HBase, Hadoop World NYC

Ryan Rawson, Stumbleupon.com, su.prJonathan Gray, Streamy.com

A presentation in 2 parts

Part 1

About Me

•Ryan Rawson

•Senior Software Developer @ Stumbleupon

•HBase committer, core contributor

Stumbleupon

•Uses HBase in production

•Behind features of our su.pr service

•More later

Adventures with MySQL

•Scaling MySQL hard, Oracle expensive (and hard)

•Machine cost goes up faster speed

•Turn off all relational features to scale

•Turn off secondary (!) indexes too! (!!)

MySQL problems cont.

•Tables can be a problem at sizes as low as 500GB

•Hard to read data quickly at these sizes

•Future doesn’t look so bright as we contemplate 10x sizes

•MySQL master becomes a problem...

Limitations of masters

•What if your write speed is greater than a single machine?

•All slaves must have same write capacity as master (can’t cheap out on slaves)

•Single point of failure, no easy failover

•Can (sort of) solve this with sharding...

Sharding

Sharding problems

•Requires either a hashing function or mapping table to determine shard

•Data access code becomes complex

•What if shard sizes become too large...

Resharding!

What about schema changes?

•What about schema changes or migrations?

•MySQL not your friend here

•Only gets harder with more data

HBase to the rescue

•Clustered, commodity(ish) hardware

•Mostly schema-less

•Dynamic distribution

•Spreads writes out over the cluster

What is HBase?

•HBase is an open-source distributed database, inspired by Google’s bigtable

•Part of the Hadoop ecosystem

•Layers on HDFS for storage

•Native connections to map reduce

HBase storage model

•Column-oriented database

•Column name is arbitrary data, can have large, variable, number of columns per row

•Rows stored in sorted order

•Can random read and write

Tables

•Table is split into roughly equal sized “regions”

•Each region is a contiguous range of keys, from [start, to end)

•Regions split as they grow, thus dynamically adjusting to your data set

Server architecture

•Similar to HDFS:

•Master = Namenode (ish)

•Regionserver = Datanode (ish)

•Often run these alongside each other!

Server Architecture 2

•But not quite the same, HBase stores state in HDFS

•HDFS provides robust data storage across machines, insulating against failure

•Master and Regionserver fairly stateless and machine independent

Region assignment

•Each region from every table is assigned to a Regionserver

•The master is responsible for assignment and noticing if (when!) regionservers go down

Master Duties

•When machines fail, move regions from affected machines to others

•When regions split, move regions to balance cluster

•Could move regions to respond to load

•Can run multiple backup masters

What Master does NOT do

•Does not handle any write requests (not a DB master!)

•Does not handle location finding requests

•Not involved in the read/write path!

•Generally does very little most the time

Distributed coordination

•To manage master election and server availability we use ZooKeeper

•Set up as a cluster, provides distributed coordination primitives

•An excellent tool for building cluster management systems

Scaling HBase

•Add more machines to scale

•Base model (bigtable) scales past 1000TB

•No inherent reason why HBase couldn’t

What to store in HBase?

•Maybe not your raw log data...

•... but the results of processing it with Hadoop!

•By storing the refined version in HBase, can keep up with huge data demands and serve to your website

•Provides a real time, structured storage layer that integrates on your existing Hadoop clusters

•Provides “out of the box” hookups to map-reduce.

•Uses the same loved (or hated) management model as Hadoop

HBase & Hadoop

HBase @

Stumbleupon & HBase

•Started investigating the field in Jan ’09

•Looked at 3 top (at the time) choices:

•Cassandra

•Hypertable

•HBase

cassandra didnt work, didnt like data model- hypertable fast but community and project viability (no major users beyond zvents)- hbase local and good community

cassandra didnt work, didnt like data model- hypertable fast but community and project viability (no major users beyond zvents)- hbase local and good community

Stumbleupon & HBase

•Picked HBase:

•Community

•Features

•Map-reduce, cascading, etc

•Now highly involved and invested

su.pr marketing

•“Su.pr is the only URL shortener that also helps your content get discovered! Every Su.pr URL exposes your content to StumbleUpon's nearly 8 million users!”

su.pr tech features

•Real time stats

•Done directly in HBase

•In depth stats

•Use cascading, map reduce and put results in hbase

su.pr web access

•Using thrift gateway, php code accesses HBase

•No additional caching other than what HBase provides

Large data storage

•Over 9 billion rows and 1300 GB in HBase

•Can map reduce a 700GB table in ~ 20 min

•That is about 6 million rows/sec

•Scales to 2x that speed on 2x the hardware

Micro read benches

•Single reads are 1-10ms depending on disk seeks and caching

•Scans can return hundreds of rows in dozens of ms

Serial read speeds

•A small table

•A bigger table

•(removed printlns from the code)

Deployment considerations

•Zookeeper requires IO to complete ops

•Consider hosting on dedicated machines

•Namenode and HBase master can co-exist

What to put on your nodes

•Regionserver requires 2-4 cores and 3gb+

•Can’t run HDFS, HBase, maps, reduces on a 2 core system

•On my 8 core systems I run datanode, regionserver, 2 maps, 2 reduces

Garbage collection

•GC tuning becomes important.

