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From Eric Newton <eric.new...@gmail.com>
Subject Re: BatchScanner taking too much time to scan rows
Date Wed, 13 May 2015 17:28:20 GMT
Yes, that's a great way to split the data evenly.

Also, since the data set is so small, turn on data caching for your table:

shell> config -t mytable -s table.cache.block.enable=true

You may want to increase the size of your tserver JVM, and increase the
size of the cache:

shell> config -s tserver.cache.data.size=1G

This will help with repeated random look-ups.

-Eric

On Wed, May 13, 2015 at 11:31 AM, vaibhav thapliyal <
vaibhav.thapliyal.91@gmail.com> wrote:

> Thank you Eric.
>
> One thing I would like to know. Does pre-splitting the data play a part in
> querying accumulo?
>
> Because I managed to somewhat decrease the querying time.
> I did the following steps:
> My table was around 1.47gb so I explicity set the split parameter to 256mb
> instead of the default 1gb.
>
> So I had just 8 tablets. Now when I carried out the same query, it
> finished in 15s.
>
> Is it because of the split points are more evenly distributed?
>
> The previous table on which the query took 50s had entries unevenly
> distributed across the tablets.
> Thanks
> Vaibhav
> On 13-May-2015 7:43 pm, "Eric Newton" <eric.newton@gmail.com> wrote:
>
>> This use case is one of the things Accumulo was designed to handle well.
>> It's the reason there is a BatchScanner.
>>
>> I've created:
>>
>> https://issues.apache.org/jira/browse/ACCUMULO-3813
>>
>> so we can investigate and track down any problems or improvements.
>>
>> Feel free to add any other details to the JIRA ticket.
>>
>> -Eric
>>
>>
>> On Wed, May 13, 2015 at 10:03 AM, Emilio Lahr-Vivaz <elahrvivaz@ccri.com>
>> wrote:
>>
>>>  It sounds like each of your ranges is an ID, e.g. a single row. I've
>>> found that scanning lots of non-sequential single-row ranges is pretty slow
>>> in accumulo. Your best approach is probably to create an index table on
>>> whatever you are originally trying to query (assuming those 10000 ids came
>>> from some other query).
>>>
>>> Thanks,
>>>
>>> Emilio
>>>
>>>
>>> On 05/13/2015 09:14 AM, vaibhav thapliyal wrote:
>>>
>>>  The rf files per tablet vary between 2 to 5 per tablet. The entries
>>> returned to me by the batchScanner is 460000. The approx. average data rate
>>> is 0.5 MB/s as seen on the accumulo monitor page.
>>>
>>>  A simple scan on the table has an average data rate of about 7-8 MB/s.
>>>
>>>  All the ids exist in the accumulo table.
>>>
>>> On 12 May 2015 at 23:39, Keith Turner <keith@deenlo.com> wrote:
>>>
>>>> Do you know how much data is being brought back (i.e. 100 megabytes)? I
>>>> am wondering what the data rate is in MB/s.  Do you know how many files per
>>>> tablet you have?  Do most of the 10,000 ids you are querying for exist?
>>>>
>>>> On Tue, May 12, 2015 at 1:58 PM, vaibhav thapliyal <
>>>> vaibhav.thapliyal.91@gmail.com> wrote:
>>>>
>>>>> I have 194 tablets. Currently I am using 20 threads to create the
>>>>> batchscanner inside the createBatchScanner method.
>>>>>  On 12-May-2015 11:19 pm, "Keith Turner" <keith@deenlo.com> wrote:
>>>>>
>>>>>>   How many tablets do you have?  The batch scanner does not
>>>>>> parallelize operations within a tablet.
>>>>>>
>>>>>>  If you give the batch scanner more threads than there are tservers,
>>>>>> it will make multilple parallel rpc calls to each tserver if the
tserver
>>>>>> has multiple tablets.  Each rpc may include multiple tablets and
ranges for
>>>>>> each tablet.
>>>>>>
>>>>>>  If the batch scanner has less threads than tservers, it will make
>>>>>> one rpc per tserver per thread.  Each rpc call will include all tablets
and
>>>>>> associated ranges for that tserver.
>>>>>>
>>>>>>  Keith
>>>>>>
>>>>>>
>>>>>>
>>>>>> On Tue, May 12, 2015 at 1:39 PM, vaibhav thapliyal <
>>>>>> vaibhav.thapliyal.91@gmail.com> wrote:
>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>>  I am using BatchScanner to scan rows from a accumulo table.
The
>>>>>>> table has around 187m entries and I am using a 3 node cluster
which has
>>>>>>> accumulo 1.6.1.
>>>>>>>
>>>>>>>  I have passed 10000 ids which are stored as row id in my table
as
>>>>>>> a list in the setRanges() method.
>>>>>>>
>>>>>>>  This whole process takes around 50 secs(from adding the ids
in the
>>>>>>> list to scanning the whole table using the BatchScanner).
>>>>>>>
>>>>>>>  I tried switching on bloom filters but that didn't work.
>>>>>>>
>>>>>>>  Also if anyone could briefly explain how a BatchScanner works,
how
>>>>>>> it does parallel scanning it would help me understand what I
am doing
>>>>>>> better.
>>>>>>>
>>>>>>>  Thanks
>>>>>>>  Vaibhav
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>
>>>
>>>
>>

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