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From Stack <st...@duboce.net>
Subject Re: question on column families
Date Wed, 14 Nov 2018 16:40:27 GMT
On Tue, Nov 13, 2018 at 7:20 PM Antonio Si <antonio.si@gmail.com> wrote:

> Thanks Allan.
>
> Then, why is it a problem of having too many column families? If there are
> column
> families with no data, would that cause any issues?
>
> Thanks.
>
>
`We have this note in the refguide [1]. It is a bit stale though.

Each CF consumes at least some resources. Then flush can be dumb and flush
more than just the loaded memstores (making for many small files in HDFS
which in turn need compacting...). Do you see this phenomenon?

If careful when querying and writing, then the CFs can work autonomously
and you can do more than what the refguide bounds.

S

1. http://hbase.apache.org/book.html#number.of.cfs


> Antonio.
>
> On Tue, Nov 13, 2018 at 7:09 PM Allan Yang <allan163@apache.org> wrote:
>
> > No, Every column family has its own memstore. Each one is 128MB in your
> > case. When flushing, the flusher will choose those memstore who satisfy
> > certain conditions, so it is possible that not every column family(Store)
> > will flush the memstore.
> > Best Regards
> > Allan Yang
> >
> >
> > Antonio Si <antonio.si@gmail.com> 于2018年11月14日周三 上午7:34写道:
> >
> > > Hi,
> > >
> > > I would like to confirm my understand.
> > >
> > > Let's say I have 13 column families in a hbase table. 11 of those
> column
> > > families have no data, which 2 column families have large amount of
> data.
> > >
> > > My understanding is that the size of memstore, which is 128M in my env,
> > > will be shared across all column families even though there is no data
> in
> > > that column families. Is my understanding correct?
> > >
> > > Thanks in advance.
> > >
> > > Antonio.
> > >
> >
>

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