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Table of Contents

DISCLAIMER: Hive has only been tested on unix(linux) and mac systems using Java 1.6 for now -
although it may very well work on other similar platforms. It does not work on Cygwin.
Most of our testing has been on Hadoop 0.20 - so we advise running it against this version even though it may compile/work against other versions

Hive introduction videos From Cloudera

Hive Introduction Video

Hive Tutorial Video

Installation and Configuration

Requirements

  • Java 1.6
  • Hadoop 0.20.x.

    Installing Hive from a Stable Release

Start by downloading the most recent stable release of Hive from one of the Apache download mirrors (see Hive Releases).

Next you need to unpack the tarball. This will result in the creation of a subdirectory named hive-x.y.z:

Set the environment variable HIVE_HOME to point to the installation directory:

Finally, add $HIVE_HOME/bin to your PATH:

Building Hive from Source

The Hive SVN repository is located here: http://svn.apache.org/repos/asf/hive/trunk

In the rest of the page, we use build/dist and <install-dir> interchangeably.

Running Hive

Hive uses hadoop that means:

  • you must have hadoop in your path OR
  • export HADOOP_HOME=<hadoop-install-dir>

In addition, you must create /tmp and /user/hive/warehouse
(aka hive.metastore.warehouse.dir) and set them chmod g+w in
HDFS before a table can be created in Hive.

Commands to perform this setup

I also find it useful but not necessary to set HIVE_HOME

To use hive command line interface (cli) from the shell:

Configuration management overview

  • Hive default configuration is stored in <install-dir>/conf/hive-default.xml
    Configuration variables can be changed by (re-)defining them in <install-dir>/conf/hive-site.xml
  • The location of the Hive configuration directory can be changed by setting the HIVE_CONF_DIR environment variable.
  • Log4j configuration is stored in <install-dir>/conf/hive-log4j.properties
  • Hive configuration is an overlay on top of hadoop - meaning the hadoop configuration variables are inherited by default.
  • Hive configuration can be manipulated by:
  • Editing hive-site.xml and defining any desired variables (including hadoop variables) in it
  • From the cli using the set command (see below)
  • By invoking hive using the syntax:
    • $ bin/hive -hiveconf x1=y1 -hiveconf x2=y2
      this sets the variables x1 and x2 to y1 and y2 respectively
  • By setting the HIVE_OPTS environment variable to "-hiveconf x1=y1 -hiveconf x2=y2" which does the same as above

    Runtime configuration

  • Hive queries are executed using map-reduce queries and, therefore, the behavior
    of such queries can be controlled by the hadoop configuration variables.
  • The cli command 'SET' can be used to set any hadoop (or hive) configuration variable. For example:

The latter shows all the current settings. Without the -v option only the
variables that differ from the base hadoop configuration are displayed

Hive, Map-Reduce and Local-Mode

Hive compiler generates map-reduce jobs for most queries. These jobs are then submitted to the Map-Reduce cluster indicated by the variable:

While this usually points to a map-reduce cluster with multiple nodes, Hadoop also offers a nifty option to run map-reduce jobs locally on the user's workstation. This can be very useful to run queries over small data sets - in such cases local mode execution is usually significantly faster than submitting jobs to a large cluster. Data is accessed transparently from HDFS. Conversely, local mode only runs with one reducer and can be very slow processing larger data sets.

Starting v-0.7, Hive fully supports local mode execution. To enable this, the user can enable the following option:

In addition, mapred.local.dir should point to a path that's valid on the local machine (for example /tmp/<username>/mapred/local). (Otherwise, the user will get an exception allocating local disk space).

Starting v-0.7, Hive also supports a mode to run map-reduce jobs in local-mode automatically. The relevant options are:

note that this feature is disabled by default. If enabled - Hive analyzes the size of each map-reduce job in a query and may run it locally if the following thresholds are satisfied:

  • The total input size of the job is lower than: hive.exec.mode.local.auto.inputbytes.max (128MB by default)
  • The total number of map-tasks is less than: hive.exec.mode.local.auto.tasks.max (4 by default)
  • The total number of reduce tasks required is 1 or 0.

So for queries over small data sets, or for queries with multiple map-reduce jobs where the input to subsequent jobs is substantially smaller (because of reduction/filtering in the prior job), jobs may be run locally.

Note that there may be differences in the runtime environment of hadoop server nodes and the machine running the hive client (because of different jvm versions or different software libraries). This can cause unexpected behavior/errors while running in local mode. Also note that local mode execution is done in a separate, child jvm (of the hive client). If the user so wishes, the maximum amount of memory for this child jvm can be controlled via the option hive.mapred.local.mem. By default, it's set to zero, in which case Hive lets Hadoop determine the default memory limits of the child jvm.

Error Logs

Hive uses log4j for logging. By default logs are not emitted to the
console by the CLI. The default logging level is WARN and the logs are stored in the folder:

  • /tmp/<user.name>/hive.log

If the user wishes - the logs can be emitted to the console by adding
the arguments shown below:

  • bin/hive -hiveconf hive.root.logger=INFO,console

Alternatively, the user can change the logging level only by using:

  • bin/hive -hiveconf hive.root.logger=INFO,DRFA

Note that setting hive.root.logger via the 'set' command does not
change logging properties since they are determined at initialization time.

Hive also stores query logs on a per hive session basis in /tmp/<user.name>/, but can be configured in hive-site.xml with the hive.querylog.location property.

