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Posted to user@hbase.apache.org by Mohit Anchlia <mo...@gmail.com> on 2012/08/01 20:41:17 UTC
Region server failure question
I was reading blog
http://www.cloudera.com/blog/2012/07/hbase-log-splitting/ and
it looks like if region servers fails then all the regions on that region
servers are unavailable until a regions are assigned to a different region
server. Does it mean all the key ranges for the failed region server is
unavailable for reads and writes until regions are available on some other
region server? If so then how to deal with failures while real time data
might be flowing into HBase.
Re: Region server failure question
Posted by Lars George <la...@gmail.com>.
That is correct, the client blocks and retries a configurable amount of time until the regions are available again.
Lars
On Aug 2, 2012, at 7:01 AM, Mohit Anchlia <mo...@gmail.com> wrote:
> On Wed, Aug 1, 2012 at 12:52 PM, Mohammad Tariq <do...@gmail.com> wrote:
>
>> Hello Mohit,
>>
>> If replication factor is set to some value > 1, then the data is
>> still present on some other node(perhaps within the same rack or a
>> different one). And, as far as this post is concerned it tells us
>> about Write Ahead Logs, i.e data that is still not written onto the
>> disk. This is different from the data written in HFiles, i.e the
>> persistent data. If the regionserver fails while the data is still
>> being written, the data can be recovered by replaying the edits from
>> the WAL file. Please let me know if you disagree.
>>
>>
> I understand that there is no data loss. However, it looks like that all
> the regions on specific region server is unavailable until it comes back
> up? It looks like that all client read and write calls for those key ranges
> would fail until new region server split the logs and bring the regions up.
>
>
>> Regards,
>> Mohammad Tariq
>>
>>
>> On Thu, Aug 2, 2012 at 12:11 AM, Mohit Anchlia <mo...@gmail.com>
>> wrote:
>>> I was reading blog
>>> http://www.cloudera.com/blog/2012/07/hbase-log-splitting/ and
>>> it looks like if region servers fails then all the regions on that region
>>> servers are unavailable until a regions are assigned to a different
>> region
>>> server. Does it mean all the key ranges for the failed region server is
>>> unavailable for reads and writes until regions are available on some
>> other
>>> region server? If so then how to deal with failures while real time data
>>> might be flowing into HBase.
>>
Re: Region server failure question
Posted by Mohit Anchlia <mo...@gmail.com>.
On Wed, Aug 1, 2012 at 12:52 PM, Mohammad Tariq <do...@gmail.com> wrote:
> Hello Mohit,
>
> If replication factor is set to some value > 1, then the data is
> still present on some other node(perhaps within the same rack or a
> different one). And, as far as this post is concerned it tells us
> about Write Ahead Logs, i.e data that is still not written onto the
> disk. This is different from the data written in HFiles, i.e the
> persistent data. If the regionserver fails while the data is still
> being written, the data can be recovered by replaying the edits from
> the WAL file. Please let me know if you disagree.
>
>
I understand that there is no data loss. However, it looks like that all
the regions on specific region server is unavailable until it comes back
up? It looks like that all client read and write calls for those key ranges
would fail until new region server split the logs and bring the regions up.
> Regards,
> Mohammad Tariq
>
>
> On Thu, Aug 2, 2012 at 12:11 AM, Mohit Anchlia <mo...@gmail.com>
> wrote:
> > I was reading blog
> > http://www.cloudera.com/blog/2012/07/hbase-log-splitting/ and
> > it looks like if region servers fails then all the regions on that region
> > servers are unavailable until a regions are assigned to a different
> region
> > server. Does it mean all the key ranges for the failed region server is
> > unavailable for reads and writes until regions are available on some
> other
> > region server? If so then how to deal with failures while real time data
> > might be flowing into HBase.
>
Re: Region server failure question
Posted by Mohammad Tariq <do...@gmail.com>.
Hello Mohit,
If replication factor is set to some value > 1, then the data is
still present on some other node(perhaps within the same rack or a
different one). And, as far as this post is concerned it tells us
about Write Ahead Logs, i.e data that is still not written onto the
disk. This is different from the data written in HFiles, i.e the
persistent data. If the regionserver fails while the data is still
being written, the data can be recovered by replaying the edits from
the WAL file. Please let me know if you disagree.
Regards,
Mohammad Tariq
On Thu, Aug 2, 2012 at 12:11 AM, Mohit Anchlia <mo...@gmail.com> wrote:
> I was reading blog
> http://www.cloudera.com/blog/2012/07/hbase-log-splitting/ and
> it looks like if region servers fails then all the regions on that region
> servers are unavailable until a regions are assigned to a different region
> server. Does it mean all the key ranges for the failed region server is
> unavailable for reads and writes until regions are available on some other
> region server? If so then how to deal with failures while real time data
> might be flowing into HBase.