Create table t1(id int)
I was firing above query on Hive 2.3.6 (MapR Hadoop Distribution 6.3.0).
Default hive engine was tez.
So after firing the query I was not able to see any TEZ application is launched on the yarn resource manager web ui
So I've changed the execution engine to MapReduce.
set hive.execution.engine=mr
And tried to run the same query again.
Same I was not able to see any MR application was launched on the yarn resource manager web ui
So my questions are how hive manage such types of queries?
And where the details of this queries are stored like application id, start time so on?
create table - is a metadata operation only, data is not being processed. It creates records in the metastore database, no distributed processing framework like Tez or MR is necessary for this, Yarn is not used.
Compiler translates DDL to the metastore query only if possible.
Also some simple DQL queries can be executed as metastore only if statistics exists and this feature is enabled: https://stackoverflow.com/a/41021682/2700344, without using Tez or MR.
Also small tables can be queried without distributed framework, using fetch-only task, see this: Why is Fetch task in Hive works faster than Map-only task?
Related
In a mapr cluster using yarn and tez engine, we need to query hive data from datastage using jdbc connector. In some cases we need to increase tez container size due to data size. We do that in before sql statement in a parallel job, and then we query data in main job statement.
The problem is the before sql statement SET hive.tez.container.size=3000 is taking hours, but the query to data is running fine (few seconds).
Could it be related to how busy is the cluster at that time? many jobs in the queue??
Don't think so because it always crashes in set statement, but never in select statement.
Thanks in advance!
I would suggest to use IBM provided Hive JDBC driver and Hive Connector stage which allows to set Hive parameters via built-in stage property.
When a DataStage job runs slow, it could be for several reasons, from what you are saying, setting hive.tez.container.size=3000 in before sql statement is what taking hours, I would suggest to look on Hive DB side while running DataStage job.
If you are not using IBM provided Hive JDBC driver, then it's better to engage official support of 3rd party Hive JDBC driver to enable JDBC driver tracing.
Is Hive and Impala integration possible?
After data processing in hive i want to store result data in impala for better read, is it possible?
If yes can you please share one example.
Both hive and impala, do not store any data. The data is stored in the HDFS location and hive an impala both are used just to visualize/transform the data present in the HDFS.
So yes, you can process the data using hive and then read it using impala, considering both of them have been setup properly. But since impala needs to be refreshed, you need to run the invalidate metadata and refresh commands
Impala uses the HIVE metastore to read the data. Once you have a table created in hive, it is possible to read the same and query the same using Impala. All you need is to refresh the table or trigger INVALIDATE METADATA in impala to read the data.
Hope this helps :)
Hive and impala are two different query engines. Each query engine is unique in terms of its architecture as well as performance. We can use hive metastore to get metadata and running query using impala. The common usecase is to connect impala/hive from tableau. If we are visualizing hive from tableau, we can get the latest data without any work around. If we keep on loading the data continuously, metadata will be updated as well. Impala does not aware of those changes. So we should run metadata invalidate query by connecting impalad to refresh its state and sync with the latest info available in metastore. So that user will get the same results as hive when the run the same query from tableau using impala engine.
There is no configuration parameter available now to run this invalidation query periodically. This blog reads well to execute meta data invalidation query through oozie scheduler periodically to handle such problems, Or simply we can set up a cronjob from the server itself.
This question already has an answer here:
What is the difference between hbase and hive? (Hadoop)
(1 answer)
Closed 5 years ago.
In my project, we are using Hadoop 2, Spark, Scala. Scala is the programming language and Spark is using here for analysing. we are using Hive and HBase both. I can access all details like file etc. of HDFS using Hive.
But my confusions are -
When I can able to performed all jobs using Hive, Then why HBase is required to store the data. Is it not an overhead?
What are the functionality of HIVE and HBase?
If we only used Hive, Then what should be the problem?
Can anyone please let me know.
When I can able to performed all jobs using Hive, Then why HBASE is required to store the data. Is it not a overhead?
What are the functionality of Hive and Hbase
HBase is No Sql database which stores the data in key value pair. Hive has integration with Hbase.Hbase HIve Integration
Advantage :- Hive queries over HBase. Think joins and a easy way to do aggregates and simple operations on your Hbase data.
