“Eventually consistent does not mean a day, minute or even second from now… in most cases, it is milliseconds!” This session will address Apache Cassandra’s tunable consistency model and cover how developers and companies should adopt a more Optimistic Software Design model.

1. Eventual
Consistency
!=
Hopeful
Consistency
Embracing
Op:mis:c
Design
in
the
Persistence
Layer

2. Who
am
I?
Christos
Kalantzis
Ne0lix
Inc.
Engineering
Manager
–
Cloud
Database
Engineering
@chriskalan
ckalantzis@neHlix.com
www.linkedin.com/in/christoskalantzis

3. C*
Replica:on
&
Consistency
Recap
• C*
is
eventually
Consistent
– That
means
it
WILL
get
there…eventually
• Eventually
is
not:
– A
day
from
now
– A
minute
from
now
– A
second
from
now
• In
most
cases
it
is
milliseconds

4. • C*
has
tunable
consistency
– All
– Quorum
– One
C*
Replica:on
&
Consistency
Recap

5. Remember
When...?
• In
early
2000s,
Read
was
scaled
out
by
adding
replica:on
Slaves
to
a
Master
DB.
• Writes
went
to
a
single
Master,
Reads
went
to
Slaves

6. Remember
When…?
• Slaves
could
lose
transac:ons

7. Remember
When…?
• No
“Repair”
func:on

8. Remember
When…?
• We
trusted
it
• We
s:ll
trust
it

9. C*
Consistency
Concerns
• “I
want
high
consistency
in
my
Reads/Writes
just
like
I
had
in
my
RDBMS
setup”
– You
never
really
had
it.
• “I
want
my
DB
to
catch
integrity
issues”
– We’ve
been
turning
FK
off
for
years!
• See
Rails,
Grails
&
other
MVC
frameworks
• Can
I
trust
that
C*
will
replicate
my
data
when
wri:ng
at
CL
1”

10. NeHlix
Experiment
• Created
a
mul:-­‐datacenter
C*
1.1.7
cluster
of
48
nodes
in
each
DC
• Put
load
on
C*
Cluster
– 100K
total
opera:ons
per
second
(50
K
in
each
DC)
• Wrote
1,000,000
records
at
CL1
in
one
DC
• Read
same
1,000,000
records
at
CL1
in
other
DC
• ALL
records
were
read
successfully
• You
can
trust
it!

11. NeHlix
Experiment

12. Op:mis:c
vs.
Pessimis:c
Design
• Pessimis:c
Design
– Design
with
high
consistency,
you
punish
your
users
99.9%
of
the
:me
• Higher
consistency
=
higher
latency
• Diminished
user
experience

13. Op:mis:c
vs.
Pessimis:c
Design
• Op:mis:c
Design
– Trust
your
data
store
• Know
your
business
and
your
applica:on
– Always
ask
yourself,
is
it
really
that
important?
• Handle
edge
cases
through
con:ngency
plans

14. Low
Consistency
Example
1

15. Low
Consistency
Example
2

16. Hurdles
Faced
• Engineers
are
stubborn!
– 1+1=2
..
not
eventually
2
• Middle
management
is
scared
– It’s
a
feat
you
convinced
them
to
use
C*
– Now
you
got
to
convince
them
to
accept
low
consistency?
• Engaging
Product
team
to
implement
some
type
of
con:ngency
plans

17. How
to
Overcome
those
Hurdles
• Prove
it
through
a
POC
• Show
them
the
benefits
of
an
improved
user
experience
– Its
all
about
the
user
• You
may
be
working
for
the
wrong
company
– We’re
hiring!
– jobs.neHlix.com

18. Q&A

19. Thank
you!