org.apache.hadoop.hbase.regionserver
Class RegionMergeTransaction

java.lang.Object
  org.apache.hadoop.hbase.regionserver.RegionMergeTransaction

@InterfaceAudience.Private
public class RegionMergeTransaction
extends Object

Executes region merge as a "transaction". It is similar with SplitTransaction. Call prepare(RegionServerServices) to setup the transaction, execute(Server, RegionServerServices) to run the transaction and rollback(Server, RegionServerServices) to cleanup if execute fails.

Here is an example of how you would use this class:

  RegionMergeTransaction mt = new RegionMergeTransaction(this.conf, parent, midKey)
  if (!mt.prepare(services)) return;
  try {
    mt.execute(server, services);
  } catch (IOException ioe) {
    try {
      mt.rollback(server, services);
      return;
    } catch (RuntimeException e) {
      myAbortable.abort("Failed merge, abort");
    }
  }
 

This class is not thread safe. Caller needs ensure merge is run by one thread only.

Constructor Summary

RegionMergeTransaction(HRegion a, HRegion b, boolean forcible)
Constructor

Method Summary

static void	createNodeMerging(ZooKeeperWatcher zkw, HRegionInfo region, ServerName serverName, HRegionInfo a, HRegionInfo b) Creates a new ephemeral node in the PENDING_MERGE state for the merged region.
HRegion	execute(Server server, RegionServerServices services) Run the transaction.
static HRegionInfo	getMergedRegionInfo(HRegionInfo a, HRegionInfo b) Get merged region info through the specified two regions
boolean	prepare(RegionServerServices services) Does checks on merge inputs.
boolean	rollback(Server server, RegionServerServices services)
static int	transitionMergingNode(ZooKeeperWatcher zkw, HRegionInfo merged, HRegionInfo a, HRegionInfo b, ServerName serverName, int znodeVersion, EventType beginState, EventType endState) Transitions an existing ephemeral node for the specified region which is currently in the begin state to be in the end state.

Methods inherited from class java.lang.Object

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

Constructor Detail

RegionMergeTransaction

public RegionMergeTransaction(HRegion a,
                              HRegion b,
                              boolean forcible)

Constructor

Parameters:

a - region a to merge

b - region b to merge

forcible - if false, we will only merge adjacent regions

Method Detail

prepare

public boolean prepare(RegionServerServices services)

Does checks on merge inputs.

Parameters:

services -

Returns:

true if the regions are mergeable else false if they are not (e.g. its already closed, etc.).

execute

public HRegion execute(Server server,
                       RegionServerServices services)
                throws IOException

Run the transaction.

Parameters:

server - Hosting server instance. Can be null when testing (won't try and update in zk if a null server)

services - Used to online/offline regions.

Returns:

merged region

Throws:

IOException - If thrown, transaction failed. Call rollback(Server, RegionServerServices)

IOException

See Also:

rollback(Server, RegionServerServices)

getMergedRegionInfo

public static HRegionInfo getMergedRegionInfo(HRegionInfo a,
                                              HRegionInfo b)

Get merged region info through the specified two regions

Parameters:

a - merging region A

b - merging region B

Returns:

the merged region info

rollback

public boolean rollback(Server server,
                        RegionServerServices services)
                 throws IOException

Parameters:

server - Hosting server instance (May be null when testing).

services - Services of regionserver, used to online regions.

Returns:

True if we successfully rolled back, false if we got to the point of no return and so now need to abort the server to minimize damage.

Throws:

IOException - If thrown, rollback failed. Take drastic action.

createNodeMerging

public static void createNodeMerging(ZooKeeperWatcher zkw,
                                     HRegionInfo region,
                                     ServerName serverName,
                                     HRegionInfo a,
                                     HRegionInfo b)
                              throws org.apache.zookeeper.KeeperException,
                                     IOException

Creates a new ephemeral node in the PENDING_MERGE state for the merged region. Create it ephemeral in case regionserver dies mid-merge.

Does not transition nodes from other states. If a node already exists for this region, a KeeperException.NodeExistsException will be thrown.

Parameters:

zkw - zk reference

region - region to be created as offline

serverName - server event originates from

Throws:

org.apache.zookeeper.KeeperException

IOException

transitionMergingNode

public static int transitionMergingNode(ZooKeeperWatcher zkw,
                                        HRegionInfo merged,
                                        HRegionInfo a,
                                        HRegionInfo b,
                                        ServerName serverName,
                                        int znodeVersion,
                                        EventType beginState,
                                        EventType endState)
                                 throws org.apache.zookeeper.KeeperException,
                                        IOException

Transitions an existing ephemeral node for the specified region which is currently in the begin state to be in the end state. Master cleans up the final MERGE znode when it reads it (or if we crash, zk will clean it up).

Does not transition nodes from other states. If for some reason the node could not be transitioned, the method returns -1. If the transition is successful, the version of the node after transition is returned.

This method can fail and return false for three different reasons:

• Node for this region does not exist
• Node for this region is not in the begin state
• After verifying the begin state, update fails because of wrong version (this should never actually happen since an RS only does this transition following a transition to the begin state. If two RS are conflicting, one would fail the original transition to the begin state and not this transition)

Does not set any watches.

This method should only be used by a RegionServer when merging two regions.

Parameters:

zkw - zk reference

merged - region to be transitioned to opened

a - merging region A

b - merging region B

serverName - server event originates from

znodeVersion - expected version of data before modification

beginState - the expected current state the znode should be

endState - the state to be transition to

Returns:

version of node after transition, -1 if unsuccessful transition

Throws:

org.apache.zookeeper.KeeperException - if unexpected zookeeper exception

IOException