Question

Explain why the Transaction class method nextTxNumber is synchronized.

1) What could happen if it were not?

2) Is it a problem for the other methods in that class to not be synchronized?

Please explain your answer.

public int size(String filename) { Block dummyblknew Block(filename, END_OF_FILE); concurMgr.sLock (dummyblk); return SimpleDB.fileMgr).size(filename); Appends a new block to the end of the specified file and returns a reference to it. *This method first obtains an XLock on the "end of the file", before performing the append Oparam filename the name of the file param fmtr the formatter used to initialize the new page * return a reference to the newly-created disk block public Block append(String filename, PageFormatter fmtr) Block dummyblknew Block(filename, END_OF_FILE); concurMgr.xLock (dummyblk); Block blk myBuffers.pinNew(filename, fmtr); unpin(blk); return blk; private static synchronized int nextTxNumber){ nextTxNum++; System.out.println("new transaction:"nextTxNum); return next TxNum

Answer 1

Answer 1:
It is synchronized because it is returning a sequence number so it should be unique so
that is the reason we are not allowing 2 threads to access that method at time
If we remove at some times 2 threads might execute at time both threads will get the same number

Answer 2:
It is not a problem because those methods will not cause the data inconsistency

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