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Cassandra Anti-Patterns
by Victor [email protected] - http://victoranjos.com
twitter.com/victorfanjos
This slideshow is for educational use only and is not affiliated with Jeopardy!® or Sony Pictures Digital Inc. Jeopardy! is a registered trademark of Jeopardy Productions, Inc. ©2005 Jeopardy Productions, Inc. All rights reserved.
JEOPARDY BOARDMath is Hard
tl;drRTFM
So 20th Century
On the catwalk Physics
$100 $100 $100 $100 $100
$200 $200 $200 $200 $200
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FINAL JEOPARDY
In a cluster of containing 5 nodes, I am the very important number of 3.
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What is Quorum?
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With Replication Factor of 2 (RF = 2) and
Consistency Level of Quorum (CL = Quorum), many operations were
failing when a single node was down because of this
simple math equation.
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What is 1 + 1 = 2?
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This was very high due to the CFHistograms
showing the majority of reads hitting hundreds of
SSTables
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What is Read Latency?
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Updating 90% of your rows with TTL = 0 to
purge data because disk space was running low
was this.
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What is a REALLY BAD IDEA?
(we will also accept “What is Incredibly Stupid?”)
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Adding this one word to session.execute in your
application code will greatly enhance your
application’s perceived performance.
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What is Async?(session.executeAsync)
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2GB is too small and 20GB is too large for this,
but people have used both in production and
had horrible things happen.
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What is Heap Size?
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The docs would recommend you to turn this off, however we can
go further and tell you it’s really a requirement.
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What is Swap?
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These should be used for atomicity, not performance.
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What are Batches?
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As of Cassandra 1.2, the best way to start thinking of wide or dynamic rows
was to use.
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What are Compound Keys?
(Can also accept “What are Collections?”)
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By setting up a DC in New York and another one in
sunny Rio de Janeiro, then using the Simple Snitch strategy, you are sure to
have this happen.
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What is everything timing out?
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This storage mechanism introduces a single point
of failure and totally negates the performance
benefits of Cassandra.
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What is a SAN?
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A commonly used RDBMS object that should only be
used on low-cardinality columns and not as a band-aid solution for a poorly designed data
model.
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What is a Secondary Index?
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Sometimes referred to as Brewer’s Theorem,
traditional RDBMS sits on one edge and most web
scale DBs sit on the other two or this triangle.
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What is CAP Theorem?
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Using these type of machines is an expensive
way to make your Cassandra clusters
inefficient.
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What are fat nodes?
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You should not use this to find out exactly how
many rows you have in your Cassandra database.
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What is SELECT COUNT(*)?
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Cassandra can often be referred to as a specific type of database, which
leads its data model paradigm.
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What is Column-oriented?
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Combining several fields to create one key.
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What are composite keys?
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When creating data models for Cassandra,
one should focus on this.
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What is Query Optimization?
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A concept borrowed from mathematical logic used
to perform extra writes on a CF, thus making
querying more flexible.
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What is a truth table?
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Data seems to disappear from collections due to
this.
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What is a 64K item limit?
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These can only spin so fast, so even though C*
was designed to minimize disk seeks, SSDs are still a better choice for low
read latency SLAs.
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What are rotational disks?
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Physics - $200 Question
These were timing out on 20GB partitions with
15MB slices.
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What are reads?
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You need to consider this constant when looking at the time for replication
across a WAN.
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What is the Speed of Light?
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Having more is better, specifically as of
Cassandra 2.1 since memtables are (nearly)
off heap.
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What is RAM?
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Using a 50MB network pipe to move 300MB
inserts is this.
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What is a really poor idea?
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Topic: Consensus
FINAL
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As of Cassanda 2.0, using the “IF NOT EXISTS”
directive at the end of an INSERT/UPDATE gives us.
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What are Lightweight Transactions?
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