•Quick tip: use CMS, use -Xmx4000m

•Interested in G1 (if it ever stops crashing)

Batch and interactive

•These may not be compatible

•Latency goes up with heavy batch load

•May need to use 2 clusters to ensure responsive website

Part 2

HBase @ Streamy

•History of Data

•RDBMS Issues

•HBase to the Rescue

•Streamy Today and Tomorrow

•Future of HBase

About Me

•Co-Founder and CTO of Streamy.com

•HBase Committer

•Migrated Streamy from RDBMS to HBase and Hadoop in June 2008

History of DataThe Prototype

•Streamy 1.0 built on PostgreSQL

‣All of the bells and whistles

•Powered by single low-spec node

‣8 core / 8 GB / 2TB / $4k

Functionally powerful, Woefully slow

History of DataThe Alpha

•Streamy 1.5 built on optimized PostgreSQL

‣Remove bells and whistles, add partitioning

•Powered by high-powered master node

‣16 core / 64 GB / 15x146GB 15k RPM / $40k

Less powerful, still slow... Insanely expensive

History of DataThe Beta

•Streamy 2.0 built entirely on HBase

‣Custom caches, query engines, and API

•Powered by 10 low-spec nodes

‣4 core / 4GB / 1TB / $10k for entire cluster

Less functional but fast, scalable, and cheap

RDBMS Issues

•Poor disk usage patterns

•Black box query engine

•Write speed degrades with table size

•Transactions/MVCC unnecessary overhead

•Expensive

The Read Problem•View 30 newest unread stories

from blogs

‣Not RDBMS friendly, no early-out

‣PL/Python heap-merge hack helped

‣We knew what to do but DB didn’t listen

The Write Problem

•Rapidly growing items table

‣Crawl index from 1k to 100k feeds

‣Indexes, static content, dynamic statistics

‣Solutions are imperfect

RDBMS Conclusions

•Enormous functionality and flexibility

‣ But you throw it out the door at scale

•Stripped down RDBMS still not attractive

•Turned entire team into DBAs

•Gets in the way of domain-specific optimizations

What We Wanted

•Transparent partitioning

•Transparent distribution

•Fast random writes

•Good data locality

•Fast random reads

What We Got

•Transparent partitioning

•Transparent distribution

•Fast random writes

•Good data locality

•Fast random reads

Regions

RegionServers

MemStore

Column Families

HBase 0.20

What Else We Got

•Transparent replication

•High availability

•MapReduce

•Versioning

•Fast Sequential Reads

HDFS

No SPOF

Input/OutputFormats

Column Versions

Scanners

HBase @ Streamy Today

HBase @ Streamy Today

•All data stored in HBase

•Additional caching of hot data

•Query and indexing engines

•MapReduce crawling and analytics

•Zookeeper/Katta/Lucene

HBase @ Streamy Tomorrow

•Thumbnail media server

•Slave replication for Backup/DR

•More Cascading

•Better Katta integration

•Realtime MapReduce

HBase on a Budget

•HBase works on cheap nodes

‣But you need a cluster (5+ nodes)

‣$10k cluster has 10X capacity of $40k node

•Multiple instances on a single cluster

•24/7 clusters + bandwidth != EC2

Lessons Learned•Layer of abstraction helps

tremendously

‣Internal Streamy Data API

‣Storage of serialized types

•Schema design is about reads not writes

•What’s good for HBase is good for Streamy

What’s Next for HBase

•Inter-cluster / Inter-DC replication

‣Slave and Multi-Master

•Master rewrite, more Zookeeper

•Batch operations, HDFS uploader

•No more data loss

‣Need HDFS appends

HBase Information

•Home Page http://hbase.org

•Wiki http://wiki.apache.org/hadoop/Hbase

•Twitter http://twitter.com/hbase

•Freenode IRC #hbase

•Mailing List hbase-user@hadoop.apache.org