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From YouTube: CDS G/H (Day 2) - RBD: Database Performance
Description
https://wiki.ceph.com/Planning/CDS/CDS_Giant_and_Hammer_(Jun_2014)
25 June 2014
Ceph Developer Summit G/H
Day 2
RBD: Database Performance
B
B
So
generally,
that's
what
what
we
are
trying
to
hope
to
achieve
of
that
of
this
particular
blueprint
and
obviously
one
of
the
hidden
agenda.
The
ultimate
goal
is
to
see
how
we
can
leverage
ourselves
capability
to
run
database
on
a
really
really
wide
area
network,
rather
than
maybe
using
multi-site
to
do
a
replication.
Can
we
just
do
it
in
just
one
single
cluster
covering
the
whole
white
area
network,
for
example?
B
E
B
B
B
So
I
think
we
recently
actually
done
some
benchmark
with
postgres
in
our
little
testbed
that
we
have
and
we
found
that
the
performance
is
not
really
what
what
we
are
expecting
and
obviously
because
we
don't
have
the
luxury
of
having
ssds
and
whatnot.
We
are
just
doing
it
on
a
sata
stripe
for
our
osd.
So
what
we
really
hope
moving
forward
is:
are
there
any
other
people
within
this
community
that
are
willing
to
maybe
share
experiences
and
best
practices
to
to
to
look
at?
B
You
know
not
just
postgrads
that
we
are
using
yeah,
but
my
sequel,
no
sequel,
star
other
works.
So
so,
obviously,
once
we
have
some
of
these
things
tied
down,
then
maybe
we
can
move
forward
towards
some
use
case
for
for
wide
area
network
as
well.
So
so
I
think
our
first
step
is
at
least
to
figure
out
what
works
and
what
doesn't
work
and
what
needs
to
be
done.
A
Yes,
yeah,
I
think
think
the
database
performance
is
going
to
be
interesting
because
my
in
my
limited
understanding
of
what
the
databases
are
usually
doing,
they
usually
have
a
journal
file
where
they
have
like
a
stream
of
small,
writes
that
they're
f-syncing
or
using
direct
right
direct
io
to
lay
down
and
then
those
for
that.
For
that,
like
you,
know,
high
up
rate
of
small
rights,
those
are
with
the
general
striping
strategy.
A
Those
are
going
to
pile
up
on
a
single
object
which
could
potentially
be
a
problem,
at
least
for
high
performance
databases.
This
is
one
of
the
reasons
why
we
added
the
fancy
striping,
so
you
can
sort
of
spread
those
out
across.
You
know
shard
that
across
a
lot
of
objects.
On
the
other
hand,
you
don't
want
to
do
that
for
the
full
image,
because
that's
that'll,
probably
it'll,
tend
to
amplify
your
rights
when
they
span
striped
boundaries.
A
So
I
know
I
know
that
or
I
assume
that,
like
you
know,
big
databases
like
oracle
and
so
forth,
will
let
you
specify
a
separate
device
for
the
database
journal
from
all
the
other
data,
at
least
that's
my
assumption.
I'm
not,
I
actually
don't
know
if
that's
true,
but
I
assume
that
they
do
that.
I
don't
know
that
postgres
in
my
mysql
do
that
at
all,
though,
since
they're
sort
of
designed
to
run
on
traditional
file
systems.
A
Right,
well,
I'm
thinking
yeah
yeah,
I
think
for
for
for
sort
of
mid
size,
small
databases,
it's
not
going
to
make
a
big
difference
in
any
case
like
having
the
journal.
You
know
pound
on
one
object
for
a
while
and
then
handle
the
next
object
for
a
while,
and
it's
not
going
to
be
too
limiting,
especially
since
it's
pure
right
so
you're
not
doing
any
reads.
A
F
B
B
Like
some
kind
of
rubber
packages,
but
more
like
what
kind
of
things
that
we
can
work
on
items
that
we
can
work
on
in
sequence,
that
maybe
we
can
kind
of
feedback
to
the
community
and
say:
okay
hi
guys,
we
have
done
something
like
that.
I
think
this
is
a
kind
of
a
good
good
best
practices
that
you
can
start
off
with,
and
maybe
you
can
get
more
discussion
rolling
later
on.
D
We
did
some
tests
on
running
mongodb
on
rbd,
but
that
not
so
much
luck.
Performance
was
really
bad,
especially
since
mongodb
can
be
configured
to
run
multiple
charts
on
different
vms
and
the
set
replicating.
So
you
run
on
problems
like
have
multiple
vms
riding
through
the
same
pool,
so
you
get
yeah
with
replica
level
three,
for
example
the
data
written
nine
times,
or
something
like
that,
and
that's
not
really
performing
yeah.
D
So
so
you,
you
need
to
split,
split
these
over
different
pools
and
make
sure
the
pools
are
not
hitting
the
same
hardware
so
yeah
and
for
testing.
