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From Keith Turner <>
Subject Re: HDFS vs Accumulo Performance
Date Mon, 05 Dec 2016 17:01:01 GMT

Nice test!  One possible reason for the difference is the
de-serialization, iterator, re-serialization cost incurred in the
tserver case.  But I am not sure if this is the cause.  For the HDFS
case blobs of serialized data are read from HDFS and shipped to the
client.  When you run the test what does the CPU utilization on the
tserver and client look like?

The seeks are caused by the fact that scanner fetches batches of data.
It needs to seek for each batch.   This batch size can be adjusted
with table.scan.max.memory[1].



On Mon, Dec 5, 2016 at 11:37 AM, Mario Pastorelli
<> wrote:
> We are trying to understand Accumulo performance to better plan our future
> products that use it and we noticed that the read speed of Accumulo tends to
> be way lower than what we would expect. We have a testing cluster with 4
> HDFS+Accumulo nodes and we ran some tests. We wrote two programs to write to
> HDFS and Accumulo and two programs to read/scan from HDFS and Accumulo the
> same number of records containing random bytes. We run all the programs from
> outside the cluster, on another node of the rack that doesn’t have HDFS nor
> Accumulo.
> We also wrote all the HDFS blocks and Accumulo tablets on the same machine
> of the cluster.
> First of all, we wrote 10M entries to HDFS were each entry was 50 bytes
> each. This resulted in 4 blocks on HDFS. Reading this records with a
> FSDataInputStream takes around 5.7 seconds with an average speed of around
> 90MB per second.
> Then we wrote 10M entries to HDFS where each entry has a row of 50 random
> bytes, no column and no value. Writing is as fast as writing to HDFS modulo
> the compaction that we run at the end. The generated table has 1 tablet and
> obviously 10M records all on the same cluster. We waited for the compaction
> to finish, then we opened a scanner without setting the range and we read
> all the records. This time, reading the data took around 20 seconds with
> average speed of 25MB/s and 500000 records/s together with ~500 seeks/s. We
> have two questions about this result:
> 1 - is this kind of performance expected?
> 2 - Is there any configuration that we can change to improve the scan speed?
> 3 - why there are 500 seeks if there is only one tablet and we read
> sequentially all its bytes? What are those seeks doing?
> We tried to use a BatchScanner with 1, 5 and 10 threads but the speed was
> the same or even worse in some cases.
> I can provide the code that we used as well as information about our cluster
> configuration if you want.
> Thanks,
> Mario
> --
> Mario Pastorelli | TERALYTICS
> software engineer
> Teralytics AG | Zollstrasse 62 | 8005 Zurich | Switzerland
> phone: +41794381682
> email:
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> Zurich
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