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From Jean-Adrien <a...@jeanjean.ch>
Subject HBase behaviour at startup (compression)
Date Wed, 17 Dec 2008 11:08:39 GMT


I have a question regarding the behavior of HBase at startup time.
First the region servers load all regions of enabled tables, then a batch
task of (minor?) compression is made on some of these regions:

2008-12-17 11:04:46,688 INFO org.apache.hadoop.hbase.regionserver.HRegion:
starting compaction on region
2008-12-17 11:05:36,196 INFO org.apache.hadoop.hbase.regionserver.HRegion:
compaction completed on region
test-D-0.3,GST13927+129099482919-13927,1229196632010 in 49sec

What are the concerned regions ? All of them ? Only the region that have
been modified during the last roll of log ?
In my case it takes several hours to complete, since I have about 500
regions for 2 region servers. And if I have well  understood how hadoop
works, it yield that the entire hdfs content is rewritten during this phase,
since the file are written once. Isn't it ? 

If I disable and re-enable a table, must the compactions re-run ?

Thanks for your answers

-- Jean-Adrien

Cluster info:
hadoop: 0.18.1
hbase: 0.18.0 (jar of hadoop replaced with 0.18.1)

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