Package org.apache.accumulo.core.spi.scan

Interface ScanServerSelector

All Known Implementing Classes:

ConfigurableScanServerHostSelector, ConfigurableScanServerSelector

public interface ScanServerSelector

A client side plugin that determines what scan servers to use for eventually consistent scans. When a scanner sets ScannerBase.setConsistencyLevel(ScannerBase.ConsistencyLevel) to ScannerBase.ConsistencyLevel.EVENTUAL then this plugin is used to determine which scan servers to use for a given tablet. To configure a class to use for this plugin, set its name using the client config scan.server.selector.impl

Since:

2.1.0

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	ScanServerSelector.InitParameters	This interface exists so that is easier to evolve what is passed to init(InitParameters) without having to make breaking changes.
static interface	ScanServerSelector.SelectorParameters	This interface exists so that is easier to evolve what is passed to selectServers(SelectorParameters) without having to make breaking changes.

Field Summary

Fields

Modifier and Type	Field	Description
static final String	DEFAULT_SCAN_SERVER_GROUP_NAME	The scan server group name that will be used when one is not specified.

Method Summary

Modifier and Type	Method	Description
default void	init(ScanServerSelector.InitParameters params)	This method is called once after a ScanServerSelector is instantiated.
ScanServerSelections	selectServers(ScanServerSelector.SelectorParameters params)	Uses the ScanServerSelector.SelectorParameters to determine which, if any, ScanServer should be used for scanning a tablet.

Field Details

DEFAULT_SCAN_SERVER_GROUP_NAME

static final String DEFAULT_SCAN_SERVER_GROUP_NAME

The scan server group name that will be used when one is not specified.

See Also:

• Constant Field Values

Method Details

init

default void init(ScanServerSelector.InitParameters params)

This method is called once after a ScanServerSelector is instantiated.

selectServers

ScanServerSelections selectServers(ScanServerSelector.SelectorParameters params)

Uses the ScanServerSelector.SelectorParameters to determine which, if any, ScanServer should be used for scanning a tablet.

In the case where there are zero scan servers available and an implementation does not want to fall back to tablet servers, its ok to wait and poll for scan servers. When waiting its best to use ScanServerSelector.SelectorParameters.waitUntil(Supplier, Duration, String) as this allows Accumulo to know about the wait and cancel it via exceptions when it no longer makes sense to wait.

Parameters:

params - parameters for the calculation

Returns:

results