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From DuyHai Doan <doanduy...@gmail.com>
Subject Re: Why does Cassandra need to have 2B column limit? why can't we have unlimited ?
Date Sat, 15 Oct 2016 11:38:47 GMT
Yes, more or less. The 100Mb is a rule of thumb. No one will blame you for
storing 200Mb for example. The figure is just given as an example of order
of magnitude

On Sat, Oct 15, 2016 at 1:37 PM, Kant Kodali <kant@peernova.com> wrote:

> you mean 100MB (MegaBytes)? Also the data in each of my column is about
> 1KB so in that case the optimal size 100K columns (since 100K * 1KB =
> 100MB) right?
>
> On Sat, Oct 15, 2016 at 4:26 AM, DuyHai Doan <doanduyhai@gmail.com> wrote:
>
>> "2) so what is optimal limit in terms of data size?"
>>
>> --> Usual recommendations for Cassandra 2.1 are:
>>
>> a. max 100Mb per partition size
>> b. or up to 10 000 000 physical columns for a partition (including
>> clustering columns etc ...)
>>
>> Recently, with the work of Robert Stupp (CASSANDRA-11206) and also with
>> the huge enhancement from Michael Kjellman (CASSANDRA-9754) it will be
>> easier to handle huge partition in memory, especially with a reduce memory
>> footprint with regards to the JVM heap.
>>
>> However, as long as we don't have repair and streaming processes that can
>> be "resumed" in a middle of a partition, the operational pains will still
>> be there. Same for compaction
>>
>>
>>
>> On Sat, Oct 15, 2016 at 12:00 PM, Kant Kodali <kant@peernova.com> wrote:
>>
>>> 1) It will be great if someone can confirm that there is no limit
>>> 2) so what is optimal limit in terms of data size?
>>>
>>> Finally, Thanks a lot for pointing out all the operational issues!
>>>
>>> On Sat, Oct 15, 2016 at 2:39 AM, DuyHai Doan <doanduyhai@gmail.com>
>>> wrote:
>>>
>>>> "But is there still 2B columns limit on the Cassandra code?"
>>>>
>>>> --> I remember some one the committer saying that this 2B columns
>>>> limitation comes from the Thrift era where you're limited to max  2B
>>>> columns to be returned to the client for each request. It also applies to
>>>> the max size of each "page" of data
>>>>
>>>> Since the introduction of the binary protocol and the paging feature,
>>>> this limitation does not make sense anymore.
>>>>
>>>> By the way, if your partition is too wide, you'll face other
>>>> operational issues way before reaching the 2B columns limit:
>>>>
>>>> - compaction taking looooong time --> heap pressure --> long GC pauses
>>>> --> nodes flapping
>>>> - repair & over-streaming, repair session failure in the middle that
>>>> forces you to re-send the whole big partition --> the receiving node has
a
>>>> bunch of duplicate data --> pressure on compaction
>>>> - bootstrapping of new nodes --> failure to stream a partition in the
>>>> middle will force to re-send the whole partition from the beginning again
-->
>>>> the receiving node has a bunch of duplicate data --> pressure on compaction
>>>>
>>>>
>>>>
>>>> On Sat, Oct 15, 2016 at 9:15 AM, Kant Kodali <kant@peernova.com> wrote:
>>>>
>>>>>  compacting 10 sstables each of them have a 15GB partition in what
>>>>> duration?
>>>>>
>>>>> On Fri, Oct 14, 2016 at 11:45 PM, Matope Ono <matope.ono@gmail.com>
>>>>> wrote:
>>>>>
>>>>>> Please forget the part in my sentence.
>>>>>> For more correctly, maybe I should have said like "He could compact
>>>>>> 10 sstables each of them have a 15GB partition".
>>>>>> What I wanted to say is we can store much more rows(and columns)
in a
>>>>>> partition than before 3.6.
>>>>>>
>>>>>> 2016-10-15 15:34 GMT+09:00 Kant Kodali <kant@peernova.com>:
>>>>>>
>>>>>>> "Robert said he could treat safely 10 15GB partitions at his
>>>>>>> presentation" This sounds like there is there is a row limit
too
>>>>>>> not only columns??
>>>>>>>
>>>>>>> If I am reading this correctly 10 15GB partitions  means 10
>>>>>>> partitions (like 10 row keys,  thats too small) with each partition
of size
>>>>>>> 15GB. (thats like 15 million columns where each column can have
a data of
>>>>>>> size 1KB).
>>>>>>>
>>>>>>> On Fri, Oct 14, 2016 at 11:30 PM, Kant Kodali <kant@peernova.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> "Robert said he could treat safely 10 15GB partitions at
his
>>>>>>>> presentation" This sounds like there is there is a row limit
too
>>>>>>>> not only columns??
>>>>>>>>
>>>>>>>> If I am reading this correctly 10 15GB partitions  means
10
>>>>>>>> partitions (like 10 row keys,  thats too small) with each
partition of size
>>>>>>>> 15GB. (thats like 10 million columns where each column can
have a data of
>>>>>>>> size 1KB).
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>>
>>>>>>>> On Fri, Oct 14, 2016 at 9:54 PM, Matope Ono <matope.ono@gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Thanks to CASSANDRA-11206, I think we can have much larger
>>>>>>>>> partition than before 3.6.
>>>>>>>>> (Robert said he could treat safely 10 15GB partitions
at his
>>>>>>>>> presentation. https://www.youtube.com/watch?v=N3mGxgnUiRY)
>>>>>>>>>
>>>>>>>>> But is there still 2B columns limit on the Cassandra
code?
>>>>>>>>> If so, out of curiosity, I'd like to know where the bottleneck
is.
>>>>>>>>> Could anyone let me know about it?
>>>>>>>>>
>>>>>>>>> Thanks Yasuharu.
