private void populateRowCache(Set<byte[]> excludeRows, int maxBatchSize) throws IOException {
long readPointer = transaction.getReadPointer();
// Scan the table for queue entries.
int numRows = Math.max(MIN_FETCH_ROWS, maxBatchSize * PREFETCH_BATCHES);
if (scanStartRow == null) {
scanStartRow = Arrays.copyOf(startRow, startRow.length);
}
QueueScanner scanner =
getScanner(
scanStartRow,
QueueEntryRow.getStopRowForTransaction(queueRowPrefix, transaction),
numRows);
try {
// Try fill up the cache
boolean firstScannedRow = true;
while (entryCache.size() < numRows) {
ImmutablePair<byte[], Map<byte[], byte[]>> entry = scanner.next();
if (entry == null) {
// No more result, breaking out.
break;
}
byte[] rowKey = entry.getFirst();
if (excludeRows.contains(rowKey)) {
continue;
}
// Row key is queue_name + writePointer + counter
long writePointer = Bytes.toLong(rowKey, queueRowPrefix.length, Longs.BYTES);
// If it is first row returned by the scanner and was written before the earliest in
// progress,
// it's safe to advance scanStartRow to current row because nothing can be written before
// this row.
if (firstScannedRow && writePointer < transaction.getFirstInProgress()) {
firstScannedRow = false;
scanStartRow = Arrays.copyOf(rowKey, rowKey.length);
}
// If writes later than the reader pointer, abort the loop, as entries that comes later are
// all uncommitted.
// this is probably not needed due to the limit of the scan to the stop row, but to be
// safe...
if (writePointer > readPointer) {
break;
}
// If the write is in the excluded list, ignore it.
if (transaction.isExcluded(writePointer)) {
continue;
}
// Based on the strategy to determine if include the given entry or not.
byte[] dataBytes = entry.getSecond().get(QueueEntryRow.DATA_COLUMN);
byte[] metaBytes = entry.getSecond().get(QueueEntryRow.META_COLUMN);
if (dataBytes == null || metaBytes == null) {
continue;
}
byte[] stateBytes = entry.getSecond().get(stateColumnName);
int counter = Bytes.toInt(rowKey, rowKey.length - 4, Ints.BYTES);
if (!shouldInclude(writePointer, counter, metaBytes, stateBytes)) {
continue;
}
entryCache.put(rowKey, new SimpleQueueEntry(rowKey, dataBytes, stateBytes));
}
} finally {
scanner.close();
}
}
