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From Ted Yu <yuzhih...@gmail.com>
Subject Re: Does 'online region merge' make regions unavailable for some time?
Date Wed, 21 Jan 2015 18:26:32 GMT
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 <
otis.gospodnetic@gmail.com> 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 <
> vladimir.tretyakov@sematext.com> 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.
> >
>

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