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> 2016-10-13 1:11 GMT+09:00 Edward Capriolo <edlinuxguru@gmail.com>:
>>>>>>>>>
>>>>>>>>>> The "2 billion column limit" press clipping "puffery".
This
>>>>>>>>>> statement seemingly became popular because highly
traffic traffic-ed story,
>>>>>>>>>> in which a tech reporter embellished on a statement
to make a splashy
>>>>>>>>>> article.
>>>>>>>>>>
>>>>>>>>>> The effect is something like this:
>>>>>>>>>> http://www.healthnewsreview.org/2012/08/iced-tea-kidney-ston
>>>>>>>>>> es-and-the-study-that-never-existed/
>>>>>>>>>>
>>>>>>>>>> Iced tea does not cause kidney stones! Cassandra
does not store
>>>>>>>>>> rows with 2 billion columns! It is just not true.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> On Wed, Oct 12, 2016 at 4:57 AM, Kant Kodali <kant@peernova.com>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> Well 1) I have not sent it to postgresql mailing
lists 2) I
>>>>>>>>>>> thought this is an open ended question as it
can involve ideas from
>>>>>>>>>>> everywhere including the Cassandra java driver
mailing lists so sorry If
>>>>>>>>>>> that bothered you for some reason.
>>>>>>>>>>>
>>>>>>>>>>> On Wed, Oct 12, 2016 at 1:41 AM, Dorian Hoxha
<
>>>>>>>>>>> dorian.hoxha@gmail.com> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> Also, I'm not sure, but I don't think it's
"cool" to write to
>>>>>>>>>>>> multiple lists in the same message. (based
on postgresql mailing lists
>>>>>>>>>>>> rules).
>>>>>>>>>>>> Example I'm not subscribed to those, and
now the messages are
>>>>>>>>>>>> separated.
>>>>>>>>>>>>
>>>>>>>>>>>> On Wed, Oct 12, 2016 at 10:37 AM, Dorian
Hoxha <
>>>>>>>>>>>> dorian.hoxha@gmail.com> wrote:
>>>>>>>>>>>>
>>>>>>>>>>>>> There are some issues working on larger
partitions.
>>>>>>>>>>>>> Hbase doesn't do what you say! You have
also to be carefull on
>>>>>>>>>>>>> hbase not to create large rows! But since
they are globally-sorted, you can
>>>>>>>>>>>>> easily sort between them and create small
rows.
>>>>>>>>>>>>>
>>>>>>>>>>>>> In my opinion, cassandra people are wrong,
in that they say
>>>>>>>>>>>>> "globally sorted is the devil!" while
all fb/google/etc actually use
>>>>>>>>>>>>> globally-sorted most of the time! You
have to be careful though (just like
>>>>>>>>>>>>> with random partition)
>>>>>>>>>>>>>
>>>>>>>>>>>>> Can you tell what rowkey1, page1, col(x)
actually are ? Maybe
>>>>>>>>>>>>> there is a way.
>>>>>>>>>>>>> The most "recent", means there's a timestamp
in there ?
>>>>>>>>>>>>>
>>>>>>>>>>>>> On Wed, Oct 12, 2016 at 9:58 AM, Kant
Kodali <
>>>>>>>>>>>>> kant@peernova.com> wrote:
>>>>>>>>>>>>>
>>>>>>>>>>>>>> Hi All,
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I understand Cassandra can have a
maximum of 2B rows per
>>>>>>>>>>>>>> partition but in practice some people
seem to suggest the magic number is
>>>>>>>>>>>>>> 100K. why not create another partition/rowkey
automatically (whenever we
>>>>>>>>>>>>>> reach a safe limit that  we consider
would be efficient)  with auto
>>>>>>>>>>>>>> increment bigint  as a suffix appended
to the new rowkey? so that the
>>>>>>>>>>>>>> driver can return the new rowkey
 indicating that there is a new partition
>>>>>>>>>>>>>> and so on...Now I understand this
would involve allowing partial row key
>>>>>>>>>>>>>> searches which currently Cassandra
wouldn't do (but I believe HBASE does)
>>>>>>>>>>>>>> and thinking about token ranges and
potentially many other things..
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> My current problem is this
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> I have a row key followed by bunch
of columns (this is not
>>>>>>>>>>>>>> time series data)
>>>>>>>>>>>>>> and these columns can grow to any
number so since I have 100K
>>>>>>>>>>>>>> limit (or whatever the number is.
say some limit) I want to break the
>>>>>>>>>>>>>> partition into level/pages
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> rowkey1, page1->col1, col2, col3......
>>>>>>>>>>>>>> rowkey1, page2->col1, col2, col3......
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> now say my Cassandra db is populated
with data and say my
>>>>>>>>>>>>>> application just got booted up and
I want to most recent value of a certain
>>>>>>>>>>>>>> partition but I don't know which
page it belongs to since my application
>>>>>>>>>>>>>> just got booted up? how do I solve
this in the most efficient that is
>>>>>>>>>>>>>> possible in Cassandra today? I understand
I can create MV, other tables
>>>>>>>>>>>>>> that can hold some auxiliary data
such as number of pages per partition and
>>>>>>>>>>>>>> so on..but that involves the maintenance
cost of that other table which I
>>>>>>>>>>>>>> cannot afford really because I have
MV's, secondary indexes for other good
>>>>>>>>>>>>>> reasons. so it would be great if
someone can explain the best way possible
>>>>>>>>>>>>>> as of today with Cassandra? By best
way I mean is it possible with one
>>>>>>>>>>>>>> request? If Yes, then how? If not,
then what is the next best way to solve
>>>>>>>>>>>>>> this?
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> Thanks,
>>>>>>>>>>>>>> kant
>>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>>
>>>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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