HBase At Meetup

HBase @ Meetup Gary Helmling – Lead SW Engineer

The Problem circa Jan 2009
Groups doing great things, but how do you find it all?
Wait til the next event
Click around (a lot)
Wanted to show what's happening in groups
Discussions, photos, new members, RSVPs, etc.
But requires 10 different queries!

The Solution
Show activity from all your groups in one place
real-time updates
better discovery of what's going on
find new ways to participate and get to know your groups

Challenges
Normalized schema
Each type of activity requires querying a separate table
already wasn't scaling at the group level
Query efficiency
Activity occurs at group level
Members can be in hundreds of groups
For member home page we need activity from all groups ordered by most recent
N subqueries by group ID merged back by descending timestamp

Options
De-normalize MySQL
Stuff different activity types into a common table (with different fields for different types of activity)
Duplicate entity data (or we're still doing N queries)
Start to lose a lot of the benefits of RDBMS
Query efficiency still a problem
Single system scaling limit
Something new
the Cloud
Google App Engine
Amazon SimpleDB
Hadoop/HBase
CouchDB
MongoDB
Voldemort
Cassandra

Why HBase?
We own infrastructure, no usage limits
Data model
Semi-structured data in HBase (easily handles multiple types in same table)
Time-series ordered
Scaling is built in (just add more servers)
But extra indexing is DIY
Very active developer community
Established, mature project (in relative terms!)
Matches our own toolset (java/linux based)

What is HBase?
Clone of Google's BigTable
Distributed (automatic partitioning)
Column-oriented
Semi-structured (columns can be added just by inserting)
Built-in versioning
Not an RDBMS
No joins
No SQL
Data usually not normalized
Transactions & built-in secondary indexes available (as contrib) but immature
Need to think differently about how you structure data
Denormalize your data where necessary
Structure data & row keys around common access

What is HBase? Data Storage
Table
Regions, defined by row [start key, end key)
Store, 1 per family
1+ Store Files (Hfile format on HDFS)
(table, rowkey, family, column, timestamp) = value
Everything is byte[]
Rows are ordered sequentially by key
Special tables: -ROOT-, .META.
Tell clients where to find user data

HBase Architecture Courtesy of Lars George see http://www.larsgeorge.com/2009/10/hbase-architecture-101-storage.html for more detail from http://www.larsgeorge.com/2009/10/hbase-architecture-101-storage.html

What is HBase? Data Access
Random access (Gets)
by rowkey only
Sequential reads (Scans)
starting row key
where you stop is as important as where you start
ending row key (optional)
server-side filter (optional)
Writes (Puts)
No insert vs. update distinction

How It Works Storing activity data in HBase
FeedItem : stores activity data for all types
keyed by group and descending timestamp
ch < chapterID > -ts < Long.MAX_VALUE–timestamp > - < type > - < entityID >
each row only contains data for that type
Row Key info: content: ch1261585-ts9223... item_type = chapter_greeting target_greeting = 8104438 greeting = “Hi, Gary” ch1261585-ts9223... item_type = new_discussion target_forum = 847743 target_thread = 7369603 title = “Improvements” body = “When a discussion is created...”
MemberFeedIndex : index of FeedItem rows from all of a member's groups
one row per member (keyed by member ID)
columns store refs to FeedItem row keys for that member's groups
TTL of 2 months expires old index values
Row Key item: 4679998 ch176399-ts9223370788400750807-mem-10044424 = new_member ch1261585-ts9223370787431124807-ptag-8525047 = photo_tag ...

How It Works MemberFeedIndex
Steps in displaying member home page feed
lookup member record in MemberFeedIndex by ID
grab the X most recent columns & values
use a time range for paging (older pages start with an earlier start time)
get each row from FeedItem using (column key as row key)
N gets, where N is number of items to display
populate some basic info about members and aggregate the results
still query MySQL for core entity info (member, group, event)

How it Works Secondary index tables
Still need to find rows by column values
tried “tableindexed” contrib (0.19 release), high CPU usage & contention on scans
decided to update to 0.20 release for other performance improvements
built secondary indexing into app layer
Separate table per indexed column
FeedItem info:actor_member indexed by FeedItem-by_actor_member
Index table rows keyed by column value and descending timestamp
<column value>-< Long.MAX_VALUE–timestamp >-<orig row key>
Zero pad numeric values (or big-endian representation) for correct byte ordering

