下面列出了org.apache.lucene.search.SearcherFactory#org.elasticsearch.common.lucene.Lucene 实例代码，或者点击链接到github查看源代码，也可以在右侧发表评论。
private static LocalCheckpointTracker createLocalCheckpointTracker(EngineConfig engineConfig, SegmentInfos lastCommittedSegmentInfos,
Logger logger, Supplier<Searcher> searcherSupplier, BiFunction<Long, Long, LocalCheckpointTracker> localCheckpointTrackerSupplier) {
try {
final SequenceNumbers.CommitInfo seqNoStats =
SequenceNumbers.loadSeqNoInfoFromLuceneCommit(lastCommittedSegmentInfos.userData.entrySet());
final long maxSeqNo = seqNoStats.maxSeqNo;
final long localCheckpoint = seqNoStats.localCheckpoint;
logger.trace("recovered maximum sequence number [{}] and local checkpoint [{}]", maxSeqNo, localCheckpoint);
final LocalCheckpointTracker tracker = localCheckpointTrackerSupplier.apply(maxSeqNo, localCheckpoint);
// Operations that are optimized using max_seq_no_of_updates optimization must not be processed twice; otherwise, they will
// create duplicates in Lucene. To avoid this we check the LocalCheckpointTracker to see if an operation was already processed.
// Thus, we need to restore the LocalCheckpointTracker bit by bit to ensure the consistency between LocalCheckpointTracker and
// Lucene index. This is not the only solution since we can bootstrap max_seq_no_of_updates with max_seq_no of the commit to
// disable the MSU optimization during recovery. Here we prefer to maintain the consistency of LocalCheckpointTracker.
if (localCheckpoint < maxSeqNo && engineConfig.getIndexSettings().isSoftDeleteEnabled()) {
try (Searcher searcher = searcherSupplier.get()) {
Lucene.scanSeqNosInReader(searcher.getDirectoryReader(), localCheckpoint + 1, maxSeqNo,
tracker::markSeqNoAsCompleted);
}
}
return tracker;
} catch (IOException ex) {
throw new EngineCreationFailureException(engineConfig.getShardId(), "failed to create local checkpoint tracker", ex);
}
}
private void refreshLastCommittedSegmentInfos() {
/*
* we have to inc-ref the store here since if the engine is closed by a tragic event
* we don't acquire the write lock and wait until we have exclusive access. This might also
* dec the store reference which can essentially close the store and unless we can inc the reference
* we can't use it.
*/
store.incRef();
try {
// reread the last committed segment infos
lastCommittedSegmentInfos = store.readLastCommittedSegmentsInfo();
} catch (Exception e) {
if (isClosed.get() == false) {
try {
logger.warn("failed to read latest segment infos on flush", e);
} catch (Exception inner) {
e.addSuppressed(inner);
}
if (Lucene.isCorruptionException(e)) {
throw new FlushFailedEngineException(shardId, e);
}
}
} finally {
store.decRef();
}
}
@Override
public void readFrom(StreamInput in) throws IOException {
super.readFrom(in);
recoveryId = in.readLong();
shardId = ShardId.readShardId(in);
String name = in.readString();
position = in.readVLong();
long length = in.readVLong();
String checksum = in.readOptionalString();
content = in.readBytesReference();
Version writtenBy = null;
String versionString = in.readOptionalString();
writtenBy = Lucene.parseVersionLenient(versionString, null);
metaData = new StoreFileMetaData(name, length, checksum, writtenBy);
lastChunk = in.readBoolean();
totalTranslogOps = in.readVInt();
sourceThrottleTimeInNanos = in.readLong();
}
@Override
public void collect(int doc) throws IOException {
final Query query = getQuery(doc);
if (query == null) {
// log???
return;
}
Query existsQuery = query;
if (isNestedDoc) {
existsQuery = new BooleanQuery.Builder()
.add(existsQuery, Occur.MUST)
.add(Queries.newNonNestedFilter(), Occur.FILTER)
.build();
}
// run the query
try {
if (Lucene.exists(searcher, existsQuery)) {
topDocsLeafCollector.collect(doc);
postMatch(doc);
}
} catch (IOException e) {
logger.warn("[" + current.utf8ToString() + "] failed to execute query", e);
}
}
@Override
public void collect(int doc) throws IOException {
final Query query = getQuery(doc);
if (query == null) {
// log???
