/**
* Fast check to see if a shard has messages to process
*
* @param shardName
* @throws MessageQueueException
*/
private boolean hasMessages(String shardName) throws MessageQueueException {
UUID currentTime = TimeUUIDUtils.getUniqueTimeUUIDinMicros();
try {
ColumnList<MessageQueueEntry> result =
keyspace
.prepareQuery(queueColumnFamily)
.setConsistencyLevel(consistencyLevel)
.getKey(shardName)
.withColumnRange(
new RangeBuilder()
.setLimit(1) // Read extra messages because of the lock column
.setStart(
entrySerializer
.makeEndpoint(
(byte) MessageQueueEntryType.Message.ordinal(), Equality.EQUAL)
.toBytes())
.setEnd(
entrySerializer
.makeEndpoint(
(byte) MessageQueueEntryType.Message.ordinal(), Equality.EQUAL)
.append((byte) 0, Equality.EQUAL)
.append(currentTime, Equality.LESS_THAN_EQUALS)
.toBytes())
.build())
.execute()
.getResult();
return !result.isEmpty();
} catch (ConnectionException e) {
throw new MessageQueueException("Error checking shard for messages. " + shardName, e);
}
}
/**
* Peek into messages contained in the shard. This call does not take trigger time into account
* and will return messages that are not yet due to be executed
*
* @param shardName
* @param itemsToPop
* @return
* @throws MessageQueueException
*/
private Collection<Message> peekMessages(String shardName, int itemsToPeek)
throws MessageQueueException {
try {
ColumnList<MessageQueueEntry> result =
keyspace
.prepareQuery(queueColumnFamily)
.setConsistencyLevel(consistencyLevel)
.getKey(shardName)
.withColumnRange(
new RangeBuilder()
.setLimit(itemsToPeek)
.setStart(
entrySerializer
.makeEndpoint(
(byte) MessageQueueEntryType.Message.ordinal(),
Equality.GREATER_THAN_EQUALS)
.toBytes())
.setEnd(
entrySerializer
.makeEndpoint(
(byte) MessageQueueEntryType.Message.ordinal(),
Equality.LESS_THAN_EQUALS)
.toBytes())
.build())
.execute()
.getResult();
List<Message> messages = Lists.newArrayListWithCapacity(result.size());
for (Column<MessageQueueEntry> column : result) {
Message message = extractMessageFromColumn(column);
if (message != null) messages.add(message);
}
return messages;
} catch (ConnectionException e) {
throw new MessageQueueException("Error peeking for messages from shard " + shardName, e);
}
}