IBM 000-8697 Bedienungsanleitung PDF herunterladen (Seite 657)

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Product Environment 9-37

Heuristic Rollback

It is important to recognize that this rollback does not close the transaction as it

wouldinasingleOnLineenvironment.Undertwo-phasecommit,thelogicallog

ﬁles that contain records associated with the piece of work are considered

open until an ENDTRANS logical log record is written.(Referto page 9-44 for

more details about the logical log records during the two-phase commit

protocol.)

It is quite possible that the logical log will continue to ﬁll until the exclusive

high-water mark is reached (LTXEHWM). If this happens, alldatabase server

processes are suspended except those that are currently rolling back or

currently committing. In the two-phase commit scenario, the open trans-

actionpreventsyou frombacking up thelogicallog ﬁles andfreeing space in

the logical log. Under these speciﬁc circumstances, the logical log can ﬁll

completely.Ifthishappens,OnLineshutsdownandyoumustperformadata

restore.

Condition 2: You Execute tbmode -z

You, as administrator, can decide to initiate a heuristic rollback of a precom-

mitted piece of work by executing tbmode -z. You might make this decision

because you want to free the resources that are held by the piece of work. (If

youkillthedatabaseserverprocessbyexecutingtbmode-z,youfreealllocks

and shared-memory resources that are held by the database server process

even though you do not end the transaction.) The likely consequence of this

action isthat the coordinator willeventually contact the participant, learnof

the heuristic rollback, and direct the participant to end the transaction

without an interruptioninprocessing.However, youarestronglyadvised to

considertheother,lesslikelyconsequence(manualrecovery)beforeyoutake

this action.

When a Heuristic Rollback Occurs

When a heuristic rollback occurs at a participant OnLine, a record is placed

in the OnLine logical log (type HEURTX) where the rollback occurred. Locks

and resources held by the transaction are freed. The tbinit daemon writes a

message in the OnLine message log indicating that a long-transaction

condition and rollback occurred. (Refer to page 8-29 for a complete

description of the message.)

Transaction Completed Abnormally (rollback):

tx=address flags=0xnn

1 2 ... 652 653 654 655 656 657 658 659 660 661 662 ... 701 702

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