return;
}
Query existsQuery = query;
if (isNestedDoc) {
existsQuery = new BooleanQuery.Builder()
.add(existsQuery, Occur.MUST)
.add(Queries.newNonNestedFilter(), Occur.FILTER)
.build();
}
// run the query
try {
if (Lucene.exists(searcher, existsQuery)) {
counter++;
postMatch(doc);
}
} catch (IOException e) {
logger.warn("[" + current.utf8ToString() + "] failed to execute query", e);
}
}
@Override
public LeafBucketCollector getLeafCollector(LeafReaderContext ctx,
final LeafBucketCollector sub) throws IOException {
// no need to provide deleted docs to the filter
final Bits[] bits = new Bits[filters.length];
for (int i = 0; i < filters.length; ++i) {
bits[i] = Lucene.asSequentialAccessBits(ctx.reader().maxDoc(), filters[i].scorer(ctx));
}
return new LeafBucketCollectorBase(sub, null) {
@Override
public void collect(int doc, long bucket) throws IOException {
boolean matched = false;
for (int i = 0; i < bits.length; i++) {
if (bits[i].get(doc)) {
collectBucket(sub, doc, bucketOrd(bucket, i));
matched = true;
}
}
if (showOtherBucket && !matched) {
collectBucket(sub, doc, bucketOrd(bucket, bits.length));
}
}
};
}
@Override
public void readFrom(StreamInput in) throws IOException {
super.readFrom(in);
id = in.readLong();
size = in.readVInt();
docIds = new int[size];
for (int i = 0; i < size; i++) {
docIds[i] = in.readVInt();
}
byte flag = in.readByte();
if (flag == 1) {
lastEmittedDoc = Lucene.readFieldDoc(in);
} else if (flag == 2) {
lastEmittedDoc = Lucene.readScoreDoc(in);
} else if (flag != 0) {
throw new IOException("Unknown flag: " + flag);
}
}
@Override
public void writeTo(StreamOutput out) throws IOException {
super.writeTo(out);
out.writeLong(id);
out.writeVInt(size);
for (int i = 0; i < size; i++) {
out.writeVInt(docIds[i]);
}
if (lastEmittedDoc == null) {
out.writeByte((byte) 0);
} else if (lastEmittedDoc instanceof FieldDoc) {
out.writeByte((byte) 1);
Lucene.writeFieldDoc(out, (FieldDoc) lastEmittedDoc);
} else {
out.writeByte((byte) 2);
Lucene.writeScoreDoc(out, lastEmittedDoc);
}
}
@Override
public void readFrom(StreamInput in) throws IOException {
name = in.readString();
generation = Long.parseLong(name.substring(1), Character.MAX_RADIX);
committed = in.readBoolean();
search = in.readBoolean();
docCount = in.readInt();
delDocCount = in.readInt();
sizeInBytes = in.readLong();
version = Lucene.parseVersionLenient(in.readOptionalString(), null);
compound = in.readOptionalBoolean();
mergeId = in.readOptionalString();
memoryInBytes = in.readLong();
if (in.readBoolean()) {
// verbose mode
ramTree = readRamTree(in);
}
}
/**
* Read the last segments info from the commit pointed to by the searcher manager
*/
protected static SegmentInfos readLastCommittedSegmentInfos(final SearcherManager sm, final Store store) throws IOException {
IndexSearcher searcher = sm.acquire();
try {
IndexCommit latestCommit = ((DirectoryReader) searcher.getIndexReader()).getIndexCommit();
return Lucene.readSegmentInfos(latestCommit);
} catch (IOException e) {
// Fall back to reading from the store if reading from the commit fails
try {
return store. readLastCommittedSegmentsInfo();
} catch (IOException e2) {
e2.addSuppressed(e);
throw e2;
}
} finally {
sm.release(searcher);
}
}
@Override
public Scorer scorer(LeafReaderContext context) throws IOException {
DocIdSet childrenDocSet = childrenFilter.getDocIdSet(context, null);
// we forcefully apply live docs here so that deleted children don't give matching parents
childrenDocSet = BitsFilteredDocIdSet.wrap(childrenDocSet, context.reader().getLiveDocs());
if (Lucene.isEmpty(childrenDocSet)) {
return null;
}
final DocIdSetIterator childIterator = childrenDocSet.iterator();
if (childIterator == null) {
return null;
}
SortedDocValues bytesValues = globalIfd.load(context).getOrdinalsValues(parentType);
if (bytesValues == null) {
return null;
}
return new ChildScorer(this, parentIdxs, scores, childIterator, bytesValues);
}
@Override
public Scorer scorer(LeafReaderContext context) throws IOException {
DocIdSet childrenDocIdSet = childrenFilter.getDocIdSet(context, null);
if (Lucene.isEmpty(childrenDocIdSet)) {
return null;
}
SortedDocValues globalValues = globalIfd.load(context).getOrdinalsValues(parentType);
if (globalValues != null) {
