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;
}
private RecordId getRecordId(int lineNo) throws IOException {
RecordId id = null;
Jedis jedis = pool_.getResource();
try {
int pageNo, slotNo;
String lineNoStr = Integer.toString(lineNo);
String pageNoStr = jedis.hget(lineNoStr, PAGE_NO_KEY);
String slotNoStr = jedis.hget(lineNoStr, SLOT_NO_KEY);
if (pageNoStr != null && slotNoStr != null) {
id = new RecordId(Integer.parseInt(pageNoStr), Integer.parseInt(slotNoStr));
} else { // Was not cached
// Read directory page containing line in question
byte[] buffer = new byte[BLOCK_SIZE];
int absIndex = (lineNo - 1) * 2 * INT_SIZE;
int relativeIndex = absIndex % BLOCK_SIZE;
int bytesRead = 0;
synchronized (mDirectoryFile) {
mDirectoryFile.seek(absIndex - relativeIndex);
bytesRead = mDirectoryFile.read(buffer);
}
ByteBuffer bb = ByteBuffer.wrap(buffer);
// Cache all entries in the page
int curLineNo = lineNo - relativeIndex / (2 * INT_SIZE);
for (int i = 0; i < bytesRead / (2 * INT_SIZE); i++, curLineNo++) {
pageNo = bb.getInt();
slotNo = bb.getInt();
if (curLineNo == lineNo) {
id = new RecordId(pageNo, slotNo);
}
lineNoStr = Integer.toString(curLineNo);
jedis.hset(lineNoStr, PAGE_NO_KEY, Integer.toString(pageNo));
jedis.hset(lineNoStr, SLOT_NO_KEY, Integer.toString(slotNo));
}
}
if (id == null) {
throw new IOException("LineServer: Could not find record id in directory");
}
} finally {
pool_.returnResource(jedis);
}
return id;
}
