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Accumulo, mail # user - Performance of table with large number of column families


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Re: Performance of table with large number of column families
Anthony Fox 2012-11-09, 18:02
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 <[EMAIL PROTECTED]> 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" <[EMAIL PROTECTED]>
> 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 <[EMAIL PROTECTED]>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 <
>>> [EMAIL PROTECTED]> 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 work sequentially
>>>> up to row 10000000 until it finds the cf.
>>>>
>>>>
>>>> On Fri, Nov 9, 2012 at 12:11 PM, Anthony Fox <[EMAIL PROTECTED]>wrote:
>>>>
>>>>> This scan is without the intersecting iterator.  I'm just trying to
>>>>> pull back a single data record at the moment which corresponds to scanning
>>>>> 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 <
>>>>> [EMAIL PROTECTED]> wrote:
>>>>>
>>>>>> So that means you have roughly 312.5k rows per tablet, which means
>>>>>> about 725k column families in any given tablet. The intersecting iterator
>>>>>> 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 of
>>>>>> tablets, anywhere between 15 and 45, I think you will see better
>>>>>> performance.
>>>>>>
>>>>>> On Fri, Nov 9, 2012 at 11:53 AM, Anthony Fox <[EMAIL PROTECTED]>wrote:
>>>>>>
>>>>>>> Failed to answer the original question - 15 tablet servers, 32
>>>>>>> tablets/splits.
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Nov 9, 2012 at 11:52 AM, Anthony Fox <[EMAIL PROTECTED]>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?
>>>>>>>