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From "Jean-Daniel Cryans (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-7391) Review/improve HLog compression's memory consumption
Date Wed, 19 Dec 2012 16:17:12 GMT
Jean-Daniel Cryans created HBASE-7391:

             Summary: Review/improve HLog compression's memory consumption
                 Key: HBASE-7391
                 URL: https://issues.apache.org/jira/browse/HBASE-7391
             Project: HBase
          Issue Type: Bug
            Reporter: Jean-Daniel Cryans
             Fix For: 0.96.0

>From Ram in http://mail-archives.apache.org/mod_mbox/hbase-dev/201205.mbox/%3C00bc01cd31e6$7caf1320$760d3960$%25vasudevan@huawei.com%3E:

One small observation after giving +1 on the RC.
The WAL compression feature causes OOME and causes Full GC.

The problem is, if we have 1500 regions and I need to create recovered.edits
for each of the region (I don’t have much data in the regions (~300MB)).
Now when I try to build the dictionary there is a Node object getting
Each node object occupies 32 bytes.
We have 5 such dictionaries.

Initially we create indexToNodes array and its size is 32767.

So now we have 32*5*32767 = ~5MB.

Now I have 1500 regions.

So 5MB*1500 = ~7GB.(Excluding actual data).  This seems to a very high
initial memory foot print and this never allows me to split the logs and I
am not able to make the cluster up at all.

Our configured heap size was 8GB, tested in 3 node cluster with 5000
regions, very less data( 1GB in hdfs cluster including replication), some
small data is spread evenly across all regions.

The formula is 32(Node object size)*5(No of dictionary)*32767(no of node

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