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К этому устройству также есть другие инструкции:
Фрагмент инструкции
T
able
size
can
aect
concurrency
at
the
page
lev
el.
F
or
example,
if
a
small
table
o ccupies
only
one
page,
then
the
eect
of
a
page
lev
el
lo
c
k
is
the
same
as
lo
c
king
the
en
tire
table.
In
the
case
of
small
tables
where
frequen
t
access
is
needed
b
y
m
ultiple
transactions,
row
lev
el
lo
c
king
can
pro
vide
the
b est
concurrency
.
After
issuing
an
UPD
A
TE
ST
A
TISTICS
statement
on
a
table,
y
ou
can
query
the
SYSTEM.T
ABLE
view
to
determine
ho
w
man
y
pages
it
o ccupies.
T
able
lev
el
lo
c
king
serializes
access
to
the
table,
that
is,
forces
transactions
with
incompatible
lo
c
ks
to
op erate
on
a
table
one
at
a
time.
This
reduces
deadlo c
ks
b
y
k
eeping
other
users
from
accessing
the
table
un
til
the
transaction
is
committed
or
otherwise
terminated.
A
small
table
limits
concurrency
b
y
its
v
ery
nature
since
the
probability
is
high
that
man
y
users
will
w
an
t
to
access
the
limited
n
um
b er
of
pages
or
rows.
By
lo
c
king
a
small
table
at
the
table
lev
el,
y
ou
can
improv
e
p erformance
b
y
reducing
the
w
ork
of
retrying
deadlo c
k
ed
transactions.
On
larger
tables,
the
price
of
table
lev
el
lo
c
king
is
higher,
since
the
naturally
higher
concurrency
of
the
large
table
is
sacriced
to
serialization.
P
age
lev
el
lo
c
king
improv
es
concurrency
b
y
allo wing
m
ultiple
users
to
access
dieren
t
pages
in
the
same
table
concurren
tly
.
Ro
w
lev
el
lo
c
king
maximizes
concurrency
b
y
allo wing
m
ultiple
users
to
access
dieren
t
rows
in
the
same
table
at
the
same
time,
ev
en
on
the
same
page.
Because
ALLBASE/SQL
uses
a
buer
system
in
accessing
data
from
database
les,
k
eep
in
mind
that
the
system
can
actually
acquire
sev
eral
page
or
row
lo
c
ks,
one
at
a
time,
b efore
the
data
is
exp osed
to
the
user.
In
eect,
the
user's
transaction
obtains
and
releases
lo
c
ks
on
sets
of
pages
or
rows
at
a
time
as
it
mov
es
through
a
query
result.
This
is
b ecause
data
from
man
y
pages
and
rows
can
b e
required
to
ll
the
12K
tuple
buer.
Types
of
Locks
Lo c
ks
in
ALLBASE/SQL
can
b e
classied
in
to
the
follo wing
v
e
t
yp es,
listed
from
the
low
est
to
the
highest
lev
el
of
sev
erity:
In
ten
tion
Share
(IS):
Indicates
an
in
ten
tion
to
read
data
at
a
low
er
lev
el
of
granularit
y
.
An
IS
lo
c
k
on
a
PUBLIC
table
indicates
an
in
ten
tion
to
read
a
page.
An
IS
lo
c
k
on
a
PUBLICR
O
W
table
together
with
an
IS
lo
c
k
on
a
page
indicates
an
in
ten
tion
to
read
a
row
on
that
page.
When
a
need
to
read
data
at
a
low
er
lev
el
is
established,
ALLBASE/SQL
in
ternally
requests
an
IS
lo
c
k
at
the
higher
lev
el.
F
or
example,
after
an
IS
table
lo
c
k
has
b een
granted
on
a
PUBLIC
table,
requests
are
made
for
S
lo
c
ks
on
particular
pages.
In
the
case
of
a
PUBLICR
O
W
table,
after
IS
lo
c
ks
ha
v
e
b een
granted
on
b oth
table
and
page,
requests
are
made
for
S
lo
c
ks
on
particular
rows.
In
ten
tion
Exclusive
(IX):
Indicates
an
in
ten
tion
to
up date
or
mo
dify
data
at
a
low
er
lev
el
of
granularit
y
.
An
IX
lo
c
k
on
a
PUBLIC
table
indicates
an
in
ten
tion
to
mo
dify
data
on
a
page.
An
IX
lo
c
k
on
a
PUBLICR
O
W
table
together
with
an
IX
lo
c
k
on
a
page
indicates
an
in
ten
tion
to
mo
dify
a
row
on
that
page.
When
a
need
to
write
data
at
a
low
er
lev
el
is
established,
ALLBASE/SQL
in
ternally
requests
an
IX
lo
c
k
at
the
higher
lev
el.
F
or
example,
after
an
IX
table
lo
c
k
has
b een
granted
on
a
PUBLIC
table,
requests
are
made
for
X
lo
c
ks
on
particular
pages.
In
the
case
of
a
PUBLICR
O
W
table,
after
IX
lo
c
ks
ha
v
e
b een
granted
on
b oth
table
and
page,
requests
are
made
for
X
lo
c
ks
on
particular
rows.
Share
(S):
P
ermits
reading
b
y
other
transactions.
Share
and
In
ten
tion
Exclusive
(SIX):
Indicates
a
share
lo
c
k
at
the
curren
t
lev
el
and
an
in
ten
tion
to
up date
or
mo
dify
data
at
a
low
er
lev
el
of
granularit
y
.
SIX
lo
c
ks
are
placed
on
b oth
tables,
pages,
and
rows.
When
the
need
to
write
data
at
the
page
or
row
lev
el
is
established,
and
there
is
also
a
need
to
b e
able
to
read
ev
ery
page
in
the
table
without
its
Concurrency
Control
through
Locks
and
Isolation
Lev
els
5-11
...Эта инструкция также подходит к моделям:
Программное обеспечение - MPE/iX 6.5 Operating System (1.57 mb)