Please take a look at slides 5 and 6 in this file: https://issues.apache.org/jira/secure/attachment/12561887/merge%20region.pdf
It is clear that the two regions to be merged are taken offline in step 1. Cheers On Tue, Jan 20, 2015 at 5:26 PM, Otis Gospodnetic < [email protected]> wrote: > Hi, > > Considering this is called the *online* region merge, I would assume > regions being merged never go offline during the merge and both regions > being merged are available for reading and writing at all times, even > during the merge.... though I don't get how writes would work if one region > is being moved from one RS to another.... so maybe this is not truly online > and writes are either rejected or buffered/blocked until the region is > moved AND merged? Anyone knows for sure? > > I see this in one of the comments: > Q: If one (or both) of the regions were receiving non-trivial load prior to > this action, would client(s) be affected ? > A: Yes, region would be off services in a short time, it is equal with > moving region, e.g balance a region > > Also took a look at the patch: > > https://issues.apache.org/jira/secure/attachment/12574965/hbase-7403-trunkv33.patch > > And see: > > + /** > + * The merging region A has been taken out of the server's online > regions list. > + */ > + OFFLINED_REGION_A, > > > ... and if you look for the word "offline" in the patch I think it's > pretty clear that BOTH regions being merged do go offline at some > point. I guess it could be after the merge, too, not before.... > > ... maybe others know? > > > Thanks, > Otis > -- > Monitoring * Alerting * Anomaly Detection * Centralized Log Management > Solr & Elasticsearch Support * http://sematext.com/ > > > On Mon, Jan 19, 2015 at 4:17 AM, Vladimir Tretyakov < > [email protected]> wrote: > > > Hi, I have one question about 'online region merge' ( > > https://issues.apache.org/jira/browse/HBASE-7403). > > How I've understood regions which will be passed to merge method will be > > unavailable for some time. > > > > That means: > > 1. Some data will be unavailable some time. > > 2. If client will try to write data to these regions it will get > > exceptions. > > > > Are above sentences correct? > > > > Somebody can estimate time which 1 and 2 will be true? Seconds, minutes > or > > hours? Is there any way to avoid 1 and 2? > > > > I am asking because now we have problem during time with number of > regions > > (our key contains timestamp), count of regions growing constantly > > (splitting) and it become a cause of performance problem with time. > > For avoiding this effect we use 2 tables: > > 1. First table we use for writing and reading data. > > 2. Second we use only for reading data. > > > > After some time we truncate second table and rotate these tables (first > > become second and second become first). That allow us control count of > > regions, but solution looks a bit ugly, I looked at 'online region > merge', > > but we can't live with restrictions I've described in first part of > > question. > > > > Can somebody help with answers? > > > > Thx, Vladimir Tretyakov. > > >
