UNDO / REDO (Case Security and Recovery Database)

there are tree tables.

master_stock(stockcode {pk}, name, qty, sprice, bprice);

master_tran(trannum {pk}, trdate, note);

master_list(trannum {pk}, stockcode {fk}, qty, sprice);

TRANNUM field in the table used as MASTER_TRAN code transactions that occur in accordance with the date and serial transaction example: 20081014001, 20081014002 ... etc. (charging TRANNUM so here are affected in date of the occurrence of the transaction, the transaction serial number on the day)

(parent transaction information)

master_list while the table is used to record details transactions that occur in accordance with the transaction number (TRANNUM) MASTER_TRAN on the table.

Logically:

- A number based on the transaction MASTER_TRAN table (take appropriate filter records last date) then add the number 1) example: if the last record is 20081014050 (OLD), so that a new course record 20081014051 (NEW).

- And write new data MASTER_LIST based on the code.

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The process in computer A

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T1: create a number of Transaction (completed / commit) time required T1, T2, T3 (the number is obtained 20081014050)

T2: record list of goods, the time needed T4, T5, t6, t7, t8, T9, t10, t11, t12, t13, t14

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The Proces in computer B

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T1: create a transaction number (completed / commit) time needed T4, T5, t6 (a number that is obtained 20081014051)

T2: record list of goods, the time needed is t7, t8 (commit)

From the two processes occur if the computer T_crashes or T_checkpoint in t9 time which must UNDO and Redo?