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https://issues.apache.org/jira/browse/HDFS-1435?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12917876#action_12917876
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dhruba borthakur commented on HDFS-1435:
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+1 on compressing the entire file.
The VERSIONS file should have a entry of the form:
codec=org.apache.hadoop.io.compress.GzipCodec
if the fsimage has been compressed using gzip.
1. At namenode startup time, it reads the VERSIONS file to determine how the
fsimage is compressed. If the VERSIONS file does not have a codec=xxx entry,
then the NN assumes that the image is not compressed.
2. while saving the fsimage, the NN looks at its own configuration to see if a
config parameter named io.compression.codec is defined in the config. If it is
defined, then it uses that codec to compress the fsimage and also updates the
VERSIONS file.
This approach would be fully backward compatible and supports different
compression algorithms for fsimage.
> Provide an option to store fsimage compressed
> ---------------------------------------------
>
> Key: HDFS-1435
> URL: https://issues.apache.org/jira/browse/HDFS-1435
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: name-node
> Affects Versions: 0.22.0
> Reporter: Hairong Kuang
> Assignee: Hairong Kuang
> Fix For: 0.22.0
>
>
> Our HDFS has fsimage as big as 20G bytes. It consumes a lot of network
> bandwidth when secondary NN uploads a new fsimage to primary NN.
> If we could store fsimage compressed, the problem could be greatly alleviated.
> I plan to provide a new configuration hdfs.image.compressed with a default
> value of false. If it is set to be true, fsimage is stored as compressed.
> The fsimage will have a new layout with a new field "compressed" in its
> header, indicating if the namespace is stored compressed or not.
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