Distributed Transactions - Transaction Processing - page 313

Algorithm 13.8 Tracking updates from the primary database system
r the next log record from the primary system
while r is a log record with LSN n do
r r with its U NDO -N EXT -LSN, if any, replaced with the mapped LSN
if r is other than a buffering-specific log record then
log .n 0 ;r/
insert .n; n 0 / to the primary-to-backup LSN mapping
if r describes updates on some pages then
for each updated-page page-id p in r do
append the log record r with LSN n 0 to work queue h.p/
end for
else if r is a transaction-control-action log record for transaction T then
if r is a commit-transaction log record then
flush-the-log ./
remove the record of T from the active-transaction table
else {r is a begin-transaction, abort-transaction, set-savepoint, rollback-to-savepoint or
complete-rollback-to-savepoint log record}
update the record of T in the active-transaction table
end if
end if
end if
r the next log record from the primary system
end while
Algorithm 13.9 Processing work queue w
r the first record on work queue w
while r is a log record with backup-LSN n do
W ORK -Q UEUE -R EC -LSN. w / n
if r describes updates on pages p 1 ;:::;p k then
for all i D 1;:::;k do
if h.p i / D w and R EC -LSN.p i / n then
fix-and-write-latch .p i /
if page p i is unmodified then
R EC -LSN.p i / P AGE -LSN.p i /C1
end if
if P AGE -LSN.p i /<n then
apply the update described by r on page p i
P AGE -LSN.p i / n
end if
unlatch-and-unfix .p i /
end if
end for
end if
remove r from work queue w
r the first record on work queue w
end while