参考源码
elasticsearch5.6.12 lucene6.6.1 

lucene
flush  将内存中的segment写到磁盘但不执行fileChannel.force一部分数据会在buffer中
commit 调用force，将buffer中的数据写到磁盘


elasticsearch
refresh 调用lucene的flush
flush   调用lucene的commit




lucene flush

DocumentsWriter.doFlush
DocumentsWriterPerThread.flush
DefaultIndexingChain.flush
// nvd nvm文件
writeNorms
writeDocValues
// dii dim文件
writePoints
// fdt, fdx文件 
storedFieldsConsumer.flush
// doc, pos, tim, tip文件
termsHash.flush
// fnm文件
docWriter.codec.fieldInfosFormat().write
// cfs, cfe, si, liv 文件
DocumentsWriterPerThread.sealFlushedSegment
// 删除cfs, cfe, si, liv 之外的文件
IndexWriter.doAfterFlush


flush 相关配置
maxBufferedDocs
ramBufferSizeMB
perThreadHardLimitMB


Lucene  commit 

commit执行fileChannel.force，将buffer中的数据写到磁盘

flush all segments 
执行合并 maybeMerge，满足merge条件则合并

IndexWriter.commit
IndexWriter.commitInternal
IndexWriter.prepareCommitInternal
// flush segments 
DocumentsWriter.flushAllThreads
// sync 
IndexWriter.startCommit
Directory.sync
IOUtils.fsync
FileChannel.force
FileChannelImpl.force
// 更新commit信息segments_n，删除旧的segments_n-1
IndexWriter.finishCommit
// 满足merge条件则merge
IndexWriter.maybeMerge


Lucene maybeMerge

merge 异步执行

合并小段 ，大段不合并

IndexWriter.maybeMerge
IndexWriter.updatePendingMerges
// 查找可merge的segments
TieredMergePolicy.findMerges
// 执行merge
ConcurrentMergeScheduler.merge
// 异步执行merge 
MergeThread



es refresh

refresh_interval
indices.memory.index_buffer_size

InternalEngine.refresh
// lucene refresh
ReferenceManager.maybeRefreshBlocking
DirectoryReader.openIfChanged
StandardDirectoryReader.doOpenIfChanged
IndexWriter.getReader
// flush segments
DocumentsWriter.flushAllThreads
IndexWriter.maybeMerge



es flush

translog.ckp
translog-n.tlog

InternalEngine.flush
// prepareCommit translog
Translog.prepareCommit
// es commit index writer
InternalEngine.commitIndexWriter
// lucene commit
IndexWriter.commit
InternalEngine.refresh
Translog.commit




 elasticsearch中refresh和flush区别