Deep dive into enterprise data lake through Impala

Deep dive into enterprise data lake
through Impala
Evans Ye
2014.7.28
8/2/2014 Confidential | Copyright 2013 TrendMicro Inc. 1

Agenda
• Introduction to Impala
• Impala Architecture
• Query Execution
• Getting Started
• Parquet File Format
• ACL via Sentry

Introduction to
Impala

Impala
• General-purpose SQL query engine
• Support queries takes from milliseconds to
hours (near real-time)
• Support most of the Hadoop file formats
– Text, SequenseFile, Avro, RCFile, Parquet
• Suitable for data scientists or business
analysts

Why do we need it?

Current adhoc-query solution - Pig
• Do hourly count on akamai log
– A = load ‘/test_data/2014/07/20/00'
using PigStorage();
B = foreach (group A all) COUNT_STAR(A);
dump B;
– …
0% complete
100% complete
(194202349)

Using Impala
• No memory cache
– > select count(*) from test_data
where day=20140720 and hour=0
– 194202349
• with OS cache
• Do a further query:
– select count(*) from test_data where
day=20140720 and hour=00 and c='US';
– 41118019

Status quo
• Developed by Cloudera
• Open source under Apache License
• 1.0 available in 05/2013
• current version is 1.4
• connect via ODBC/JDBC/hue/impala-shell
• authenticate via Kerberos or LDAP
• fine-grained ACL via Apache Sentry

Benefits
• High Performance
– C++
– direct access to data (no Mapreduce)
– in-memory query execution
• Flexibility
– Query across existing data(no duplication)
– support multiple Hadoop file format
• Scalable
– scale out by adding nodes

Impala
Architecture

Impala Architecture
Datanode
Tasktracker
Regionserver
impala
daemon
NN, JT, HM
Active
NN, JT, HM
Standby
Datanode
Tasktracker
Regionserver
impala
daemon
Datanode
Tasktracker
Regionserver
impala
daemon
Datanode
Tasktracker
Regionserver
impala
daemon
State store
Catalog
Hive
Metastore

Components
• Impala daemon
– collocate with datanodes
– handle all impala internal requests related to query
execution
– User can submit request to impala daemon
running on any node and that node serve as
coordinator node
• State store daemon
– communicates with impala daemons to confirm
which node is healthy and can accept new work
• Catalog daemon
– broadcast metadata changes from impala SQL
statements to all the impala daemons

Fault tolerance
• No fault tolerance for impala daemons
– A node failed, the query failed
• state-store offline
– query execution still function normally
– can not update metadata(create, alter…)
– if another impala daemon goes down, then
entire cluster can not execute any query
• catalog offline
– can not update metadata

Query Execution

Getting Started

Impala-shell (sercure cluster)
• $ yum install impala-shell
• $ kinit –kt evans_ye.keytab evans_ye
• $ impala-shell --kerberos
--impalad IMPALA_HOST

Create and insert
• > create table t1 (col1 string, col2 int);
• > insert into t1 values (‘foo’, 10);
– only supports writing to TEXT and PARQUET
tables
– every insert creates 1 tiny hdfs file
– by default, the file will be stored under
/user/hive/warehouse/t1/
– use it for setting up small dimension table,
experiment purpose, or with HBase table

Create external table to read existing files
• > create external table t2
(col1 string, col2 int)
row format delimited fields terminated by ‘t’
location ‘/user/evans_ye/test_data’;
– location must be a directory
(for example, pig output directory)
– files to read:
• V /user/evans_ye/test_data/part-r-00000
• X /user/evans_ye/test_data/_logs/history
• X /user/evans_ye/test_data/20140701/00/part-r-00000
• no recursive

No recursive?
• Then how to add external data with folder
structure like this:
– /user/evans_ye/test_data/20140701/00
/user/evans_ye/test_data/20140701/01
…
…

Partitioning

Create the table with partitions
• > create external table t3
(col1 string, col2 int)
partitioned by (`date` int, hour tinyint)
row format delimited fields terminated by ‘t’;
• No need to specify the location on create

Add partitions into the table
• > alter table t3
add partition (`date`=20130330, hour=0)
location
‘/user/evans_ye/test_data/20130330/00‘;

Partition number
• thousands of partitions per table
– OK
• tens of thousands partitions per table
– Not OK

Compute table statistics
• > compute stats t3;
• > show table stats t3;
• Help impala to optimize join query:
broadcast join, partitioned join

Parquet File
Format

Parquet
• apache incubator project
• column-oriented file format
– compression is better since all the value would be the
same type
– encoding is better since value could often be the same
and repeated
– SQL projection can avoid unnecessary read and
decoding on columns
• Supported by Pig, Impala, Hive, MR and Cascading
• impala by default use snappy with parquet
• impala + parquet = google dremel
– dremel doesn’t support join
– impala doesn’t support nested data structure(yet)

Transform text files table into parquet format
• > create table t4 like t3 stored as parquet;
• > insert overwrite t4
partition (`date`, hour)
select * from t3

Using parquet in Pig
• $ yum install parquet
• $ pig
• > A = load ‘/user/hive/warehouse/t4’
using parquet.pig.ParquetLoader
as (x: chararray, y: int);
• > store A into ‘/user/evans_ye/parquet_out’
using parquet.pig.ParquetStorer;

ACL via

Sentry
• apache incubator project
• provide fine-grained role based
authorization
• currently integrates with Hive and Impala
• require strong authentication such as
kerberos

Enable Sentry for Impala
• turns on Sentry authorization for Impala
– add two lines into impala daemon’s
configuration file
(/etc/default/impala)
– auth-policy.ini  Sentry policy file
– server1  a symbolic name used in policy file
• all impala daemons must specify same server name

Sentry policy file example
• roles:
– on server1,
spn_user_role has permission to
read(SELECT) all tables in spn database
• groups
– evans_ye group has role spn_user_role

Sentry policy file example
• roles:
– evans_data has permission to access
/user/evans_ye
• allows you to add data under /user/evans_ye as
partitions
– foo_db_role can do anything in foo database
• create, alter, insert, drop

Impala 2014 Roadmap
• 1.4 (now available)
– order by without limit
• 2.0
– nested data types (structs, arrays, maps)
– disk-based joins and aggregations

Deep dive into enterprise data lake through Impala

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