cloudera impala

Scott Leberknight

Cloudera's

History lesson...

Google Map/Reduce paper (2004)

Cutt ing & Cafare l la create Hadoop (2005)

Google Dremel paper (2010)

Facebook creates Hive (2007)*

Cloudera announces Impala (October 2012)

HortonWorks' Stinger (February 2013)

Apache Drill proposal (August 2012)

* Hive => "SQL on Hadoop"

Write SQL queries

Translate into Map/Reduce job(s)

Convenient & easy

High-latency (batch processing)

What is Impala?

In-memory, distributed SQL query engine (no Map/Reduce)

Native code (C++)

Distributed(on HDFS data nodes)

Why Impala?

Interactive data analysis

Low-latency response(roughly, 4-100x Hive)

Deploy on existing Hadoop clusters

Why Impala? (cont'd)

Data stored in HDFS avoids...

...duplicate storage

...data transformation

...moving data

Why Impala? (cont'd)

SPEED!

Overview

impalad daemon runs on HDFS nodes

Queries run on "relevant" nodes

Supports common HDFS file formats

statestored, uses Hive metastore (for database metadata)

Overview (cont'd)

Does not use Map/Reduce

Not fault tolerant ! (query fails if any query on any node fails)

Submit queries via Hue/Beeswax Thrift API, CLI, ODBC, JDBC (future)

SQL Support

SELECT

Projection

UNION

INSERT OVERWRITE

INSERT INTO

ORDER BY(w/ LIMIT)

Aggregation

Subqueries(uncorrelated)

JOIN (equi-join only, subject to memory limitations)

(subset of Hive QL)

HBase Queries

Maps HBase tables via Hive metastore mapping

Row key predicates => start/stop row

Non-row key predicates => SingleColumnValueFilter

HBase scan translations:

(Very) Unscientific Benchmarks

9 queries, run in Impala Demo VM

Macbook Pro Retina, mid 201216GB RAM,4GB for VM (VMWare 5),Intel i7 2.6GHz quad-core processor

Hardware

No other load on system during queriesPseudo-cluster + Impala daemons

Benchmarks (cont'd)

(from simple projection queries to multiple joins, aggregation, multiple

predicates, and order by)

Impala vs. Hive performance

"TPC-DS" sample dataset(http://www.tpc.org/tpcds/)

Query "A"

select c.c_first_name, c.c_last_namefrom customer c limit 50;

Query "B"

select    c.c_first_name,    c.c_last_name,    ca.ca_city,    ca.ca_county,    ca.ca_state from customer c    join customer_address ca on c.c_current_addr_sk = ca.ca_address_sklimit 50;

Query "C"

select    c.c_first_name,    c.c_last_name,    ca.ca_city,    ca.ca_county,    ca.ca_statefrom customer c    join customer_address ca on c.c_current_addr_sk = ca.ca_address_skwhere lower(c.c_last_name) like 'smi%'limit 50;

Query "D"

select distinct cd_credit_ratingfrom customer_demographics;

Query "E"

select    cd_credit_rating,    count(*)from customer_demographicsgroup by cd_credit_rating;

Query "F"select    c.c_first_name,    c.c_last_name,    ca.ca_city,    ca.ca_county,    ca.ca_state,    cd.cd_marital_status,    cd.cd_education_statusfrom customer c    join customer_address ca        on c.c_current_addr_sk = ca.ca_address_sk    join customer_demographics cd        on c.c_current_cdemo_sk = cd.cd_demo_skwhere    lower(c.c_last_name) like 'smi%' and    cd.cd_credit_rating in ('Unknown', 'High Risk')limit 50;

Query "G"

select    count(c.c_customer_sk)from customer c    join customer_address ca        on c.c_current_addr_sk = ca.ca_address_sk    join customer_demographics cd        on c.c_current_cdemo_sk = cd.cd_demo_skwhere    ca.ca_zip in ('20191', '20194') and    cd.cd_credit_rating in ('Unknown', 'High Risk');

Query "H"select    c.c_first_name,    c.c_last_name,    ca.ca_city,    ca.ca_county,    ca.ca_state,    cd.cd_marital_status,    cd.cd_education_statusfrom customer c    join customer_address ca        on c.c_current_addr_sk = ca.ca_address_sk    join customer_demographics cd        on c.c_current_cdemo_sk = cd.cd_demo_skwhere    ca.ca_zip in ('20191', '20194') and    cd.cd_credit_rating in ('Unknown', 'High Risk')limit 100;

select     i_item_id,   s_state,   avg(ss_quantity) agg1,   avg(ss_list_price) agg2,   avg(ss_coupon_amt) agg3,   avg(ss_sales_price) agg4from store_salesjoin date_dim    on (store_sales.ss_sold_date_sk = date_dim.d_date_sk)join item    on (store_sales.ss_item_sk = item.i_item_sk)join customer_demographics    on (store_sales.ss_cdemo_sk = customer_demographics.cd_demo_sk)join store    on (store_sales.ss_store_sk = store.s_store_sk)where   cd_gender = 'M' and   cd_marital_status = 'S' and   cd_education_status = 'College' and   d_year = 2002 and   s_state in ('TN','SD', 'SD', 'SD', 'SD', 'SD')group by   i_item_id,   s_stateorder by   i_item_id,   s_statelimit 100;

Query "TPC-DS"

Query Hive (sec) # M/R jobs Impala (sec) x Hive perf.

