To draw a presedence graph, you first draw three circles, one for each transaction. Next, you go through the schedule, drawing a line from Transaction A to Transaction B whenever;
- B reads an attribute which A has written to at a previous time
- B write an attribute which A has written to at a previous time
- B writes an attribute which A has read from at a previous time
The connection from Transaction 2 to 1 involving B, and from 3 to 1 involving B do not fall into any of these three categories.
To draw a presedence graph, you first draw three circles, one for each transaction. Next, you go through the schedule, drawing a line from Transaction A to Transaction B whenever;
- B reads an attribute which A has written to at a previous time
- B write an attribute which A has written to at a previous time
- B writes an attribute which A has read from at a previous time
The graph shown has something missing.
To draw a presedence graph, you first draw three circles, one for each transaction. Next, you go through the schedule, drawing a line from Transaction A to Transaction B whenever;
- B reads an attribute which A has written to at a previous time
- B write an attribute which A has written to at a previous time
- B writes an attribute which A has read from at a previous time
All the connections in this graph point the wrong way...
To draw a presedence graph, you first draw three circles, one for each transaction. Next, you go through the schedule, drawing a line from Transaction A to Transaction B whenever;
- B reads an attribute which A has written to at a previous time
- B write an attribute which A has written to at a previous time
- B writes an attribute which A has read from at a previous time
The connection from Transaction 2 to 1 involving B, and from 3 to 1 involving B do not fall into any of these three categories. In addition, the remaining connections in this graph involve the correct attributes and transactions but point the wrong way...
To draw a presedence graph, you first draw three circles, one for each transaction. Next, you go through the schedule, drawing a line from Transaction A to Transaction B whenever;
- B reads an attribute which A has written to at a previous time
- B write an attribute which A has written to at a previous time
- B writes an attribute which A has read from at a previous time
Well done.
Given the following transaction schedule:
| time | TRANSACTION 1 | TRANSACTION 2 | TRANSACTION 3 |
|---|---|---|---|
| t1 | read(A) | ||
| t2 | read(B) | read(B) | |
| t3 | read(B) | ||
| t4 | write(C) | ||
| t5 | write(B) | ||
| t6 | read(A) | ||
| t7 | write(A) | ||
| t8 | write(A) | ||
| t9 | write(C) |
- None of the above.
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