question Re: How the hive metastore works in Support Questions

How the hive metastore works

joncodin — Sun, 20 Mar 2016 23:19:03 GMT

I have some hive tables with data. And now I will use spark sql to query this data.

But Im not understanding the role of a Hive component in this process, the Hive Metastore.

The Hive Metastore stores all info about the tables. And we can execute spark sql queries because spark can interact with Hive Metastore.

But, how that works, its automatic? I have the hive tables with data, now to execute spark sql queries I need to create the Hive Metastore? Or its automatic? We need to do something?

Im relatively new in Hive and Im not understanding well this concept in this scenario.

Thanks!!

Re: How the hive metastore works

geko — Sun, 20 Mar 2016 23:39:12 GMT

Hi @John Cod ,

a good starting point for diving into Hive is: https://cwiki.apache.org/confluence/display/Hive/Home.

If you install your cluster including Hive, the Hive Metastore will be installed as well...it is more or less "the brain"

HTH, Gerd

Re: How the hive metastore works

joncodin — Mon, 21 Mar 2016 00:39:49 GMT

Thanks for your help, I already read that documentation, but I still have the doubt, because that link talks more about metastore configuration, but Im with conceptual doubts. Maybe I didnt explain well my doubt, We need the hive metastore to run queries with spark because spark will use that metastore to execute queries. But we need to configure that metastore? I already have the tables and data in tables in hive and I did not nothing about metastore. But I need to do? My doubt is really this: Im not understaning how this communication between spark and hive with metastore works and what we need to do that its not automatic...

Re: How the hive metastore works

aervits — Mon, 21 Mar 2016 00:46:42 GMT

Here's a document to explain the integration http://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.4.0/bk_spark-guide/content/ch_accessing-hive-tables.html

Re: How the hive metastore works

SQLShaw — Mon, 21 Mar 2016 01:12:00 GMT

@John Cod The Hive Metastore, also referred to as HCatalog is a relational database repository containing metadata about objects you create in Hive. When you create a Hive table, the table definition (column names, data types, comments, etc.) are stored in the Hive Metastore. This is automatic and simply part of the Hive architecture. The reason why the Hive Metastore is critical is because it acts as a central schema repository which can be used by other access tools like Spark and Pig. Additionally, through Hiveserver2 you can access the Hive Metastore using ODBC and JDBC connections. This opens the schema to visualization tools like PowerBi or Tableau.

The only configuration you have to be concerned about is the initial install when you decide what relational database to use. The default is ProgresSQL but for production we recommend using Oracle or a system which is already being backed up and secured. Hope this helps.

Re: How the hive metastore works

joncodin — Mon, 21 Mar 2016 05:52:36 GMT

Thank you, now its more clear!

Re: How the hive metastore works

vvaks — Mon, 28 Mar 2016 07:15:36 GMT

I like to think of the meta store as the definition of the structure you want to impose on the unstructured data that lives on HDFS. Not only column names and types but where rows and columns start/end on the format being queried.

Re: How the hive metastore works

dhanurangineni — Thu, 20 Jul 2017 11:15:29 GMT

thanks for the information, as you said Hive metastore is used by other tools like spark and pig..so does that mean without hive can't we use spark and pig to access the data?

Re: How the hive metastore works

dheer_vijji_rag — Thu, 20 Jul 2017 20:18:30 GMT

@John Cod

As given above Hive metastore holds the details related to metadata (columns, datatypes, compression, input and output formats and many more that includes the HDFS location of the table and Database as well) with this information any tools/services that connects with Hive will invoke a NameNode call to get the Metadata (about the files, directories and the corresponding blocks etc) which is pretty much needed for the jobs that will be launched by Hive.

Re: How the hive metastore works

AMIRAL — Wed, 24 Oct 2018 17:24:41 GMT

Link is down

Re: How the hive metastore works

AMIRAL — Wed, 24 Oct 2018 17:26:07 GMT

Is this further documented somewhere ?