A 12.4 1 0.21 59

B 30.9 1 0.37 84

C 29.6 1 0.33 91

D 22.8 1 0.60 38

E 22.5 1 0.52 44

F 66.4 2 1.56 43

G 83.0 3 1.33 62

H 66.1 2 1.50 44

TPC-DS 248.3 6 3.05 82

(remember, unscientific...)

Arch

itect

ure

Two daemonsimpaladstatestored

impalad on each HDFS data node

statestored - metadata

Thrift APIs

impalad

Query execution

Query coordination

Query planning

impalad

Query Coordinator

Query Planner

Query Executor

HDFS DataNode

HBase RegionServer

Queries performed in-memory

Intermediate data never hits disk!

Data streamed to clients

C++runtime code generationintrinsics for optimization

Execution engine:

statestored

Cluster membership

Metadata handling(scheduled for GA release)

Not a SPOF(single point of failure)

Metadata

Shares Hive metastore

Daemons cache metadata

Push to cluster via statestored(scheduled for GA release)

Create tables in Hive(then REFRESH impalad)

Next up - how queries work...

impalad

Query Coordinator

Query Planner

Query Executor

HDFS DataNode

HBase RegionServer

Client Statestore Hive Metastore

table metadata

table metadata (cached)

SQL query

impalad

Query Coordinator

Query Planner

Query Executor

HDFS DataNode

HBase RegionServer

impalad

Query Coordinator

Query Planner

Query Executor

HDFS DataNode

HBase RegionServer

Read directly from disk

Short-circuit reads

Bypass HDFS DataNode(avoids overhead of HDFS API)

impalad

Query Coordinator

Query Planner

Query Executor

HBase RegionServer

HDFS DataNode

Local Filesystem

Read directly

from disk

Current Limitations(as of beta version 0.6)

No join order optimization

No custom file formats or SerDes or UDFs

Limit required when using ORDER BY

Joins limited by memory of single node(at GA, aggregate memory of cluster)

Current Limitations(as of beta version 0.6)

No advanced data structures (arrays, maps, json, etc.)

No DDL (do in Hive)

Limited file formats (text, sequence w/ snappy/gzip compression)

Future - GA & beyond...

Structure types (structs, arrays, maps, json, etc.)

DDL support

Additional file formats & compression support

Columnar format(Parquet?)

"Performance" Metadata(via statestore)

JDBC

Join optimization(e.g. cost-based)

UDFs

Comparing...

Dremel is a scalable, interactive ad-hoc query system for analysis of read-only nested data. By combining multi-level execution trees and columnar data layout, it is capable of running aggregation queries over trillion-row tables in seconds. The system scales to thousands of CPUs and petabytes of data, and has thousands of users at Google.

Comparing Impala to Dremel

- http://research.google.com/pubs/pub36632.html

Comparing Impala to Dremel

Impala = Dremel features circa 2010 + join support, assuming columnar data format

(but, Google doesn't stand still...)

Dremel is production, mature

Basis for Google's BigQuery

Comparing Impala to Hive

Hive uses Map/Reduce -> high latency

Impala is in-memory, low-latency query engine

Sacrifices fault tolerance for performance

Comparing Impala to Others

Stinger

Apache Drill

Improve Hive performance (e.g. optimize execution plan)

Based on Dremel

In very early stages...

Support for analytics (e.g. OVER clause, window functions)

TEZ framework to optimize execution

Columnar file format

Review

In-memory, distributed SQL query engine

Integrates into existing HDFS

Not Map/Reduce

Focus is on performance

(native code)

References

Google Dremel - http://research.google.com/pubs/pub36632.html

Apache Drill - http://incubator.apache.org/drill/

TPC-DS dataset - http://www.tpc.org/tpcds/

Stinger Initiative - http://hortonworks.com/blog/100x-faster-hive/

Cloudera Impala resourceshttp://university.cloudera.com/onlineresources/introductionimpala.html

Cloudera Impala: Real-Time Queries in Apache Hadoop, For Real

http://blog.cloudera.com/blog/2012/10/cloudera-impala-real-time-queries-in-apache-hadoop-for-real/

Photo Attributions

Impala - http://www.flickr.com/photos/gerardstolk/5897570970/

Measuring tape - http://www.morguefile.com/archive/display/24850

Bridge frame - http://www.morguefile.com/archive/display/9699

Balance - http://www.morguefile.com/archive/display/93433

* All others are iStockPhoto (paid)

My Infoscott dot leberknight at nearinfinity dot com

twitter.com/sleberknight www.sleberknight.com/blog

www.nearinfinity.com/blogs/scott_leberknight/all/

scott dot leberknight at gmail dot com