// we forcefully apply live docs here so that deleted children don't give matching parents
childrenDocIdSet = BitsFilteredDocIdSet.wrap(childrenDocIdSet, context.reader().getLiveDocs());
DocIdSetIterator innerIterator = childrenDocIdSet.iterator();
if (innerIterator != null) {
ChildrenDocIdIterator childrenDocIdIterator = new ChildrenDocIdIterator(
innerIterator, parentOrds, globalValues
);
return ConstantScorer.create(childrenDocIdIterator, this, queryWeight);
}
}
return null;
}
protected void setupFieldType(BuilderContext context) {
fieldType.setNames(buildNames(context));
if (fieldType.indexAnalyzer() == null && fieldType.tokenized() == false && fieldType.indexOptions() != IndexOptions.NONE) {
fieldType.setIndexAnalyzer(Lucene.KEYWORD_ANALYZER);
fieldType.setSearchAnalyzer(Lucene.KEYWORD_ANALYZER);
}
if (fieldDataSettings != null) {
Settings settings = Settings.builder().put(fieldType.fieldDataType().getSettings()).put(fieldDataSettings).build();
fieldType.setFieldDataType(new FieldDataType(fieldType.fieldDataType().getType(), settings));
}
boolean defaultDocValues = false; // pre 2.0
if (context.indexCreatedVersion().onOrAfter(Version.V_2_0_0_beta1)) {
defaultDocValues = fieldType.tokenized() == false && fieldType.indexOptions() != IndexOptions.NONE;
}
// backcompat for "fielddata: format: docvalues" for now...
boolean fieldDataDocValues = fieldType.fieldDataType() != null
&& FieldDataType.DOC_VALUES_FORMAT_VALUE.equals(fieldType.fieldDataType().getFormat(context.indexSettings()));
if (fieldDataDocValues && docValuesSet && fieldType.hasDocValues() == false) {
// this forces the doc_values setting to be written, so fielddata does not mask the original setting
defaultDocValues = true;
}
defaultFieldType.setHasDocValues(defaultDocValues);
if (docValuesSet == false) {
fieldType.setHasDocValues(defaultDocValues || fieldDataDocValues);
}
}
@Before
public void setupIndex() throws Exception {
dir = new ByteBuffersDirectory();
try(IndexWriter indexWriter = new IndexWriter(dir, new IndexWriterConfig(Lucene.STANDARD_ANALYZER))) {
for (int i = 0; i < docs.length; i++) {
Document doc = new Document();
doc.add(new Field("_id", Integer.toString(i + 1), StoredField.TYPE));
doc.add(newTextField("text", docs[i], Field.Store.YES));
indexWriter.addDocument(doc);
}
}
reader = DirectoryReader.open(dir);
searcher = new IndexSearcher(reader);
}
@Inject
public AnnotationIndicesAnalysis(Settings settings,
IndicesAnalysisService indicesAnalysisService) {
super(settings);
indicesAnalysisService.analyzerProviderFactories().put(
"default",
new PreBuiltAnalyzerProviderFactory("default",
AnalyzerScope.INDICES, new AnnotationAnalyzer(
Lucene.ANALYZER_VERSION)));
indicesAnalysisService.tokenFilterFactories().put("annotation_filter",
new PreBuiltTokenFilterFactoryFactory(new TokenFilterFactory() {
@Override
public String name() {
return "annotation_filter";
}
@Override
public TokenStream create(TokenStream tokenStream) {
return new InlineAnnotationFilter(tokenStream);
}
}));
}
protected final DocsStats docsStats(IndexReader indexReader) {
long numDocs = 0;
long numDeletedDocs = 0;
long sizeInBytes = 0;
// we don't wait for a pending refreshes here since it's a stats call instead we mark it as accessed only which will cause
// the next scheduled refresh to go through and refresh the stats as well
for (LeafReaderContext readerContext : indexReader.leaves()) {
// we go on the segment level here to get accurate numbers
final SegmentReader segmentReader = Lucene.segmentReader(readerContext.reader());
SegmentCommitInfo info = segmentReader.getSegmentInfo();
numDocs += readerContext.reader().numDocs();
numDeletedDocs += readerContext.reader().numDeletedDocs();
try {
sizeInBytes += info.sizeInBytes();
} catch (IOException e) {
logger.trace(() -> new ParameterizedMessage("failed to get size for [{}]", info.info.name), e);
}
}
return new DocsStats(numDocs, numDeletedDocs, sizeInBytes);
}
private void refreshLastCommittedSegmentInfos() {
/*
* we have to inc-ref the store here since if the engine is closed by a tragic event
* we don't acquire the write lock and wait until we have exclusive access. This might also
* dec the store reference which can essentially close the store and unless we can inc the reference
* we can't use it.
