IBM Frozen Dessert Maker VERSION 9 Manual De Usuario
enabled,
DB2
will
automatically
run
the
RUNSTATS
utility
in
the
background
to
ensure
the
correct
statistics
are
collected
and
maintained.
Starting
in
DB2
Version
9,
automatic
statistics
collection
is
enabled
by
default
when
a
new
database
is
created.
The
performance
impact
of
automatic
statistics
collection
is
minimized
in
several
ways:
v
Statistic
collection
is
performed
using
throttled
RUNSTATS.
Throttling
controls
the
amount
of
resources
consumed
by
the
RUNSTATS
utility
based
on
current
database
activity:
as
database
activity
increases,
the
RUNSTATS
utility
runs
more
slowly,
reducing
its
resource
demands.
v
Only
the
minimal
set
of
statistics
for
optimizing
performance
are
collected.
This
is
achieved
through
the
use
of
statistics
profiling
which
uses
information
about
previous
database
activity
to
determine
which
statistics
are
required
by
the
database
workload,
and
how
quickly
those
statistics
will
become
out
of
date
given
the
type
of
activity
in
the
database.
v
Only
tables
with
high
levels
of
activity
(measured
through
the
number
of
updates,
deletes
and
inserts)
are
considered
for
statistic
collection.
Large
tables
(consisting
of
more
than
4000
pages)
are
also
sampled
to
determine
whether
the
high
table
activity
has
indeed
changed
the
statistics.
Statistics
for
these
large
tables
are
only
collected
if
warranted.
v
The
RUNSTATS
utility
is
automatically
scheduled
to
execute
during
the
optimal
maintenance
window
specified
in
your
maintenance
policy
definition.
This
policy
also
specifies
the
set
of
tables
that
are
within
the
scope
of
the
automatic
statistics
collection,
further
minimizing
unnecessary
resource
consumption.
v
While
automated
statistic
collection
is
being
performed,
the
affected
tables
are
still
available
for
regular
database
activity
(updates,
inserts,
deletes)as
if
RUNSTATS
were
not
running
on
the
table.
Related
concepts:
v
“Automatic
features
enabled
by
default”
in
Administration
Guide:
Planning
v
“Collecting
statistics
using
a
statistics
profile”
in
Performance
Guide
Related
tasks:
v
“Using
automatic
statistics
collection”
in
Performance
Guide
Related
reference:
v
“RUNSTATS
command
using
the
ADMIN_CMD
procedure”
in
Administrative
SQL
Routines
and
Views
v
“auto_maint
-
Automatic
maintenance
configuration
parameter”
in
Performance
Guide
v
“util_impact_lim
-
Instance
impact
policy
configuration
parameter”
in
Performance
Guide
v
“RUNSTATS
command”
in
Command
Reference
Chapter
6.
Automatic
maintenance
37