How it Works Secondary index tables ex. FeedItem-by_actor_member Row Key info: __idx__: 0002851766-9223370783553935005- rowkey actor_member = 2851766 item_type = new_rsvp pub_date = row = ch1143475-ts9223370783553935005-rsvp-54704795 0004679998-9223370783650851832- rowkey actor_member = 4679998 item_type = new_discussion pub_date = row = ch1261585-ts9223370783650851832-disc-7369603 Row Key info: content: ch1143475-ts9223370783553935005-rsvp-54704795 actor_member = 2851766 item_type = new_rsvp pub_date = comment = “See you there” ch1261585-ts9223370783650851832-disc-7369603 actor_member = 4679998 item_type = new_discussion pub_date = title = “Next month” body = “...” indexes FeedItem

Interacting with HBase Meetup.Beeno package com.meetup.feeds.db; ... @HEntity (name="FeedItem") public class FeedItem implements Externalizable { ... @HRowKey public String getId() { return this.id; } public void setId(String id) { this.id = id; } @HProperty (family="info", name="actor_member", indexes = { @HIndex (date_col="info:pub_date", date_invert=true, extra_cols={"info:item_type"}) } ) public Integer getMemberId() { return this.memberId; } public void setMemberId(Integer id) { this.memberId = id; } Java Beans mapped to HBase tables

Interacting with HBase Services Base service class provides round-tripping based on annotations public class EntityService<T> { public T get( String rowKey ) throws HBaseException {…} public void save( T entity ) throws HBaseException {…} public void saveAll( List<T> entities ) throws HBaseException {…} public void delete( String rowKey ) throws HBaseException {…} public Query<T> query() throws MappingException {…} } easily extended for specific needs Almost all HBase interaction through service instances.

Interacting with HBase Queries Find all items related to a discussion FeedItemService service = new FeedItemService(DiscussionItem.class); Query query = service.query() .using( Criteria.eq("threadId", threadId) ); List items = query.execute(); Find all greetings from a given member FeedItemService service = new FeedItemService(GreetingItem.class); Query query = service.query() .using( Criteria.eq("memberId", memberId) ) .where( Criteria.eq(“type”, FeedItem.ItemType.CHAPTER_GREETING) ); List items = query.execute(); Simple Query API uses mappings and secondary index tables

Interacting with HBase Member Feed Retrieval // retrieve the member's index record HTable mfiTable = HUtil.getTable("MemberFeedIndex"); Get get = new Get( Bytes.toBytes(String.valueOf(memberId)) ); get.addFamily( Bytes.toBytes("item") ); Result r = mfiTable.get(get); FeedItemService service = new FeedItemService(); Set<IndexKey> sortedKeys = sortKeys(r); List<FeedItem> items = new ArrayList<FeedItem>(); // for each index col get the entity record for (IndexKey key : sortedKeys) { FeedItem item = service.get(key.getKey()); if (item != null) items.add(item); } // populate member and chapter info … Get latest activity from all a member's groups using MemberFeedIndex

HBase @ Meetup Issues along the way
Performance testing
Product targeting 3 of our highest traffic pages, simulating load is hard
Started with load scripts
Moved to testing with live traffic
Use AJAX calls to simulate requests
Selective enable for X% of traffic
Launched data collection/write traffic first
Allowed tweaking configuration before impacting user experience

HBase @ Meetup Issues along the way
High CPU / Concurrency issues
Updated to 0.20 release for performance gains across the board
Replaced “tableindexed” usage with application level secondary indexing
“Hot regions” - profile page hits small table every page load
Force split table to distribute across multiple servers
“Newest” region still handling high load
changed index keying to <value % 100>-<value>-<timestamp> for even distribution
I/O Heavy load / MemberFeedIndex table growing
Lowered MemberFeedIndex time-to-live to 2 months
Enabled LZO compression

HBase @ Meetup Current Status
Live traffic growing
Cluster handling ~2.5k – 3k request/sec
50+% still write traffic
~17% of page views hit HBase (for reads)
Expanding to 30% of page views in coming months
Meetup.Beeno now open-source on Github:
http://github.com/ghelmling/meetup.beeno
Next up
Continue tweaking
Site analytics

http://nosql.mypopescu.com	450
http://www.slideshare.net	57
http://www.meetup.com	10
http://bender	3
http://bender.radada.gruik.org	2
http://www.readpath.com	1
https://twitter.com	1

HBase At Meetup

by Gary Helmling on Feb 24, 2010

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