*/
store.incRef();
try {
// reread the last committed segment infos
lastCommittedSegmentInfos = store.readLastCommittedSegmentsInfo();
} catch (Exception e) {
if (isClosed.get() == false) {
try {
logger.warn("failed to read latest segment infos on flush", e);
} catch (Exception inner) {
e.addSuppressed(inner);
}
if (Lucene.isCorruptionException(e)) {
throw new FlushFailedEngineException(shardId, e);
}
}
} finally {
store.decRef();
}
}
@Override
protected BytesRef indexedValueForSearch(Object value) {
if (searchAnalyzer() == Lucene.KEYWORD_ANALYZER) {
// keyword analyzer with the default attribute source which encodes terms using UTF8
// in that case we skip normalization, which may be slow if there many terms need to
// parse (eg. large terms query) since Analyzer.normalize involves things like creating
// attributes through reflection
// This if statement will be used whenever a normalizer is NOT configured
return super.indexedValueForSearch(value);
}
if (value == null) {
return null;
}
if (value instanceof BytesRef) {
value = ((BytesRef) value).utf8ToString();
}
return searchAnalyzer().normalize(name(), value.toString());
}
@Override
public void shardFailed(ShardRouting failedShard, UnassignedInfo unassignedInfo) {
if (failedShard.primary() && failedShard.initializing()) {
RecoverySource recoverySource = failedShard.recoverySource();
if (recoverySource.getType() == RecoverySource.Type.SNAPSHOT) {
Snapshot snapshot = ((SnapshotRecoverySource) recoverySource).snapshot();
// mark restore entry for this shard as failed when it's due to a file corruption. There is no need wait on retries
// to restore this shard on another node if the snapshot files are corrupt. In case where a node just left or crashed,
// however, we only want to acknowledge the restore operation once it has been successfully restored on another node.
if (unassignedInfo.getFailure() != null && Lucene.isCorruptionException(unassignedInfo.getFailure().getCause())) {
changes(snapshot).shards.put(failedShard.shardId(), new ShardRestoreStatus(failedShard.currentNodeId(),
RestoreInProgress.State.FAILURE, unassignedInfo.getFailure().getCause().getMessage()));
}
}
}
}
protected InternalEngine createEngine(@Nullable IndexWriterFactory indexWriterFactory,
@Nullable BiFunction<Long, Long, LocalCheckpointTracker> localCheckpointTrackerSupplier,
@Nullable ToLongBiFunction<Engine, Engine.Operation> seqNoForOperation,
EngineConfig config) throws IOException {
final Store store = config.getStore();
final Directory directory = store.directory();
if (Lucene.indexExists(directory) == false) {
store.createEmpty();
final String translogUuid = Translog.createEmptyTranslog(config.getTranslogConfig().getTranslogPath(),
SequenceNumbers.NO_OPS_PERFORMED, shardId, primaryTerm.get());
store.associateIndexWithNewTranslog(translogUuid);
}
InternalEngine internalEngine = createInternalEngine(indexWriterFactory, localCheckpointTrackerSupplier, seqNoForOperation, config);
internalEngine.recoverFromTranslog(translogHandler, Long.MAX_VALUE);
return internalEngine;
}
private IndexWriterConfig getIndexWriterConfig() {
final IndexWriterConfig iwc = new IndexWriterConfig(engineConfig.getAnalyzer());
iwc.setCommitOnClose(false); // we by default don't commit on close
iwc.setOpenMode(IndexWriterConfig.OpenMode.APPEND);
iwc.setIndexDeletionPolicy(combinedDeletionPolicy);
// with tests.verbose, lucene sets this up: plumb to align with filesystem stream
boolean verbose = false;
try {
verbose = Boolean.parseBoolean(System.getProperty("tests.verbose"));
} catch (Exception ignore) {
}
iwc.setInfoStream(verbose ? InfoStream.getDefault() : new LoggerInfoStream(logger));
iwc.setMergeScheduler(mergeScheduler);
// Give us the opportunity to upgrade old segments while performing
// background merges
MergePolicy mergePolicy = config().getMergePolicy();
// always configure soft-deletes field so an engine with soft-deletes disabled can open a Lucene index with soft-deletes.
