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From Dave Revell <d...@urbanairship.com>
Subject Re: Restrictions during compactions
Date Wed, 23 May 2012 16:57:10 GMT
On Wed, May 23, 2012 at 6:15 AM, Takahiko Kawasaki <
takahiko.kawasaki@jibemobile.jp> wrote:

> Hello,
>
> I'm a newbie and wondering whether or not there is any restriction during
> HBase minor/major compactions. I read the online document but could not
> find any explicit mention about restrictions. What I'm mostly worrying
> about is whether read/write operations are blocked during compactions.
>
> The description about 'hbase.hstore.blockingWaitTime':
>
> ---
> The time an HRegion will block updates for after hitting the StoreFile
> limit defined by hbase.hstore.blockingStoreFiles. After this time has
> elapsed, the HRegion will stop blocking updates even if a compaction has
> not been completed. Default: 90 seconds.
> ---
>
> implies that updates are blocked during compactions, but at the same time
> it says that there are cases where blocking updates is stopped even if a
> compaction has not been completed. However, does it mean that the
> compaction is aborted or that the compaction continues and updates are
> performed successfully? And if the latter case is true, what is the reason
> to block updates during compactions? I'm confused.
>

That's not quite true. No operations are blocked during compactions. The
config value you're referring to is a kind of safety valve to prevent high
write throughput from overwhelming HBase's ability to compact. In the
normal case, you shouldn't have to worry about that config value until you
have very high write traffic.

So, short answer: clients can operate normally during compactions.

Best,
Dave

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