public abstract class MergePolicy extends Object implements Closeable, Cloneable
Expert: a MergePolicy determines the sequence of primitive merge operations.
Whenever the segments in an index have been altered by
IndexWriter
, either the addition of a newly
flushed segment, addition of many segments from
addIndexes* calls, or a previous merge that may now need
to cascade, IndexWriter
invokes findMerges(org.apache.lucene.index.SegmentInfos)
to give the MergePolicy a chance to pick
merges that are now required. This method returns a
MergePolicy.MergeSpecification
instance describing the set of
merges that should be done, or null if no merges are
necessary. When IndexWriter.forceMerge is called, it calls
findForcedMerges(SegmentInfos,int,Map)
and the MergePolicy should
then return the necessary merges.
Note that the policy can return more than one merge at
a time. In this case, if the writer is using SerialMergeScheduler
, the merges will be run
sequentially but if it is using ConcurrentMergeScheduler
they will be run concurrently.
The default MergePolicy is TieredMergePolicy
.
Modifier and Type | Class and Description |
---|---|
static class |
MergePolicy.MergeAbortedException
Thrown when a merge was explicity aborted because
IndexWriter.close(boolean) was called with
false . |
static class |
MergePolicy.MergeException
Exception thrown if there are any problems while
executing a merge.
|
static class |
MergePolicy.MergeSpecification
A MergeSpecification instance provides the information
necessary to perform multiple merges.
|
static class |
MergePolicy.OneMerge
OneMerge provides the information necessary to perform
an individual primitive merge operation, resulting in
a single new segment.
|
Modifier and Type | Field and Description |
---|---|
protected SetOnce<IndexWriter> |
writer
IndexWriter that contains this instance. |
Constructor and Description |
---|
MergePolicy()
Creates a new merge policy instance.
|
Modifier and Type | Method and Description |
---|---|
MergePolicy |
clone() |
abstract void |
close()
Release all resources for the policy.
|
abstract MergePolicy.MergeSpecification |
findForcedDeletesMerges(SegmentInfos segmentInfos)
Determine what set of merge operations is necessary in order to expunge all
deletes from the index.
|
abstract MergePolicy.MergeSpecification |
findForcedMerges(SegmentInfos segmentInfos,
int maxSegmentCount,
Map<SegmentInfoPerCommit,Boolean> segmentsToMerge)
Determine what set of merge operations is necessary in
order to merge to <= the specified segment count.
|
abstract MergePolicy.MergeSpecification |
findMerges(SegmentInfos segmentInfos)
Determine what set of merge operations are now necessary on the index.
|
void |
setIndexWriter(IndexWriter writer)
Sets the
IndexWriter to use by this merge policy. |
abstract boolean |
useCompoundFile(SegmentInfos segments,
SegmentInfoPerCommit newSegment)
Returns true if a new segment (regardless of its origin) should use the compound file format.
|
protected SetOnce<IndexWriter> writer
IndexWriter
that contains this instance.public MergePolicy()
IndexWriter
, you should call
setIndexWriter(IndexWriter)
.public MergePolicy clone()
public void setIndexWriter(IndexWriter writer)
IndexWriter
to use by this merge policy. This method is
allowed to be called only once, and is usually set by IndexWriter. If it is
called more than once, SetOnce.AlreadySetException
is thrown.SetOnce
public abstract MergePolicy.MergeSpecification findMerges(SegmentInfos segmentInfos) throws IOException
IndexWriter
calls this whenever there is a change to the segments.
This call is always synchronized on the IndexWriter
instance so
only one thread at a time will call this method.segmentInfos
- the total set of segments in the indexIOException
public abstract MergePolicy.MergeSpecification findForcedMerges(SegmentInfos segmentInfos, int maxSegmentCount, Map<SegmentInfoPerCommit,Boolean> segmentsToMerge) throws IOException
IndexWriter
calls this when its
IndexWriter.forceMerge(int)
method is called. This call is always
synchronized on the IndexWriter
instance so only one thread at a
time will call this method.segmentInfos
- the total set of segments in the indexmaxSegmentCount
- requested maximum number of segments in the index (currently this
is always 1)segmentsToMerge
- contains the specific SegmentInfo instances that must be merged
away. This may be a subset of all
SegmentInfos. If the value is True for a
given SegmentInfo, that means this segment was
an original segment present in the
to-be-merged index; else, it was a segment
produced by a cascaded merge.IOException
public abstract MergePolicy.MergeSpecification findForcedDeletesMerges(SegmentInfos segmentInfos) throws IOException
segmentInfos
- the total set of segments in the indexIOException
public abstract void close()
public abstract boolean useCompoundFile(SegmentInfos segments, SegmentInfoPerCommit newSegment) throws IOException
IOException
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