org.apache.cassandra.db
Class HintedHandOffManager

java.lang.Object
  org.apache.cassandra.db.HintedHandOffManager

public class HintedHandOffManager
extends java.lang.Object

For each table (keyspace), there is a row in the system hints CF. SuperColumns in that row are keys for which we have hinted data. Subcolumns names within that supercolumn are host IPs. Subcolumn values are always empty. Instead, we store the row data "normally" in the application table it belongs in. So when we deliver hints we look up endpoints that need data delivered on a per-key basis, then read that entire row out and send it over. (TODO handle rows that have incrementally grown too large for a single message.) HHM never deletes the row from Application tables; there is no way to distinguish that from hinted tombstones! instead, rely on cleanup compactions to remove data that doesn't belong on this node. (Cleanup compactions may be started manually -- on a per node basis -- with "nodeprobe cleanup.") TODO this avoids our hint rows from growing excessively large by offloading the message data into application tables. But, this means that cleanup compactions will nuke HH data. Probably better would be to store the RowMutation messages in a HHData (non-super) CF, modifying the above to store a UUID value in the HH subcolumn value, which we use as a key to a [standard] HHData system CF that would contain the message bytes. There are two ways hinted data gets delivered to the intended nodes. runHints() runs periodically and pushes the hinted data on this node to every intended node. runDelieverHints() is called when some other node starts up (potentially from a failure) and delivers the hinted data just to that node.

Field Summary

static java.lang.String	HINTS_CF
static HintedHandOffManager	instance

Constructor Summary

protected

HintedHandOffManager()

Method Summary

void	deliverHints(java.net.InetAddress to)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

instance

public static final HintedHandOffManager instance

HINTS_CF

public static final java.lang.String HINTS_CF

See Also:

Constant Field Values

Constructor Detail

HintedHandOffManager

protected HintedHandOffManager()

Method Detail

deliverHints

public void deliverHints(java.net.InetAddress to)