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From Vladimir Rodionov <vladrodio...@gmail.com>
Subject Re: optimal size for Hbase.hregion.memstore.flush.size and its impact
Date Mon, 24 Aug 2015 17:23:55 GMT
1. How many regions per RS?
2. What is your dfs.block.size?
3. What is your hbase.regionserver.maxlogs?

Flush can be requested when:

1. Region size exceeds hbase.hregion.memstore.flush.size
2. Region's memstore is too old (periodic memstore flusher checks the age
of memstore, default is 1hour) Controlled by
    hbase.regionserver.optionalcacheflushinterval (in ms)
3. There too many unflushed changes in a Region. Controlled by
hbase.regionserver.flush.per.changes, default is 30,000,000
4. WAL is rolling prematurely, controlled by   hbase.regionserver.maxlogs
and  dfs.block.size.

You calculate optimal: hbase.regionserver.maxlogs * dfs.block.size * 0.95 >
hbase.regionserver.global.memstore.upperLimit  * HBASE_HEAPSIZE

I recommend you to enable DEBUG logging and analyze MemStoreFlusher,
PeriodicMemstoreFlusher and HRegion flush related log messages to get idea
why flush was requested on a region(s), what was the region size at that
time.

I think, in your case it is either premature WAL rolling or too many
changes in a memstore.

-Vlad


On Wed, May 27, 2015 at 1:53 PM, Gautam Borah <gautam.borah@gmail.com>
wrote:

> Hi all,
>
> The default size of Hbase.hregion.memstore.flush.size is define as 128 MB
> for Hbase.hregion.memstore.flush.size. Could anyone kindly explain what
> would be the impact if we increase this to a higher value 512 MB or 800 MB
> or higher.
>
> We have a very write heavy cluster. Also we run periodic end point co
> processor based jobs that operate on the data written in the last 10-15
> mins, every 10 minute. We are trying to manage the memstore flush
> operations such that the hot data remains in memstore for at least 30-40
> mins or longer, so that the job hits disk every 3rd or 4th time it tries to
> operate on the hot data (it does scan).
>
> We have region server heap size of 20 GB and set the,
>
> hbase.regionserver.global.memstore.lowerLimit = .45
> hbase.regionserver.global.memstore.upperLimit = .55
>
> We observed that if we set the Hbase.hregion.memstore.flush.size=128MB
> only 10% of the heap is utilized by memstore, after that memstore flushes.
>
> At Hbase.hregion.memstore.flush.size=512MB, we are able to increase the
> heap utelization to by memstore to 35%.
>
> It would be very helpful for us to understand the implication of higher
> Hbase.hregion.memstore.flush.size  for a long running cluster.
>
> Thanks,
> Gautam

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