Hbase gives you a scalable storage infrastructure that keeps data online. StumbleUpon uses Hbase for their live website. Hive is not a real-time query engine, so its data store could not be used for similar purposes. Hive over HBase gives you the benefit of both worlds.
If we only used Hive, Then what should be the problem?
If we will use Hive There is no problem . But in project there so many scenarios we have to consider .
Performance
Storage
Stability of used technology
Compatibility (Hive ware house is easily accessible for most of the Tools in Hadoop)
When I can able to performed all jobs using Hive, Then why HBase is
required to store the data. Is it not an overhead?
I can't say it's overhead or not. But HBase responds to requests in real-time as its database when it comes to Hive it runs jobs on MapReduce/Spark/Tez engines.
What are the functionality of Hive and HBase?
Hive:
It's a SQL-like language that gets translated into MapReduce/Spark/Tez jobs. it only runs batch processes on Hadoop. for more check this how Hive queries run on MapReduce engine
HBase:
It's key/value store database which runs on top of HDFS/S3(on AWS). It does real-time operations for requests.
If we only used Hive, Then what should be the problem?
As discussed If the query needs to process in real-time then HBase is the choice over Hive.
Hive installation guide says that Hive can be applied to RDBMS, my question is, sounds like Hive can exist without Hadoop, right? It's an independent HQL engineer that could work with any data source?
You can run Hive in local mode to use it without Hadoop for debugging purposes. See below url
https://cwiki.apache.org/confluence/display/Hive/GettingStarted#GettingStarted-Hive,Map-ReduceandLocal-Mode
Hive provided JDBC driver to query hive like JDBC, however if you are planning to run Hive queries on production system, you need Hadoop infrastructure to be available. Hive queries eventually converts into map-reduce jobs and HDFS is used as data storage for Hive tables.
I am trying to create an ORC table in Hive by importing from a text file in HDFS. I have tried multiple different ways, searched online for help, and regardless the insert job won't start.
I can get the text file to HDFS, I can read the text file to Hive, but I cannot convert from that to ORC.
I tried many different variations, including this one that can be used as a reference to this question:
http://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.3.0/bk_dataintegration/content/moving_data_from_hdfs_to_hive_external_table_method.html
I have a single-node HDP cluster (being used for development) - version:
HDP-2.3.2.0
(2.3.2.0-2950)
And here are the relevant service versions:
Service Version Status Description
HDFS 2.7.1.2.3 Installed Apache Hadoop Distributed File System
MapReduce2 2.7.1.2.3 Installed Apache Hadoop NextGen MapReduce (YARN)
YARN 2.7.1.2.3 Installed Apache Hadoop NextGen MapReduce (YARN)
Tez 0.7.0.2.3 Installed Tez is the next generation Hadoop Query Processing framework written on top of YARN.
Hive 1.2.1.2.3 Installed Data warehouse system for ad-hoc queries & analysis of large datasets and table & storage management service
What happens when I run a SQL like this (again, I've tried many variations including directly from online tutorials):
INSERT OVERWRITE TABLE mycars SELECT * FROM cars;
My job stays like this:
Total number of applications (application-types: [] and states:
[SUBMITTED, ACCEPTED, RUNNING]):1
Application-Id Application-Name Application-Type User Queue State Final-State Progress Tracking-URL
application_1455989658079_0002 HIVE-3f41161c-b806-4e7d-974e-c18e028d683f TEZ hive root.hive ACCEPTED UNDEFINED 0% N/A
And it just hangs there. (Literally, I've tried a 20 row sample table and let it run for hours before killing it).
I am by no means an Hadoop expert (yet) and am sure it's probably a config issue, but I have been unable to figure it out.
All other Hive operations I've tried, such as creating dropping tables, loading a file to a text table, selects, all work fine. It's just when I create an ORC table that it does this. And I need an ORC table for my requirement.
Any advice would be helpful.
Most of the time it has to do with increasing your Yarn Scheduling capacity, but if your resources are already capped you can also reduce the amount of memory requested by individual TEZ tasks, through adjusting the following property in TEZ configuration :
task.resource.memory.mb
In order to increase the Cluster's capacity you can do it in the configuration settings of YARN or directly through Ambari or Cloudera Manager
In order to monitor what is happening behind the hoods you can run Yarn Resource Manager UI and check the diagnostics tab of the specific Application there are useful explicit messages about resource allocation especially when the job is accepted and keeps pending.