IBM 000-8697 Manual de usuario descargar pdf (Pagina 671)

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Product Environment 9-51

Determining Database Consistency

Thissection describes the administrativeprocedurethatmight be requiredif

a database server process or transaction is killed after it has entered the

second phase of the two-phase commit protocol. You must perform this

procedure if one of the following two scenarios has occurred:

■ A heuristic decision to roll back occurred at a participant OnLine

after the coordinator received an acknowledgment from this partic-

ipant that it was able to commit and the coordinator later instructed

all participants to commit.

■ You,asadministrator,executedthetbmode-Z optionataparticipant

OnLine to initiate a heuristic end-transaction after this participant

sent an acknowledgment that it was able to commit.

Under normal processing, the need to perform this determination should

occur rarely, if at all.

Administrators are strongly advised to avoid this situation. Do not kill a

databaseserverprocessortransactionafterit has enteredthesecond phase of thetwo-

phase commit protocol unless it is absolutely necessary.

There are ﬁve steps to determine database consistency and correct the

situation, if required:

1. Determine which participating OnLine database servers committed

a heuristic decision.

2. Determine if the networked database system contains inconsistent

data.

3. Decide if action to correct the situation is required.

4. Decide if you need to roll back the transaction where it committed,

or recommit the transaction where it rolled back.

5. Implement the decision manually through inspection of the logical

logs at each affected OnLine.

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