iwc.setSoftDeletesField(Lucene.SOFT_DELETES_FIELD);
if (softDeleteEnabled) {
mergePolicy = new RecoverySourcePruneMergePolicy(SourceFieldMapper.RECOVERY_SOURCE_NAME, softDeletesPolicy::getRetentionQuery,
new SoftDeletesRetentionMergePolicy(Lucene.SOFT_DELETES_FIELD, softDeletesPolicy::getRetentionQuery, mergePolicy));
}
iwc.setMergePolicy(new ElasticsearchMergePolicy(mergePolicy));
iwc.setSimilarity(engineConfig.getSimilarity());
iwc.setRAMBufferSizeMB(engineConfig.getIndexingBufferSize().getMbFrac());
iwc.setCodec(engineConfig.getCodec());
iwc.setUseCompoundFile(true); // always use compound on flush - reduces # of file-handles on refresh
if (config().getIndexSort() != null) {
iwc.setIndexSort(config().getIndexSort());
}
return iwc;
}
@Override
public void collect(int doc) throws IOException {
final Query query = getQuery(doc);
if (query == null) {
// log???
return;
}
Query existsQuery = query;
if (isNestedDoc) {
existsQuery = new BooleanQuery.Builder()
.add(existsQuery, Occur.MUST)
.add(Queries.newNonNestedFilter(), Occur.FILTER)
.build();
}
// run the query
try {
if (context.highlight() != null) {
context.parsedQuery(new ParsedQuery(query));
context.hitContext().cache().clear();
}
if (Lucene.exists(searcher, existsQuery)) {
if (!limit || counter < size) {
matches.add(BytesRef.deepCopyOf(current));
if (context.highlight() != null) {
highlightPhase.hitExecute(context, context.hitContext());
hls.add(context.hitContext().hit().getHighlightFields());
}
}
counter++;
postMatch(doc);
}
} catch (IOException e) {
logger.warn("[" + current.utf8ToString() + "] failed to execute query", e);
}
}
@Override
public void collect(int doc) throws IOException {
final Query query = getQuery(doc);
if (query == null) {
// log???
return;
}
Query existsQuery = query;
if (isNestedDoc) {
existsQuery = new BooleanQuery.Builder()
.add(existsQuery, Occur.MUST)
.add(Queries.newNonNestedFilter(), Occur.FILTER)
.build();
}
// run the query
try {
if (context.highlight() != null) {
context.parsedQuery(new ParsedQuery(query));
context.hitContext().cache().clear();
}
if (Lucene.exists(searcher, existsQuery)) {
if (!limit || counter < size) {
matches.add(BytesRef.deepCopyOf(current));
scores.add(scorer.score());
if (context.highlight() != null) {
highlightPhase.hitExecute(context, context.hitContext());
hls.add(context.hitContext().hit().getHighlightFields());
}
}
counter++;
postMatch(doc);
}
} catch (IOException e) {
logger.warn("[" + current.utf8ToString() + "] failed to execute query", e);
}
}
@Override
protected void doWriteTo(StreamOutput out) throws IOException {
out.writeVInt(from);
out.writeVInt(size);
Lucene.writeTopDocs(out, topDocs);
searchHits.writeTo(out);
}
@Override
public LeafBucketCollector getLeafCollector(LeafReaderContext ctx,
final LeafBucketCollector sub) throws IOException {
// no need to provide deleted docs to the filter
final Bits bits = Lucene.asSequentialAccessBits(ctx.reader().maxDoc(), filter.scorer(ctx));
return new LeafBucketCollectorBase(sub, null) {
@Override
public void collect(int doc, long bucket) throws IOException {
if (bits.get(doc)) {
collectBucket(sub, doc, bucket);
}
}
};
}
@Override
public TopDocs topDocs(SearchContext context, FetchSubPhase.HitContext hitContext) throws IOException {
Query rawParentFilter;
if (parentObjectMapper == null) {
rawParentFilter = Queries.newNonNestedFilter();
} else {
rawParentFilter = parentObjectMapper.nestedTypeFilter();
}
BitSetProducer parentFilter = context.bitsetFilterCache().getBitSetProducer(rawParentFilter);
Query childFilter = childObjectMapper.nestedTypeFilter();
