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From lars hofhansl <lhofha...@yahoo.com>
Subject Re: HBase Cyclic Replication Issue: some data are missing in the replication for intensive write
Date Fri, 20 Apr 2012 19:34:44 GMT
Hi Jerry,

which version of HBase are you using?

You are not using cyclic backup, that needs >2 clusters. I assume you're just replicating
from one cluster to another, right?

There is never data loss in Cluster A?

-- Lars


----- Original Message -----
From: Jerry Lam <chilinglam@gmail.com>
To: user@hbase.apache.org
Cc: 
Sent: Friday, April 20, 2012 5:38 AM
Subject: HBase Cyclic Replication Issue: some data are missing in the replication for intensive
write

Hi HBase community:

We have been testing cyclic replication for 1 week. The basic functionality seems to work
as described in the document however when we started to increase the write workload, the replication
starts to miss data (i.e. some data are not replicated to the other cluster). We have narrowed
down to a scenario that we can reproduce the problem quite consistently and here it is:

-----------------------------
Setup:
- We have setup 2 clusters (cluster A and cluster B)with identical size in terms of number
of nodes and configuration, 3 regionservers sit on top of 3 datanodes. 
- Cyclic replication is enabled.

- We use YCSB to generate load to hbase the workload is very similar to workloada:

recordcount=200000
operationcount=200000
workload=com.yahoo.ycsb.workloads.CoreWorkload
fieldcount=1
fieldlength=25000

readallfields=true
writeallfields=true

readproportion=0
updateproportion=1
scanproportion=0
insertproportion=0

requestdistribution=uniform

- Records are inserted into Cluster A. After the benchmark is done and wait until all data
are replicated to Cluster B, we used verifyrep mapreduce job for validation.
- Data are deleted from both table (truncate 'tablename') before a new experiment is started.

Scenario:
when we increase the number of threads until it max out the throughput of the cluster, we
saw some data are missing in Cluster B (total count != 200000) although cluster A clearly
has them all. This happens even though we disabled region splitting in both clusters (it happens
more often when region splits occur). To further having more control of what is happening,
we then decided to disable the load balancer so the region (which is responsible for the replicating
data) will not relocate to other regionserver during the benchmark. The situation improves
a lot. We don't see any missing data in 5 continuous runs. Finally, we decided to move the
region around from a regionserver to another regionserver during the benchmark to see if the
problem will reappear and it did. 

We believe that the issue could be related to region splitting and load balancing during intensive
write, the hbase replication strategy hasn't yet cover those corner cases. 

Can someone take a look of it and suggest some ways to workaround this? 

Thanks~

Jerry 

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