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From John Vines <>
Subject Re: Performance of table with large number of column families
Date Fri, 09 Nov 2012 18:09:49 GMT
Glad to hear. I typically advice a minimum of 2 shards per tserver. I would
say the maximum is actually based on the tablet size. Others in the country
may disagree/provide better reasoning.

Sent from my phone, pardon the typos and brevity.
On Nov 9, 2012 1:03 PM, "Anthony Fox" <> wrote:

> Ok, I reingested with 1000 rows and performance for both single record
> scans and index scans is much better.  I'm going to experiment a bit with
> the optimal number of rows.  Thanks for the help, everyone.
> On Fri, Nov 9, 2012 at 12:41 PM, John Vines <> wrote:
>> The bloom filter checks only occur on a seek, and the way the column
>> family filter works it's it seeks and then does a few scans to see if the
>> appropriate families pop up in the short term. Bloom filter on the column
>> family would be better if you had larger rows to encourage more
>> seeks/minimize the number of rows to do bloom checks.
>> The issue is that you are ultimately checking every single row for a
>> column, which is sparse. It's not that different than doing a full table
>> regex. If you had locality groups set up it would be more performant, until
>> you create locality groups for everything.
>> The intersecting iterators get their performance by being able to operate
>> on large rows to avoid the penalty of checking each row. Minimize the
>> number of partitions you have and it should clear up your issues.
>> John
>> Sent from my phone, pardon the typos and brevity.
>> On Nov 9, 2012 12:24 PM, "William Slacum" <>
>> wrote:
>>> I'll ask for someone to verify this comment for me (look @ u John W
>>> Vines), but the bloom filter helps when you have a discrete number of
>>> column families that will appear across many rows.
>>> On Fri, Nov 9, 2012 at 12:18 PM, Anthony Fox <>wrote:
>>>> Ah, ok, I was under the impression that this would be really fast since
>>>> I have a column family bloom filter turned on.  Is this not correct?
>>>> On Fri, Nov 9, 2012 at 12:15 PM, William Slacum <
>>>>> wrote:
>>>>> When I said smaller of tablets, I really mean smaller number of rows
>>>>> :) My apologies.
>>>>> So if you're searching for a random column family in a table, like
>>>>> with a `scan -c <cf>` in the shell, it will start at row 0 and
>>>>> sequentially up to row 10000000 until it finds the cf.
>>>>> On Fri, Nov 9, 2012 at 12:11 PM, Anthony Fox <>wrote:
>>>>>> This scan is without the intersecting iterator.  I'm just trying
>>>>>> pull back a single data record at the moment which corresponds to
>>>>>> for one column family.  I'll try with a smaller number of tablets,
but is
>>>>>> the computation effort the same for the scan I am doing?
>>>>>> On Fri, Nov 9, 2012 at 12:02 PM, William Slacum <
>>>>>>> wrote:
>>>>>>> So that means you have roughly 312.5k rows per tablet, which
>>>>>>> about 725k column families in any given tablet. The intersecting
>>>>>>> will work at a row per time, so I think at any given moment,
it will be
>>>>>>> working through 32 at a time and doing a linear scan through
the RFile
>>>>>>> blocks. With RFile indices, that check is usually pretty fast,
but you're
>>>>>>> having go through 4 orders of magnitude more data sequentially
than you can
>>>>>>> work on. If you can experiment and re-ingest with a smaller number
>>>>>>> tablets, anywhere between 15 and 45, I think you will see better
>>>>>>> performance.
>>>>>>> On Fri, Nov 9, 2012 at 11:53 AM, Anthony Fox <>wrote:
>>>>>>>> Failed to answer the original question - 15 tablet servers,
>>>>>>>> tablets/splits.
>>>>>>>> On Fri, Nov 9, 2012 at 11:52 AM, Anthony Fox <>wrote:
>>>>>>>>> I've tried a number of different settings of
>>>>>>>>> table.split.threshold.  I started at 1G and bumped it
down to 128M and the
>>>>>>>>> cf scan is still ~30 seconds for both.  I've also used
less rows - 00000 to
>>>>>>>>> 99999 and still see similar performance numbers.  I thought
the column
>>>>>>>>> family bloom filter would help deal with large row space
but sparsely
>>>>>>>>> populated column space.  Is that correct?
>>>>>>>>> On Fri, Nov 9, 2012 at 11:49 AM, William Slacum <
>>>>>>>>>> wrote:
>>>>>>>>>> I'm more inclined to believe it's because you have
to search
>>>>>>>>>> across 10M different rows to find any given column
family, since they're
>>>>>>>>>> randomly, and possibly uniformly, distributed. How
many tablets are you
>>>>>>>>>> searching across?
>>>>>>>>>> On Fri, Nov 9, 2012 at 11:45 AM, Anthony Fox <
>>>>>>>>>>> wrote:
>>>>>>>>>>> Yes, there are 10M possible partitions.  I do
not have a hash
>>>>>>>>>>> from value to partition, the data is essentially
randomly balanced across
>>>>>>>>>>> all the tablets.  Unlike the bloom filter and
intersecting iterator
>>>>>>>>>>> examples, I do not have locality groups turned
on and I have data in the cq
>>>>>>>>>>> and the value for both index entries and record
entries.  Could this be the
>>>>>>>>>>> issue?  Each record entry has approximately 30
column qualifiers with data
>>>>>>>>>>> in the value for each.
>>>>>>>>>>> On Fri, Nov 9, 2012 at 11:41 AM, William Slacum
>>>>>>>>>>>> wrote:
>>>>>>>>>>>> I guess assuming you have 10M possible partitions,
if you're
>>>>>>>>>>>> using a relatively uniform hash to generate
your IDs, you'll average about
>>>>>>>>>>>> 2 per partition. Do you have any index for
term/value to partition? This
>>>>>>>>>>>> will help you narrow down your search space
to a subset of your partitions.
>>>>>>>>>>>> On Fri, Nov 9, 2012 at 11:39 AM, William
Slacum <
>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>> That shouldn't be a huge issue. How many
rows/partitions do
>>>>>>>>>>>>> you have? How many do you have to scan
to find the specific column
>>>>>>>>>>>>> family/doc id you want?
>>>>>>>>>>>>> On Fri, Nov 9, 2012 at 11:26 AM, Anthony
Fox <
>>>>>>>>>>>>>> wrote:
>>>>>>>>>>>>>> I have a table set up to use the
intersecting iterator pattern.  The
>>>>>>>>>>>>>> table has about 20M records which
leads to 20M column families for the
>>>>>>>>>>>>>> data section - 1 unique column family
per record.  The index section of
>>>>>>>>>>>>>> the table is not quite as large as
the data section.  The rowkey is a
>>>>>>>>>>>>>> random padded integer partition between
0000000 and 9999999.  I turned
>>>>>>>>>>>>>> bloom filters on and used the ColumnFamilyFunctor
to get performant
>>>>>>>>>>>>>> column family scans without specifying
a range like in the bloom filter
>>>>>>>>>>>>>> examples in the README.  However,
my column family scans (without any
>>>>>>>>>>>>>> custom iterator) are still fairly
slow - ~30 seconds for a column family
>>>>>>>>>>>>>> batch scan of one record. I've also
tried RowFunctor but I see similar
>>>>>>>>>>>>>> performance.  Can anyone shed any
light on the performance metrics I'm
>>>>>>>>>>>>>> seeing?
>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>> Anthony

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