Query q = Queries.filtered(query.query(), new NestedChildrenQuery(parentFilter, childFilter, hitContext));
if (size() == 0) {
return new TopDocs(context.searcher().count(q), Lucene.EMPTY_SCORE_DOCS, 0);
} else {
int topN = Math.min(from() + size(), context.searcher().getIndexReader().maxDoc());
TopDocsCollector topDocsCollector;
if (sort() != null) {
try {
topDocsCollector = TopFieldCollector.create(sort(), topN, true, trackScores(), trackScores());
} catch (IOException e) {
throw ExceptionsHelper.convertToElastic(e);
}
} else {
topDocsCollector = TopScoreDocCollector.create(topN);
}
try {
context.searcher().search(q, topDocsCollector);
} finally {
clearReleasables(Lifetime.COLLECTION);
}
return topDocsCollector.topDocs(from(), size());
}
}
private void processFailure(SearchContext context, Throwable t) {
freeContext(context.id());
try {
if (Lucene.isCorruptionException(t)) {
context.indexShard().failShard("search execution corruption failure", t);
}
} catch (Throwable e) {
logger.warn("failed to process shard failure to (potentially) send back shard failure on corruption", e);
}
}
/**
* fail engine due to some error. the engine will also be closed.
* The underlying store is marked corrupted iff failure is caused by index corruption
*/
public void failEngine(String reason, @Nullable Throwable failure) {
if (failEngineLock.tryLock()) {
store.incRef();
try {
try {
// we just go and close this engine - no way to recover
closeNoLock("engine failed on: [" + reason + "]");
} finally {
if (failedEngine != null) {
logger.debug("tried to fail engine but engine is already failed. ignoring. [{}]", failure, reason);
return;
}
logger.warn("failed engine [{}]", failure, reason);
// we must set a failure exception, generate one if not supplied
failedEngine = (failure != null) ? failure : new IllegalStateException(reason);
// we first mark the store as corrupted before we notify any listeners
// this must happen first otherwise we might try to reallocate so quickly
// on the same node that we don't see the corrupted marker file when
// the shard is initializing
if (Lucene.isCorruptionException(failure)) {
try {
store.markStoreCorrupted(new IOException("failed engine (reason: [" + reason + "])", ExceptionsHelper.unwrapCorruption(failure)));
} catch (IOException e) {
logger.warn("Couldn't mark store corrupted", e);
}
}
failedEngineListener.onFailedEngine(shardId, reason, failure);
}
} catch (Throwable t) {
// don't bubble up these exceptions up
logger.warn("failEngine threw exception", t);
} finally {
store.decRef();
}
} else {
logger.debug("tried to fail engine but could not acquire lock - engine should be failed by now [{}]", failure, reason);
}
}
/** Check whether the engine should be failed */
protected boolean maybeFailEngine(String source, Throwable t) {
if (Lucene.isCorruptionException(t)) {
failEngine("corrupt file (source: [" + source + "])", t);
return true;
} else if (ExceptionsHelper.isOOM(t)) {
failEngine("out of memory (source: [" + source + "])", t);
return true;
} else if (t instanceof RecoveryFromDistributedLogFailedException) {
failEngine("recovery from distributed log service failed", t);
return true;
}
return false;
}
public CommitStats(SegmentInfos segmentInfos) {
// clone the map to protect against concurrent changes
userData = MapBuilder.<String, String>newMapBuilder().putAll(segmentInfos.getUserData()).immutableMap();
// lucene calls the current generation, last generation.
generation = segmentInfos.getLastGeneration();
if (segmentInfos.getId() != null) { // id is only written starting with Lucene 5.0
id = Base64.encodeBytes(segmentInfos.getId());
}
numDocs = Lucene.getNumDocs(segmentInfos);
}