TRANSACTION TAPES: SYSTEM SEQUENCE NUMBERS

The system sequencing information consists of four (4) sequence numbers. All four numbers are written to the

beginning of file-save, update save and transaction tapes.

The File Restore software checks the sequencing information to see if the tapes are loaded in the proper order. An error message is displayed if the sequence is out of order.

(However, the operator is given an option to override the sequence check.)

The first three sequence numbers (Full file-save, Reset option, and Update save sequence numbers) are explained in section 3.4, UPDATE SAVE PROCEDURES, and are not covered in this section. The fourth sequence number is explained below.

Transaction Sequence Number

The transaction sequence number is the total number of transaction logging sessions since the last file save or

update save. Whenever the transaction logger is activated or restarted, the transaction sequence number is incremented by one. The transaction sequence number is reset to zero by the SAVE command if the save is either a full file-save or an update save.

Format of Sequencing Information on Tape

The transaction logger writes a sequencing information segment on a transaction tape at the beginning of a

transaction logging session. The segment is similar to that written on file save or update save tapes. But, a second set of the four sequence numbers may also be appended to the segment. The second set of sequence numbers, if present, is called the continuation sequencing information.

continuation sequencing information I

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where:

v =

signifies the beginning of sequencing information x

=

(1 digit hex number) "0" if a file-save,

update-save, or transaction tape; or "1" if an account-save tape.

s

=

f

=

r =

u =

(4 digit hex number) system revision number (currently always 0001).

(4 digit hex number) full file-save sequence number, or 0000 for account-save tapes.

(4 digit hex number) R-option sequence number, or 0000 for account~save tapes.

(4 digit hex number) update-save sequence number, or 0000 for account-save tapes.

t

=

(4 digit hex number) transaction sequence number, or 0000 for file-save and account-save tapes.

*

⁼ asterisk; if present, is used to separate the two sets of sequence numbers.

A

=

attribute mark.

=

segment mark.

At the end of a full file-save, the file-save sequence number (f) is incremented by one (1) and the transaction sequence number (t) is reset to zero. This signifies that a full file-save has completed and this file-save tape is the

"reference" file-save tape of all subsequent transaction tapes.

When the transaction logger is deactivated or suspended, the logger terminates the current transaction tape by writing an End of File (BOF) mark to the tape. This signifies the end of a transaction logging session.

From the Transaction Logger menu, the Logger may be:

1. Re-activated after deactivation by using Option 1.

2. Restarted after suspension by using Option 4.

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Both actions start a new transaction logging session.

However, there is a difference between the two:

1. After the Logger is deactivated (i.e., exited) by Option 2 of the Transaction Logger menu, updates are no longer recorded as transactions. When i t is re-activated, some updates to the files may have taken place but are not logged. The new

(re-activated) transaction logging session is not a

"logical continuation" of the last session because there is a "gap" between the two.

2. After the Logger is suspended by Option 3 of the Transaction Logger menu, the Logger is still active and transactions are still recorded on the disk queue. When the tape is restarted, transactions recorded on disk during the period of suspension are dumped onto tape. The new (restarted)

transaction logging session is a logical

continuation of the last session because there is no "gap" between the two.

The continuation sequencing information is used to mark the transaction tapes in such a way that the above two situations can be distinguished:

When the logger is re-activated or restarted, the logger increments the transaction sequence number by one (1), and then writes the sequencing information segment to the

beginning of the new transaction tape. The segment always contains the sequencing information of the current

transaction logging session.

NOTE: In the case of re-activation, no continuation

sequencing information is written in the sequencing information segment (i.e., the asterisk and the last four numbers are not included in the

sequencing information segment).

In the case of restart, continuation sequencing information is included in the sequencing

information segment. The continuation sequencing information is the sequencing information of the last transaction logging session.

Figure A illustrates an example of how the sequencing information is updated for transaction logging.

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EXAMPLE OF SEQUENCING INFORMATION IN TRANSACTION TAPES

file-save, R-option, Update save and Transaction sequence numbers). Note that the sequencing

information segment on a transaction tape may contain two sets of numbers, separated by an

as~erisk. The first set of number is the sequencing information of the current transaction logging

session. The second set, if present, is the

System Management Page 144 Backup/Restore

Notes on Sequencing Information (continued) NOTE 4:

NOTE 5:

NOTE 6:

NOTE 7:

The first two transaction tape sets (seq#=l 1 0 1 and 1 1 0 2) are associated with the first (Friday evening) FILE-SAVE tape (seq#=l 1 0 0). The last three transaction tape sets (seq#=2 2 0 1, 2 2 0 2 and 2 2 0 3) are associated with the Wednesday evening FILE-SAVE tape (seq#=2 2 0 0).

All transaction tape sets, except the last one (2 2

o

3), are logical continuations of the previous tapes.

On the second Friday, the logger was deactivated between lOam and 1pm. When the logger was

re-activated at 1pm, the transaction tape set (seq#=2 2 0 3) did not have the continuation sequencing information. This signifies that some transactions were not recorded by the transaction logger during this "deactivation period". If, for example, a user created a file during the

deactivation period, this transaction was not logged and data may be lost. For more information on data loss, see also section "ERROR CONDITIONS WITH TRANSACTION TAPES".

Transaction tape set 2 2 0 1 is associated with FILE-SAVE tape 2 2 0 O. At the same time, this tape is also a logical continuation of 1 1 0 2. This means that the .user could full-restore the system with anyone of the following two restore

sequences:

normal restore sequence "long" restore sequence

---

---Load FILE-SAVE tape 2 2 0 0 Load FILE-SAVE tape 1 1 0 0 Load Trans. tape 2 2 0 1 Load Trans. tape 1 1 0 1 Load Trans. tape 2 2 0 2 Load Trans. tape 1 1 0 2 Load Trans. tape 2 2 0 3 Load Trans. tape 2 2 0 1 Load Tram'i. tape 2 2 0 2 Load Trans. tape 2 2 0 3 Figure A (cont.) Transaction Tape Sequencing Information

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3.5.4 CONSIDERATIONS BEFORE USING THE TRANSACTION LOGGER

Im Dokument File virtual File (Seite 142-147)