Logging during Hive execution on a Hadoop cluster is controlled by Hadoop configuration. Usually Hadoop will produce one log file per map and reduce task stored on the cluster machine(s) where the task was executed. The log files can be obtained by clicking through to the Task Details page from the Hadoop JobTracker Web UI.

When using local mode (using mapred.job.tracker=local), Hadoop/Hive execution logs are produced on the client machine itself. Starting v-0.6 - Hive uses the hive-exec-log4j.properties (falling back to hive-log4j.properties only if it's missing) to determine where these logs are delivered by default. The default configuration file produces one log file per query executed in local mode and stores it under /tmp/<user.name>. The intent of providing a separate configuration file is to enable administrators to centralize execution log capture if desired (on a NFS file server for example). Execution logs are invaluable for debugging run-time errors.

Error logs are very useful to debug problems. Please send them with any bugs (of which there are many!) to hive-dev@hadoop.apache.org.

DDL Operations

Creating Hive tables and browsing through them

Creates a table called pokes with two columns, the first being an integer and the other a string

Creates a table called invites with two columns and a partition column
called ds. The partition column is a virtual column. It is not part
of the data itself but is derived from the partition that a
particular dataset is loaded into.

By default, tables are assumed to be of text input format and the
delimiters are assumed to be ^A(ctrl-a).

lists all the tables

lists all the table that end with 's'. The pattern matching follows Java regular
expressions. Check out this link for documentation http://java.sun.com/javase/6/docs/api/java/util/regex/Pattern.html

shows the list of columns

As for altering tables, table names can be changed and additional columns can be dropped:

Dropping tables:

Metadata Store

Metadata is in an embedded Derby database whose disk storage location is determined by the
hive configuration variable named javax.jdo.option.ConnectionURL. By default
(see conf/hive-default.xml), this location is ./metastore_db

Right now, in the default configuration, this metadata can only be seen by
one user at a time.

Metastore can be stored in any database that is supported by JPOX. The
location and the type of the RDBMS can be controlled by the two variables
javax.jdo.option.ConnectionURL and javax.jdo.option.ConnectionDriverName.
Refer to JDO (or JPOX) documentation for more details on supported databases.
The database schema is defined in JDO metadata annotations file package.jdo
at src/contrib/hive/metastore/src/model.

In the future, the metastore itself can be a standalone server.

If you want to run the metastore as a network server so it can be accessed
from multiple nodes try HiveDerbyServerMode.

DML Operations

Loading data from flat files into Hive:

Loads a file that contains two columns separated by ctrl-a into pokes table.
'local' signifies that the input file is on the local file system. If 'local'
is omitted then it looks for the file in HDFS.

The keyword 'overwrite' signifies that existing data in the table is deleted.
If the 'overwrite' keyword is omitted, data files are appended to existing data sets.

NOTES:

  • NO verification of data against the schema is performed by the load command.
  • If the file is in hdfs, it is moved into the Hive-controlled file system namespace.
    The root of the Hive directory is specified by the option hive.metastore.warehouse.dir
    in hive-default.xml. We advise users to create this directory before
    trying to create tables via Hive.

The two LOAD statements above load data into two different partitions of the table
invites. Table invites must be created as partitioned by the key ds for this to succeed.

The above command will load data from an HDFS file/directory to the table.
Note that loading data from HDFS will result in moving the file/directory. As a result, the operation is almost instantaneous.

SQL Operations

Example Queries

Some example queries are shown below. They are available in build/dist/examples/queries.
More are available in the hive sources at ql/src/test/queries/positive

SELECTS and FILTERS

selects column 'foo' from all rows of partition ds=2008-08-15 of the invites table. The results are not
stored anywhere, but are displayed on the console.

Note that in all the examples that follow, INSERT (into a hive table, local
directory or HDFS directory) is optional.

selects all rows from partition ds=2008-08-15 of the invites table into an HDFS directory. The result data
is in files (depending on the number of mappers) in that directory.
NOTE: partition columns if any are selected by the use of *. They can also
be specified in the projection clauses.

Partitioned tables must always have a partition selected in the WHERE clause of the statement.

Selects all rows from pokes table into a local directory

Sum of a column. avg, min, max can also be used. Note that for versions of Hive which don't include HIVE-287, you'll need to use COUNT(1) in place of COUNT(*).

GROUP BY

Note that for versions of Hive which don't include HIVE-287, you'll need to use COUNT(1) in place of COUNT(*).

JOIN

MULTITABLE INSERT

STREAMING

This streams the data in the map phase through the script /bin/cat (like hadoop streaming).
Similarly - streaming can be used on the reduce side (please see the Hive Tutorial for examples)

Simple Example Use Cases

MovieLens User Ratings

First, create a table with tab-delimited text file format:

Then, download and extract the data files:

And load it into the table that was just created:

Count the number of rows in table u_data:

Note that for versions of Hive which don't include HIVE-287, you'll need to use COUNT(1) in place of COUNT(*).

Now we can do some complex data analysis on the table u_data:

Create weekday_mapper.py:

Use the mapper script:

Note that if you're using Hive 0.5.0 or earlier you will need to use COUNT(1) in place of COUNT(*).

Apache Weblog Data

The format of Apache weblog is customizable, while most webmasters uses the default.
For default Apache weblog, we can create a table with the following command.

More about !RegexSerDe can be found here: http://issues.apache.org/jira/browse/HIVE-662

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