Wellington, I might be misinterpreting this: http://stackoverflow.com/questions/13741946/role-of-datanode-regionserver-in-hbase-hadoop-integration
But aren't HBase region servers and HDFS datanodes always in the same server? With a replication factor of 3, what happens if all 3 datanodes hosting that information go down and one of them come back, but with the disk intact? Considering from the time they went down to the time it went back HBase received new writes that would go to the same data node... From: [email protected] Subject: Re: write availability The data is stored on files on hdfs. If a RS goes down, the master knows which regions were on that RS and which hdfs files contain data for these regions, so it will just assign the regions to others RS, and these others RS will have access to the regions data because it's stored on HDFS. The RS does not "own" the disk, this is HDFS job, so the recovery on this case is transparent. On 7 Apr 2015, at 16:51, Marcelo Valle (BLOOMBERG/ LONDON) <[email protected]> wrote: > 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: [email protected] > 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) > <[email protected]> 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: [email protected] >> 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 <[email protected]> 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) < >>> [email protected]>: >>> >>>> 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 > >
