The Apache Cassandra storage engine
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©2012 DataStax The Apache Cassandra storage engine Sylvain Lebresne 1 NoSQL matters 2012
Transcript of The Apache Cassandra storage engine
©2012 DataStax
The Apache Cassandra storage engine
Sylvain Lebresne
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NoSQL matters 2012
©2012 DataStax
• Sylvain Lebresne
• @pcmanus
About me
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1. What is Apache Cassandra
2. Data Model
3. The storage engine
©2012 DataStax
1. What is Apache Cassandra
2. Data Model
3. The storage engine
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about:project• Distributed data store aimed at big data.
• Apache project since 2010.
• Version 1.1 released last month.• Proven in production (Netflix, Twitter, Reddit,
Cisco, ...). Largest know cluster has over 300TB in over 400 machines.
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Apache Cassandra
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Apache CassandraA database:
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Apache CassandraA database:• distributed / decentralized
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Apache CassandraA database:• distributed / decentralized• replicated & durable
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Apache CassandraA database:• distributed / decentralized• replicated & durable• scalable / elastic
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Apache CassandraA database:• distributed / decentralized• replicated & durable• scalable / elastic
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Apache CassandraA database:• distributed / decentralized• replicated & durable• scalable / elastic• fault-tolerant / no SPOF
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Apache CassandraA database:• distributed / decentralized• replicated & durable• scalable / elastic• fault-tolerant / no SPOF• highly available
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Apache CassandraA database:• distributed / decentralized• replicated & durable• scalable / elastic• fault-tolerant / no SPOF• highly available• data center aware
US Europe
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1. What is Apache Cassandra
2. Data Model
3. The storage engine
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• Not SQL (no transaction, nor joins) but more than Key/Value.
• Inspired by Google BigTable
• Column families based.
Data Model
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©2012 DataStaxUsers
Ex: user profiles
birth_year 1994
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fname Justin
lname Bieber
“For each user, holds profile infos”
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©2012 DataStaxUsers
Ex: user profiles
birth_year 1994
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fname Justin
lname Bieber
birth_year 1978
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email [email protected]
fname Ashton
lname Kutcher
“For each user, holds profile infos”
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©2012 DataStaxTimeline
Ex: user’s Tweets
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“For each user, tweets he has made”
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©2012 DataStaxTimeline
Ex: user’s Tweets
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0 @LiveLoveKary glad you had a good birthday #muchlove
“For each user, tweets he has made”
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©2012 DataStaxTimeline
Ex: user’s Tweets
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0 @LiveLoveKary glad you had a good birthday #muchlove
1 @NickDeMoura happy bday my dude.
“For each user, tweets he has made”
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©2012 DataStaxTimeline
Ex: user’s Tweets
50e8-e29b
0 @LiveLoveKary glad you had a good birthday #muchlove
1 @NickDeMoura happy bday my dude.
2 @MickyArison @miamiHEAT thanks for the gam tonight
“For each user, tweets he has made”
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©2012 DataStaxTimeline
Ex: user’s Tweets
50e8-e29b
0 @LiveLoveKary glad you had a good birthday #muchlove
1 @NickDeMoura happy bday my dude.
2 @MickyArison @miamiHEAT thanks for the gam tonight
3 still a little tired. back in the studio today with Timbaland
“For each user, tweets he has made”
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There’s more• Secondary indexes
• Distributed counters
• Composite columns
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1. What is Apache Cassandra
2. Data Model
3. The storage engine
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• Writes are harder than reads to scale
• Spinning disks aren’t good with random I/O
• Goal: minimize random I/O
Goal
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A write’s journey
Memory
Hard drive
Memtable
Commit log
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write( , )k1 c1:v1
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A write’s journey
Memory
Hard drive
Memtable
write( , )k1 c1:v1
Commit log
k1 c1:v1
k1 c1:v1
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A write’s journey
Memory
Hard drive
k1 c1:v1
k1 c1:v1
ack
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A write’s journey
Memory
Hard drive
k1 c1:v1
k1 c1:v1
write( , )k2 c1:v1 c2:v2
k2 c1:v1 c2:v2
k2 c1:v1 c2:v2
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A write’s journey
Memory
Hard drive
k1 c1:v1
k1 c1:v4 c2:v2
write( , )k1 c1:v4 c3:v3
k2 c1:v1 c2:v2
c3:v3
c2:v2
k2 c1:v1 c2:v2
k1 c1:v4 c3:v3
c2:v2
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A write’s journey
Memory
Hard drive
SSTable
flush
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
index
cleanup
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A write’s journey
Memory
Hard drive
k2 c1:v2 c3:v3
k1 c1:v5 c4:v4
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
index
more updates
k1 c1:v5 c4:v4
k2 c1:v2 c3:v3
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A write’s journey
Memory
Hard drive
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
indexk1 c1:v5 c4:v4
k2 c1:v2 c3:v3
index
flush
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Writes properties• No reads or seeks
• Only sequential I/O
• Immutable SSTables: easy snapshots
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A read’s journey
Memory
Hard drive
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
indexk1 c1:v5 c4:v4
k2 c1:v2 c3:v3
index
read( )k1
?
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A read’s journey
Memory
Hard drive
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
index
k1 c1:v5 c4:v4
k2 c1:v2 c3:v3
index
k1
merge
c1:v5 c2:v2 c3:v3 c4:v4
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Compaction
• Goal: keep the number of SSTables low
• Merge sort against multiple sstables
• Sequential I/O
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Compaction
• Goal: keep the number of SSTables low
• Merge sort against multiple sstables
• Sequential I/O
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
index
k1 c1:v5 c4:v4
k2 c1:v2 c3:v3
index
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Compaction
• Goal: keep the number of SSTables low
• Merge sort against multiple sstables
• Sequential I/O
k1 c1:v4 c2:v2
k2 c1:v1 c2:v2
c3:v3
index
k1 c1:v5 c4:v4
k2 c1:v2 c3:v3
indexk1 c1:v5 c2:v2
k2 c1:v2 c2:v2
c3:v3
indexc4:v4
c3:v3
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SSTables
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BF Index SummaryMemoryDisk
k1 k2 k3
k1
312 0 ...
Index
Data
Col. BF Col. Index c1:v4 c2:v2 c3:v3 ... k2 Col. BF ...
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Optimizations• Row Cache
• Bloom filters: eliminates whole SSTable
• Key Cache• Rows & Columns Indexes
• ...
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Other features
• Compression
• Checksums
• Time to live
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QUESTIONS?
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• http://cassandra.apache.org/
• http://wiki.apache.org/cassandra/
• http://www.datastax.com/docs/1.0
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