Information Technology Reference
In-Depth Information
Algorithm 11.2
Secondary-index update in procedure
insert
.T;x;y;
v
/
insert-into-page
.T;p;x;y;
v
/
if
the secondary index is under construction
then
n
1
U
NDO
-N
EXT
-LSN.T /
if
x<
Cursor
then
unlatch-and-unfix
.p; p
0
/
unlock
.T; x
0
; X; short-duration/
q the last page of the side file (allocating one if needed)
fix-and-write-latch
.q/
append the record .
ix-I
;y;x;p/into page q
log
.n
2
;hT;
append-to-side-file
;q;
ix-I
;y;x;p;n
1
i/
P
AGE
-LSN.q/ n
2
unlatch-and-unfix
.q/
else
{x>
Cursor
}
unlatch-and-unfix
.p; p
0
/
unlock
.T; x
0
; X; short-duration/
log
.n
2
;hT;
no-append-to-side-file
;
ix-I
;y;x;p;n
1
i/
end if
U
NDO
-N
EXT
-LSN.T / n
2
else if
the secondary index is available
then
unlatch-and-unfix
.p; p
0
/
unlock
.T; x
0
; X; short-duration/
insert-index-record
.T;y;x;p/
else
{the secondary index is neither available nor under construction}
unlatch-and-unfix
.p; p
0
/
unlock
.T; x
0
; X; short-duration/
end if
To accomplish the above, the sequence of calls
insert-into-page
.T;p;x;y;
v
/
unlatch-and-unfix
.p; p
0
/
unlock
.T; x
0
; X; short-duration/
at the end of the call
insert
.T;x;y;
v
/ must be replaced by the statements given
as Algorithm
11.2
. Here the short-duration X lock on the key x
0
next to x can
be released immediately after unlatching the page p and the next page p
0
,before
performing the actions specific to the secondary index.
In Algorithm
11.2
, it is essential that the data page p that receives the inserted
tuple is kept write-latched during the reading of the current value of
Cursor
, because
then the extraction process cannot advance its scan past page p, if it has not done so
before the page was write-latched for the insert action by T .IfT observes that x>
Cursor
, it unlatches p and writes a
no-append-to-side-file
log record, after which the
extraction process will in due time get a read latch on p when the scan has advanced
at that page and hence will capture the insertion. On the other hand, it is also correct
to unlatch p immediately after observing that x<
Cursor
before appending the
record to the side file, because in that case the scan has already advanced past the
page. We also note that the case x
D
Cursor
is impossible.
