io.atomix.copycat.server.storage.compaction

Class MinorCompactionManager

java.lang.Object

io.atomix.copycat.server.storage.compaction.MinorCompactionManager

All Implemented Interfaces:

CompactionManager

public final class MinorCompactionManager
extends Object
implements CompactionManager

Builds tasks for the Compaction.MINOR compaction process.

Minor compaction works by rewriting individual segments to remove entries that don't have to be removed sequentially from the log. The minor compaction manager is responsible for building a list of MinorCompactionTasks to compact segments. In the case of minor compaction, each task is responsible for compacting a single segment. However, in order to ensure segments are not compacted without cause, this compaction manager attempts to prioritize segments for which compaction will result in greater disk space savings.

Segments are selected for minor compaction based on several factors:

• The number of entries in the segment that have been released
• The number of times the segment has been compacted already

Given the number of entries that have been released from the segment, a percentage of entries reclaimed by compacting the segment is calculated. Then, the percentage of entries that have been released is multiplied by the number of times the segment has been compacted. If the result of this calculation is greater than the configured Storage.compactionThreshold() then the segment is selected for compaction.

The final formula is as follows:

   
   if ((segment.releaseCount() / (double) segment.count()) * segment.descriptor().version() > storage.compactionThreshold()) {
     // Compact the segment
   }
   
 

Author:

Method Summary

Modifier and Type	Method and Description
List<CompactionTask>	buildTasks(Storage storage, SegmentManager segments) Builds compaction tasks for the given segments.

Methods inherited from class java.lang.Object

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

Method Detail

buildTasks

public List<CompactionTask> buildTasks(Storage storage,
                                       SegmentManager segments)

Description copied from interface: CompactionManager

Builds compaction tasks for the given segments.

The collection of compaction tasks will be run in parallel in a pool of Storage.compactionThreads() background threads. Implementations should ensure that individual tasks can be run in parallel by operating on different segments in the log.

Specified by:

buildTasks in interface CompactionManager

Parameters:

storage - The storage configuration.

segments - The segments for which to build compaction tasks.

Returns:

An iterable of compaction tasks.