org.apache.accumulo.server.master.balancer

Class GroupBalancer

java.lang.Object

org.apache.accumulo.server.master.balancer.TabletBalancer

org.apache.accumulo.server.master.balancer.GroupBalancer

Direct Known Subclasses:

RegexGroupBalancer

public abstract class GroupBalancer
extends TabletBalancer

A balancer that evenly spreads groups of tablets across all tablet server. This balancer accomplishes the following two goals :

• Evenly spreads each group across all tservers.
• Minimizes the total number of groups on each tserver.

To use this balancer you must extend it and implement getPartitioner(). See RegexGroupBalancer as an example.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	GroupBalancer.Location

Nested classes/interfaces inherited from class org.apache.accumulo.server.master.balancer.TabletBalancer

TabletBalancer.BalancerProblem, TabletBalancer.NoTservers, TabletBalancer.OutstandingMigrations

Field Summary

Fields inherited from class org.apache.accumulo.server.master.balancer.TabletBalancer

configuration, context, TIME_BETWEEN_BALANCER_WARNINGS

Constructor Summary

Constructors

Constructor and Description
GroupBalancer(String tableId)

Method Summary

Methods

Modifier and Type	Method and Description
long	balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut) Ask the balancer if any migrations are necessary.
void	getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned, Map<KeyExtent,TServerInstance> assignments) Assign tablets to tablet servers.
protected Iterable<Pair<KeyExtent,GroupBalancer.Location>>	getLocationProvider()
protected int	getMaxMigrations() The maximum number of migrations to perform in a single pass.
protected abstract com.google.common.base.Function<KeyExtent,String>	getPartitioner()
protected long	getWaitTime() The amount of time to wait between balancing.
protected boolean	shouldBalance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations)

Methods inherited from class org.apache.accumulo.server.master.balancer.TabletBalancer

checkMigrationSanity, constraintNotMet, getOnlineTabletsForTable, init, init, resetBalancerErrors

Methods inherited from class java.lang.Object

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

Constructor Detail

GroupBalancer

public GroupBalancer(String tableId)

Method Detail

getPartitioner

protected abstract com.google.common.base.Function<KeyExtent,String> getPartitioner()

Returns:

A function that groups tablets into named groups.

getLocationProvider

protected Iterable<Pair<KeyExtent,GroupBalancer.Location>> getLocationProvider()

getWaitTime

protected long getWaitTime()

The amount of time to wait between balancing.

getMaxMigrations

protected int getMaxMigrations()

The maximum number of migrations to perform in a single pass.

shouldBalance

protected boolean shouldBalance(SortedMap<TServerInstance,TabletServerStatus> current,
                    Set<KeyExtent> migrations)

Returns:

Examine current tserver and migrations and return true if balancing should occur.

getAssignments

public void getAssignments(SortedMap<TServerInstance,TabletServerStatus> current,
                  Map<KeyExtent,TServerInstance> unassigned,
                  Map<KeyExtent,TServerInstance> assignments)

Description copied from class: TabletBalancer

Assign tablets to tablet servers. This method is called whenever the master finds tablets that are unassigned.

Specified by:

getAssignments in class TabletBalancer

Parameters:

current - The current table-summary state of all the online tablet servers. Read-only. The TabletServerStatus for each server may be null if the tablet server has not yet responded to a recent request for status.

unassigned - A map from unassigned tablet to the last known tablet server. Read-only.

assignments - A map from tablet to assigned server. Write-only.

balance

public long balance(SortedMap<TServerInstance,TabletServerStatus> current,
           Set<KeyExtent> migrations,
           List<TabletMigration> migrationsOut)

Description copied from class: TabletBalancer

Ask the balancer if any migrations are necessary. If the balancer is going to self-abort due to some environmental constraint (e.g. it requires some minimum number of tservers, or a maximum number of outstanding migrations), it should issue a log message to alert operators. The message should be at WARN normally and at ERROR if the balancer knows that the problem can not self correct. It should not issue these messages more than once a minute.

Specified by:

balance in class TabletBalancer

Parameters:

current - The current table-summary state of all the online tablet servers. Read-only.

migrations - the current set of migrations. Read-only.

migrationsOut - new migrations to perform; should not contain tablets in the current set of migrations. Write-only.

Returns:

the time, in milliseconds, to wait before re-balancing. This method will not be called when there are unassigned tablets.