQL ThriftServer interface, which you may want to use for JDBC interfacing. Hive JDBC clients that support v. 0.12.0 are able to connect and interface with such server.
4) Spark 1.1 also provides a SparkSQL CLI interface that can be used for entering queries. In the same fashion that Hive CLI or Impala Shell.
Please, provide more details about what you are trying to achieve for 1 and 2.
I can answer (1):
Apache Sqoop was made specifically to solve this problem for the relational databases. The tool was made for HDFS, HBase, and Hive -- as such it can be used to make data available to Spark, via HDFS and the Hive metastore.
http://sqoop.apache.org/
I believe Cassandra is available to SparkContext via this connector from DataStax: https://github.com/datastax/spark-cassandra-connector -- which I have never used.
I'm not aware of any connector for MongoDB.
1) We have data from various sources( MySQL, Oracle, Cassandra, Mongo)
You have to use different driver for each case. For cassandra there is datastax driver (but i encountered some compatibility problems with SparkSQL). For any SQL system you can use JdbcRDD. The usage is straightforward, look at the scala example:
test("basic functionality") {
sc = new SparkContext("local", "test")
val rdd = new JdbcRDD(
sc,
() => { DriverManager.getConnection("jdbc:derby:target/JdbcRDDSuiteDb") },
"SELECT DATA FROM FOO WHERE ? <= ID AND ID <= ?",
1, 100, 3,
(r: ResultSet) => { r.getInt(1) } ).cache()
assert(rdd.count === 100)
assert(rdd.reduce(_+_) === 10100)
}
But notion that it's just an RDD, so you should work with this data through map-reduce api, not in SQLContext.
Does there exist any utility which we can use?
There is Apache Sqoop project but it's in active development state. The current stable version even doesn't save files in parquet format.
Spark SQL is a capability of the Spark framework. It shouldn't be compared to Shark because Shark is a service. (Recall that with Shark, you run a ThriftServer that you can then connect to from your Thrift app or even ODBC.)
Can you elaborate on what you mean by "get this data into Spark SQL"?
There are a couple of Spark - MongoDB connectors:
- the mongodb connector for hadoop (which doesn't actually need Hadoop at all!) https://databricks.com/blog/2015/03/20/using-mongodb-with-spark.html
the Stratio mongodb connector https://github.com/Stratio/spark-mongodb
If your data is huge and need to perform a lot of transformations then Spark SQL can be used for ETL purpose, else presto could solve all your problems. Addressing your queries one by one:
As your data is in MySQL, Oracle, Cassandra, Mongo all these can be integrated in Presto as it has connectors https://prestodb.github.io/docs/current/connector.html for all these databases.
Once you install Presto in cluster mode you can query all these databases together in one platform, which also provides to join a table from Cassandra and other tables from Mongo, this flexibility is unparalleled.
Presto can be used to connect to Apache Superset https://superset.incubator.apache.org/ which is open source and provides all sets Dashboarding. Also Presto can be connected to Tableau.
You can install MySQL workbench with presto connecting details which helps in providing a UI for all your databases at one place.