Package org.apache.accumulo.server.master.balancer

Class TabletBalancer

java.lang.Object

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

Direct Known Subclasses:

ChaoticLoadBalancer, DefaultLoadBalancer, GroupBalancer, TableLoadBalancer

public abstract class TabletBalancer
extends Object

This class is responsible for managing the distribution of tablets throughout an Accumulo cluster. In most cases, users will want a balancer implementation which ensures a uniform distribution of tablets, so that no individual tablet server is handling significantly more work than any other.

Implementations may wish to store configuration in Accumulo's system configuration using the Property.GENERAL_ARBITRARY_PROP_PREFIX. They may also benefit from using per-table configuration using Property.TABLE_ARBITRARY_PROP_PREFIX.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
protected static class	TabletBalancer.BalancerProblem	A deferred call descendent TabletBalancers use to log why they can't continue.
protected static class	TabletBalancer.NoTservers	If a TabletBalancer requires active tservers, it should use this problem to indicate when there are none.
protected static class	TabletBalancer.OutstandingMigrations	If a TabletBalancer only balances when there are no outstanding migrations, it should use this problem to indicate when they exist.

Field Summary

Fields

Modifier and Type	Field	Description
protected ServerContext	context
protected static long	TIME_BETWEEN_BALANCER_WARNINGS

Constructor Summary

Constructors

Constructor	Description
TabletBalancer()

Method Summary

Modifier and Type	Method	Description
abstract long	balance(SortedMap<TServerInstance,TabletServerStatus> current, Set<KeyExtent> migrations, List<TabletMigration> migrationsOut)	Ask the balancer if any migrations are necessary.
static List<TabletMigration>	checkMigrationSanity(Set<TServerInstance> current, List<TabletMigration> migrations)	Utility to ensure that the migrations from balance() are consistent: Tablet objects are not null Source and destination tablet servers are not null and current
protected void	constraintNotMet(TabletBalancer.BalancerProblem cause)	Warn that a Balancer can't work because of some external restriction.
abstract void	getAssignments(SortedMap<TServerInstance,TabletServerStatus> current, Map<KeyExtent,TServerInstance> unassigned, Map<KeyExtent,TServerInstance> assignments)	Assign tablets to tablet servers.
List<TabletStats>	getOnlineTabletsForTable(TServerInstance tserver, TableId tableId)	Fetch the tablets for the given table by asking the tablet server.
void	init(ServerConfigurationFactory conf)	Deprecated. since 2.0.0; use init(ServerContext) instead.
void	init(ServerContext context)	Initialize the TabletBalancer.
protected void	resetBalancerErrors()	Resets logging about problems meeting an external constraint on balancing.

Methods inherited from class java.lang.Object

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

Field Detail

context

protected ServerContext context

TIME_BETWEEN_BALANCER_WARNINGS

protected static final long TIME_BETWEEN_BALANCER_WARNINGS

See Also:

Constant Field Values

Constructor Detail

TabletBalancer

public TabletBalancer()

Method Detail

init

@Deprecated
public void init(ServerConfigurationFactory conf)

Deprecated.

since 2.0.0; use init(ServerContext) instead.

Initialize the TabletBalancer. This gives the balancer the opportunity to read the configuration.

init

public void init(ServerContext context)

Initialize the TabletBalancer. This gives the balancer the opportunity to read the configuration.

Since:

2.0.0

getAssignments

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

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

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

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.

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.

constraintNotMet

protected void constraintNotMet(TabletBalancer.BalancerProblem cause)

Warn that a Balancer can't work because of some external restriction. Will not call the provided logging handler more often than TIME_BETWEEN_BALANCER_WARNINGS

resetBalancerErrors

protected void resetBalancerErrors()

Resets logging about problems meeting an external constraint on balancing.

getOnlineTabletsForTable

public List<TabletStats> getOnlineTabletsForTable(TServerInstance tserver,
                                                  TableId tableId)
                                           throws ThriftSecurityException,
                                                  org.apache.thrift.TException

Fetch the tablets for the given table by asking the tablet server. Useful if your balance strategy needs details at the tablet level to decide what tablets to move.

Parameters:

tserver - The tablet server to ask.

tableId - The table id

Returns:

a list of tablet statistics

Throws:

ThriftSecurityException - tablet server disapproves of your internal System password.

org.apache.thrift.TException - any other problem

checkMigrationSanity

public static List<TabletMigration> checkMigrationSanity(Set<TServerInstance> current,
                                                         List<TabletMigration> migrations)

Utility to ensure that the migrations from balance() are consistent:

• Tablet objects are not null
• Source and destination tablet servers are not null and current

Returns:

A list of TabletMigration object that passed sanity checks.