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From "Marcelo Valle (BLOOMBERG/ LONDON)" <mvallemil...@bloomberg.net>
Subject Re: write availability
Date Tue, 07 Apr 2015 15:51:25 GMT
So if a RS goes down, it's assumed you lost the data on it, right?
HBase has replications on HDFS, so if a RS goes down it doesn't mean I lost all the data,
as I could have the replicas yet... But what happens if all RS hosting a specific region goes
down? 
What if one RS from this one comes back again, but with the disk intact, with all the data
it had before crashing?


From: user@hbase.apache.org 
Subject: Re: write availability

When a RS goes down, the Master will try to assign the regions on the remaining RSes. When
the RS comes back, after a while, the Master balancer process will re-distribute regions between
RS, so the given RS will be hosting regions, but not necessarily the one it used to host before
it went down.


On 7 Apr 2015, at 16:31, Marcelo Valle (BLOOMBERG/ LONDON) <mvallemilita@bloomberg.net>
wrote:

>> So if the cluster is up, then you can insert records in to HBase even though you
lost a RS that was handing a specific region. 
> 
> What happens when the RS goes down? Writes to that region will be written to another
region server? Another RS assumes the region "range" while the RS is down?
> 
> What happens when the RS that was down goes up again? 
> 
> 
> From: user@hbase.apache.org 
> Subject: Re: write availability
> 
> I don’t know if I would say that… 
> 
> I read Marcelo’s question of “if the cluster is up, even though a RS may be down,
can I still insert records in to HBase?”
> 
> So if the cluster is up, then you can insert records in to HBase even though you lost
a RS that was handing a specific region. 
> 
> But because he talked about syncing nodes… I could be misreading his initial question…

> 
>> On Apr 7, 2015, at 9:02 AM, Serega Sheypak <serega.sheypak@gmail.com> wrote:
>> 
>>> If I have an application that writes to a HBase cluster, can I count that
>> the cluster will always available to receive writes?
>> No, it's CP, not AP system.
>>> so everything get in sync when the other nodes get up again
>> There is no hinted backoff, It's not Cassandra.
>> 
>> 
>> 
>> 2015-04-07 14:48 GMT+02:00 Marcelo Valle (BLOOMBERG/ LONDON) <
>> mvallemilita@bloomberg.net>:
>> 
>>> If I have an application that writes to a HBase cluster, can I count that
>>> the cluster will always available to receive writes?
>>> I might not be able to read if a region server which handles a range of
>>> keys is down, but will I be able to keep writing to other nodes, so
>>> everything get in sync when the other nodes get up again?
>>> Or I might get no write availability for a while?
> 
> The opinions expressed here are mine, while they may reflect a cognitive thought, that
is purely accidental. 
> Use at your own risk. 
> Michael Segel
> michael_segel (AT) hotmail.com


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