We
did
run
the
database
directly
on
real
hardware
and
trace
the
stuff
with
the
block
tools
and
replayed
it
on
the
vm
to
see
what
the
difference
really
is
between
real
hardware
and
leds.
A
I
wonder
if
the
the
way
to
sort
of
focus
in
on
what
the
what
the
specific
issues
are
and
how
to
how
to
best
address
them.
We
can
get
people
to
focus
on
like
one
particular
database
and
then
do
a
series
of
experiments
to
narrow
down
exactly
what
you
know
what
we
can
do
to
improve
it,
whether
it's
the
latency
on
the
right
ahead
log,
for
example.
A
You
know
figure
out
whether
it's
the
log
that's
deliberate,
that's
latency
sensitive,
which
is
what
I'm
guessing
or
whether
it's
the
the
background
activity
on
the
on
the
rest
of
the
file
system.
That's
the
problem,
or
mostly
at
least
and
then,
and
then
we
can
figure
out
whether
you
know.
Maybe
the
solution
is
that
in
when
you
want
good
database
performance.
You
have
you
know
two
pools
of
in
radios
where
one
of
them
is
backed
by
disc.
A
F
A
So
there
was
a
there
was
a
this
is
sort
of
a
side
discussion,
but
what
we're
talking
about
postgres?
There
was
a
long
discussion
at
the
linux
storage
and
file
system
summit
like
three
months
ago
about
post
performance
in
general
on
just
linux,
where
they
described
in
detail
what
the
issues
were,
and
it
basically
comes
down
to
they
want.
A
That
is
you
via
sync,
and
they
have
this
problem
where
they
have
to
like,
tell
the
kernel
sync
and
that
shows
a
whole
bunch
of
dirty
pages
down
to
the
ios
and
then
slows
down
their
their
red
head
log,
which,
even
though
they
don't
actually
care
when
it's
terrible,
they
just
need
to
know
that
it
is
sortable
whatever.
So
there's
this
whole,
so
I
think
postgre
struggles
in
general
just
because
the
kernel
isn't
sort
of
exposing
the
right
type
of
interfaces
for
it.
A
B
B
B
I
mean
I
mean
when,
when
we're
running
benchmarks,
some
of
the
times,
we
really
don't
know
what
kind
of
tools
we
can
actually
further
look
at
now
to
pick
up.
You
know
we,
we
have
the
benchmark
tools
which
we
are
using
right
now,
but
we
don't
don't
really
know
what
other
tools
we
can
actually
use
for
tracing
for
example,
or
not
figure
out
what
what
is
being
done
at
what
level,
but
we
just
we're
just
doing
pure
benchmarks.
B
A
B
E
That's
probably
going
to
another
level
of
the
file
system
as
well,
but
that
will
give
you
some
idea
of
and
you
can
use
as
another
tool
called
sequencer
which
you
can
use
to
visualize.
What
kind
of
patterns
are
going
at
the
disk
which
can
be
interesting
when,
if
you
see
I
see
like
the
journal
being
written
over
and
over
again-
and
there
are
random
rights
going
on
in
other
areas,.
C
A
So
I
think
it's
it's.
The
thing
I'm
most
interested
in
is
figuring
out
how
to
quantify
how
how
much
of
it
is
that
and
how
much
of
it
might
be
something
else
like.
Maybe
it's,
maybe
it's
the
that
the
barriers,
it's
periodically
doing
a
flush
and
we
have
a
whole
bunch
of
dirty
data
and
that's
the
thing
that's
slowing
it
down
like
it's
kind
of
hard
to
hard
to
say
I
wonder
actually,
sam
or
josh.
E
E
A
C
D
D
D
C
B
A
D
B
B
You
can
move
forward
and
see,
okay
guys
now
we
think
we
have
something
that
is
very
close
to
running
on
a
local
drive
or
at
least
a
local
sata
drive
nothing
fancy,
but
then
we
can
start
to
see
what
else
can
we
do
and
and
and
and
may
be
better
than
that?
It's
a
local
drive
things
like
that,
so
we
are
keeping
our
goal
quite
low
at
this
moment
of
time.
D
A
A
A
B
We
are
just
using
setup,
drives
yeah
for
both
the
data
and
general,
so
we
we
haven't
looked
at
using
ssd
yet,
but
I
think
one
of
the
ideas
later
on
is
is
maybe
we
can
separate
the
journal
and
the
data
away
first,
and
once
we
have
a
bit
of
budget
for
the
projects
we
can
hope
to.
We
hope
to
get
some
ssd
in
as
well.
A
A
I
think
you
should
definitely
follow
up
this
discussion
on
the
on
the
email
list
you
know
describe
describe
what
the
test
was
and
we
can
suggest
you
know
what
the
next
thing
to
try
might
be
and
seeing
what
what
effect
these
different
things
have
will
sort
of
lead
us
down
the
road
of
figuring
out.
You
know
if
it's
the
journal
or
if
it's
the
you
know
whatever
it's
a
caching
that
helps.