nkeywal created HBASE-6490:
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Summary: 'dfs.client.block.write.retries' value could be increased
in HBase
Key: HBASE-6490
URL: https://issues.apache.org/jira/browse/HBASE-6490
Project: HBase
Issue Type: Improvement
Components: master, regionserver
Affects Versions: 0.96.0
Environment: When allocating a new node during writing, hdfs tries
'dfs.client.block.write.retries' times (default 3) to write the block. When it
fails, it goes back to the nanenode for a new list, and raises an error if the
number of retries is reached. In HBase, if the error is while we're writing a
hlog file, it will trigger a region server abort (as hbase does not trust the
log anymore). For simple case (new, and as such empty log file), this seems to
be ok, and we don't lose data. There could be some complex cases if the error
occurs on a hlog file with already multiple blocks written.
Logs lines are:
"Exception in createBlockOutputStream", then "Abandoning block " followed by
"Excluding datanode " for a retry.
IOException: "Unable to create new block.", when the number of retries is
reached.
Probability of occurence seems quite low, (number of bad nodes / number of
nodes)^(number of retries), and it implies that you have a region server
without its datanode. But it's per new block.
Increasing the default value of 'dfs.client.block.write.retries' could make
sense to be better covered in chaotic conditions.
Reporter: nkeywal
Priority: Minor
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