Org.elasticsearch.index.engine.FlushFailedEngineException

I am running elasticsearch 0.19.9 with 36 instances. I saw the following
exceptions. Is it safe to be ignored? Otherwise, how can I tune the
parameter?

[2012-09-25 17:40:26,436][WARN ][index.translog ] [Archimage]
[request_trace20120925][0] failed to flush shard on translog threshold
org.elasticsearch.index.engine.FlushFailedEngineException:
[request_trace20120925][0] Flush failed
at
org.elasticsearch.index.engine.robin.RobinEngine.flush(RobinEngine.java:903)
at
org.elasticsearch.index.shard.service.InternalIndexShard.flush(InternalIndexShard.java:467)
at
org.elasticsearch.index.translog.TranslogService$TranslogBasedFlush$1.run(TranslogService.java:191)
at
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.NullPointerException
at
org.elasticsearch.common.compress.BufferRecycler.releaseEncodeBuffer(BufferRecycler.java:68)
at
org.elasticsearch.common.compress.lzf.ChunkEncoder.close(ChunkEncoder.java:113)
at
org.elasticsearch.common.compress.lzf.LZFCompressedIndexOutput.doClose(LZFCompressedIndexOutput.java:63)
at
org.elasticsearch.common.compress.CompressedIndexOutput.close(CompressedIndexOutput.java:184)
at
org.elasticsearch.index.store.Store$StoreIndexOutput.close(Store.java:645)
at org.apache.lucene.util.IOUtils.close(IOUtils.java:141)
at org.apache.lucene.index.FieldsWriter.close(FieldsWriter.java:139)
at
org.apache.lucene.index.StoredFieldsWriter.flush(StoredFieldsWriter.java:55)
at
org.apache.lucene.index.DocFieldProcessor.flush(DocFieldProcessor.java:59)
at
org.apache.lucene.index.DocumentsWriter.flush(DocumentsWriter.java:581)
at
org.apache.lucene.index.IndexWriter.doFlush(IndexWriter.java:3587)
at org.apache.lucene.index.IndexWriter.prepareCommit(IndexWriter.java:3376)
at
org.apache.lucene.index.IndexWriter.commitInternal(IndexWriter.java:3485)
at org.apache.lucene.index.IndexWriter.commit(IndexWriter.java:3467)
at
org.elasticsearch.index.engine.robin.RobinEngine.flush(RobinEngine.java:871)
... 5 more

Thank you
Best, Jae

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