com.netflix.hollow.tools.compact

Class HollowCompactor

java.lang.Object

com.netflix.hollow.tools.compact.HollowCompactor

public class HollowCompactor
extends java.lang.Object

During a long delta chain, it's possible that a large number of holes in the ordinal space will exist in some types.

The HollowCompactor can reclaim space by moving records off of the high end of the ordinal space into these holes.

This is accomplished by producing deltas which only include removals and additions of identical records allocated to more optimal ordinals.

This must sometimes be accomplished with a series of deltas, because the remapping of one state will cause some removals/additions in referencing states (since they will point to new ordinals). In a single delta transition, the HollowCompactor will only attempt to compact a set of types which are not referencing each other (either directly or transitively).

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	HollowCompactor.CompactionConfig A configuration that specifies when a type is a candidate for compaction.

Constructor Summary

Constructors

Constructor and Description
HollowCompactor(HollowWriteStateEngine writeEngine, HollowReadStateEngine readEngine, HollowCompactor.CompactionConfig config) Provide the state engines on which to operate, and the criteria to identify when a compaction is necessary
HollowCompactor(HollowWriteStateEngine writeEngine, HollowReadStateEngine readEngine, long minCandidateHoleCostInBytes, int minCandidateHolePercentage) Provide the state engines on which to operate, and the criteria to identify when a compaction is necessary

Method Summary

Modifier and Type	Method and Description
void	compact() Perform a compaction.
boolean	needsCompaction() Determine whether a compaction is necessary, based on the criteria specified in the constructor.

Methods inherited from class java.lang.Object

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

Constructor Detail

HollowCompactor

public HollowCompactor(HollowWriteStateEngine writeEngine,
                       HollowReadStateEngine readEngine,
                       HollowCompactor.CompactionConfig config)

Provide the state engines on which to operate, and the criteria to identify when a compaction is necessary

Parameters:

writeEngine - the HollowWriteStateEngine to compact

readEngine - a HollowReadStateEngine at the same data state as the writeEngine

config - The criteria to identify when a compaction is necessary.

HollowCompactor

public HollowCompactor(HollowWriteStateEngine writeEngine,
                       HollowReadStateEngine readEngine,
                       long minCandidateHoleCostInBytes,
                       int minCandidateHolePercentage)

Provide the state engines on which to operate, and the criteria to identify when a compaction is necessary

Parameters:

writeEngine - the HollowWriteStateEngine to compact

readEngine - a HollowReadStateEngine at the same data state as the writeEngine

minCandidateHoleCostInBytes - identify a type as a candidate for compaction only when the bytes used by ordinal holes exceeds this value

minCandidateHolePercentage - identify a type as a candidate for compaction only when the percentage of space used by ordinal holes exceeds this value

Method Detail

needsCompaction

public boolean needsCompaction()

Determine whether a compaction is necessary, based on the criteria specified in the constructor.

Returns:

true if compaction is necessary, otherwise false

compact

public void compact()

Perform a compaction. It is expected that:

• the HollowWriteStateEngine supplied in the constructor is unmodified since the last call to HollowWriteStateEngine.prepareForNextCycle()
• the HollowReadStateEngine supplied in the constructor reflects the same state as the HollowWriteStateEngine.