org.apache.accumulo.tserver.compaction

Class CompactionStrategy

java.lang.Object

org.apache.accumulo.tserver.compaction.CompactionStrategy

Direct Known Subclasses:

ConfigurableCompactionStrategy, DefaultCompactionStrategy, EverythingCompactionStrategy

public abstract class CompactionStrategy
extends Object

The interface for customizing major compactions.

The tablet server has one thread to ask many tablets if they should compact. When the strategy returns true, then tablet is added to the queue of tablets waiting for a compaction thread. Once a thread is available, the gatherInformation(MajorCompactionRequest) method is called outside the tablets' lock. This gives the strategy the ability to read information that maybe expensive to fetch. Once the gatherInformation returns, the tablet lock is grabbed and the compactionPlan computed. This should *not* do expensive operations, especially not I/O. Note that the number of files may change between calls to gatherInformation(MajorCompactionRequest) and getCompactionPlan(MajorCompactionRequest).

Note: the strategy object used for the shouldCompact(MajorCompactionRequest) call is going to be different from the one used in the compaction thread.

Constructor Summary

Constructors

Constructor and Description
CompactionStrategy()

Method Summary

Modifier and Type	Method and Description
void	gatherInformation(MajorCompactionRequest request) Called prior to obtaining the tablet lock, useful for examining metadata or indexes.
abstract CompactionPlan	getCompactionPlan(MajorCompactionRequest request) Get the plan for compacting a tablets files.
void	init(Map<String,String> options) The settings for the compaction strategy pulled from zookeeper.
abstract boolean	shouldCompact(MajorCompactionRequest request) Determine if this tablet is eligible for a major compaction.

Methods inherited from class java.lang.Object

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

Constructor Detail

CompactionStrategy

public CompactionStrategy()

Method Detail

init

public void init(Map<String,String> options)

The settings for the compaction strategy pulled from zookeeper. The table.compacations.major.strategy.opts part of the setting will be removed.

shouldCompact

public abstract boolean shouldCompact(MajorCompactionRequest request)
                               throws IOException

Determine if this tablet is eligible for a major compaction. It's ok if it later determines (through gatherInformation(MajorCompactionRequest) and getCompactionPlan(MajorCompactionRequest)) that it does not need to. Any state stored during shouldCompact will no longer exist when gatherInformation(MajorCompactionRequest) and getCompactionPlan(MajorCompactionRequest) are called.

Called while holding the tablet lock, so it should not be doing any blocking.

Since no blocking should be done in this method, then its unexpected that this method will throw IOException. However since its in the API, it can not be easily removed.

Throws:

IOException

gatherInformation

public void gatherInformation(MajorCompactionRequest request)
                       throws IOException

Called prior to obtaining the tablet lock, useful for examining metadata or indexes. State collected during this method will be available during the call the getCompactionPlan(MajorCompactionRequest).

Parameters:

request - basic details about the tablet

Throws:

IOException

getCompactionPlan

public abstract CompactionPlan getCompactionPlan(MajorCompactionRequest request)
                                          throws IOException

Get the plan for compacting a tablets files. Called while holding the tablet lock, so it should not be doing any blocking.

Since no blocking should be done in this method, then its unexpected that this method will throw IOException. However since its in the API, it can not be easily removed.

Parameters:

request - basic details about the tablet

Returns:

the plan for a major compaction, or null to cancel the compaction.

Throws:

IOException