public String getLine(int lineNo) throws Exception {
if (lineNo <= 0 || lineNo > mNumLines) {
return null;
}
String line = null;
Jedis jedis = pool_.getResource();
try {
String lineNoStr = Integer.toString(lineNo);
line = jedis.hget(lineNoStr, LINE_KEY);
if (line == null) {
RecordId lineId = getRecordId(lineNo);
byte[] buffer = new byte[BLOCK_SIZE];
synchronized (mDataFile) {
mDataFile.seek(lineId.pageNo() * BLOCK_SIZE);
mDataFile.read(buffer);
}
ByteBuffer bb = ByteBuffer.wrap(buffer);
int numRecords = bb.getInt(BLOCK_SIZE - INT_SIZE);
int indexPos = BLOCK_SIZE - 3 * INT_SIZE;
int curLineNo = lineNo - lineId.slotNo() + 1;
String[] recordKeys = {PAGE_NO_KEY, SLOT_NO_KEY};
for (int i = 1; i < numRecords; i++, curLineNo++) {
int offset = bb.getInt(indexPos);
int len = bb.getInt(indexPos + INT_SIZE);
ByteBuffer linebb = ByteBuffer.wrap(buffer, offset, len);
byte[] lineBuf = new byte[linebb.remaining()];
linebb.get(lineBuf);
String lineStr = new String(lineBuf);
if (i == lineId.slotNo()) {
line = lineStr;
}
// Store in cache
lineNoStr = Integer.toString(curLineNo);
jedis.hdel(lineNoStr, recordKeys);
jedis.hset(lineNoStr, LINE_KEY, lineStr);
indexPos -= 2 * INT_SIZE;
}
}
if (line == null) {
throw new Exception("LineServer: Could not find line on page");
}
} catch (IOException ioe) {
System.err.println("LineServer: IOException on line retrieval");
throw ioe;
} finally {
pool_.returnResource(jedis);
}
return line;
}
/**
* Delete the specified tuple from the page; the tuple should be updated to reflect that it is no
* longer stored on any page.
*
* @throws DbException if this tuple is not on this page, or tuple slot is already empty.
* @param t The tuple to delete
*/
public void deleteTuple(Tuple t) throws DbException {
// some code goes here
// not necessary for lab1
RecordId targetrid = t.getRecordId();
int tslotnum = targetrid.tupleno();
if (!targetrid.getPageId().equals(pid) || !isSlotUsed(tslotnum)) {
throw new DbException("Either wrong page number or requested tuple didn't exist");
}
markSlotUsed(tslotnum, false);
tuples[tslotnum] = null;
}
// see DbFile.java for javadocs
public Page deleteTuple(TransactionId tid, Tuple t)
throws DbException, TransactionAbortedException {
// some code goes here
BufferPool bp = Database.getBufferPool();
RecordId rid = t.getRecordId();
if (rid == null) {
throw new DbException("Tuple is not a member of this file");
}
HeapPage p = (HeapPage) bp.getPage(tid, rid.getPageId(), Permissions.READ_WRITE);
p.deleteTuple(t);
return p;
}