Re: Re:Re: Re: Optimize Order By + Limit Query

[Lu Cao]

@Liang, Yes, actually I'm currently working on the limit query
optimization.
I get the limited dictionary value and convert to the filter condition in
CarbonOptimizer step.
It would definitely improve the query performance in some scenario.

On Thu, Mar 30, 2017 at 2:07 PM, Liang Chen  wrote:

> Hi
>
> +1 for simafengyun's optimization, it looks good to me.
>
> I propose to do "limit" pushdown first, similar with filter pushdown. what
> is your opionion? @simafengyun
>
> For "order by" pushdown, let us work out an ideal solution to consider all
> aggregation push down cases. Ravindara's comment is reasonable, we need to
> consider decoupling spark and carbondata, otherwise maintenance cost might
> be high if do computing works at both side, because we need to keep
> utilizing Spark' computing capability along with its version evolution.
>
> Regards
> Liang
>
>
> simafengyun wrote
> > Hi Ravindran,
> > yes, use carbon do the sorting if the order by column is not first
> > column.But its sorting is very high since the dimension data in blocklet
> > is stored after sorting.So in carbon can use  merge sort  + topN to get N
> > data from each block.In addition,  the biggest difference is that it can
> > reduce disk IO since can use limit n to reduce required blocklets.if you
> > only apply spark's top N, I don't think you can make  suck below
> > performance. That's impossible  if don't reduce disk IO.
> >
>  n5.nabble.com/file/n9834/%E6%9C%AA%E5%91%BD%E5%90%8D2.jpg>
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > At 2017-03-30 03:12:54, "Ravindra Pesala" ravi.pes...@gmail.com
> > wrote:
> >>Hi,
> >>
> >>You mean Carbon do the sorting if the order by column is not first column
> >>and provide only limit values to spark. But the same job spark is also
> >>doing it just sorts the partition and gets the top values out of it. You
> >>can reduce the table_blocksize to get the better sort performance as
> spark
> >>try to do sorting inside memory.
> >>
> >>I can see we can do some optimizations in integration layer itself with
> out
> >>pushing down any logic to carbon like if the order by column is first
> >>column then we can just get limit values with out sorting any data.
> >>
> >>Regards,
> >>Ravindra.
> >>
> >>On 29 March 2017 at 08:58, 马云 simafengyun1...@163.com wrote:
> >>
> >>> Hi Ravindran,
> >>> Thanks for your quick response. please see my answer as below
> >>> 
> >>>  What if the order by column is not the first column? It needs to scan
> >>> all
> >>> blocklets to get the data out of it if the order by column is not first
> >>> column of mdk
> >>> 
> >>> Answer :  if step2 doesn't filter any blocklet, you are right,It needs
> >>> to
> >>> scan all blocklets to get the data out of it if the order by column is
> >>> not
> >>> first column of mdk
> >>> but it just scan all the order by column's data, for
> >>> others columns data,  use the lazy-load strategy and  it can reduce
> scan
> >>> accordingly to  limit value.
> >>> Hence you can see the performance is much better now
> >>> after  my optimization. Currently the carbondata order by + limit
> >>> performance is very bad since it scans all data.
> >>>in my test there are  20,000,000 data, it takes more
> than
> >>> 10s, if data is much more huge,  I think it is hard for user to stand
> >>> such
> >>> bad performance when they do order by + limit  query?
> >>>
> >>>
> >>> 
> >>>  We used to have multiple push down optimizations from spark to carbon
> >>> like aggregation, limit, topn etc. But later it was removed because it
> >>> is
> >>> very hard to maintain for version to version. I feel it is better that
> >>> execution engine like spark can do these type of operations.
> >>> 
> >>> Answer : In my opinion, I don't think "hard to maintain for version to
> >>> version" is a good reason to give up the order by  + limit
> optimization.
> >>> I think it can create new class to extends current and try to reduce
> the
> >>> impact for the current code. Maybe can make it is easy to maintain.
> >>> Maybe I am wrong.
> >>>
> >>>
> >>>
> >>>
> >>> At 2017-03-29 02:21:58, "Ravindra Pesala" ravi.pes...@gmail.com
> 
> >>> wrote:
> >>>
> >>>
> >>> Hi Jarck Ma,
> >>>
> >>> It is great to try optimizing Carbondata.
> >>> I think this solution comes up with many limitations. What if the order
> >>> by
> >>> column is not the first column? It needs to scan all blocklets to get
> >>> the
> >>> data out of it if the order by column is not first column of mdk.
> >>>
> >>> We used to have multiple push down optimizations from spark to carbon
> >>> like
> >>> aggregation, limit, topn etc. But later it was removed because it is
> >>> very
> >>> 

Re: Re: Optimize Order By + Limit Query

[simafengyun]

add images for my last post


1. about how to work for dictionary columns and guarantee to get a sort
result
*Answer:*  As I know the dictionary allocation is in sorted order  in block
level, even in segment level, not in global level.
But that's enough, please see the below example about how to get the correct
sort result


 

2.about how to reduce io


 



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Nabble.com.

Re:Re: Re: Re: Optimize Order By + Limit Query

[马云]

Hi, 
Please see my answer.

1. It cannot work for dictionary columns. As there is no guarantee that 
dictionary allocation is in sorted order. 


Answer:  As I know the dictionary allocation is in sorted order  in block 
level, even in segment level, not in global level.
But that's enough, please see the below example about how to get the correct 
sort result

2. It cannot work for no inverted index columns. 


Answer: One question, by default if user didn't configure a dimension column 
with no inverted index when create table.
But after data loading, it has no inverted index in deed. in this case, is it 
still  in sorted order  in blocklet(or datachunk2) level? 
if yes,  it's physical row id should equals the logical row id, of cause it is 
not necessary to create  inverted index.
Hence by default the solution should work for this kind of case.

3. It cannot work for measures. 

Answer: yes, you are right, can't support with measure column since it is not  
in sorted order 

Moreover as you mentioned that it can reduce IO, But I don't think we can 
reduce any IO since we need to read all blocklets to do merge sort. And I 
am not sure how we can keep all the data in memory until we do merge sort. 


Answer: we don't need to load all selected columns' data in memory.
only need to load all the order by column' data in memory. others columns can 
use lazy-loading.
We also can set a orderby-optimization flag, if user think they have not too 
much memory, can switch it to off.
about reduce io, there are 2 ways.
1. sort blocklets according to the orderby dimensions' min(or max) values.
then according to limit value to get the required blocklet for scan. 
2. reduce the io for non order by" columns data since they 


I am still believe that this work is belonged to execution engine, not file 
format. This type of specific improvements may give good performance in 
some specific type of queries but these will give long term complications 
in maintainability. 








At 2017-03-30 11:58:06, "Ravindra Pesala"  wrote:
>Hi,
>
>It comes up with many limitations
>1. It cannot work for dictionary columns. As there is no guarantee that
>dictionary allocation is in sorted order.
>2. It cannot work for no inverted index columns.
>3. It cannot work for measures.
>
>Moreover as you mentioned that it can reduce IO, But I don't think we can
>reduce any IO since we need to read all blocklets to do merge sort. And I
>am not sure how we can keep all the data in memory until we do merge sort.
>I am still believe that this work is belonged to execution engine, not file
>format. This type of specific improvements may give good performance in
>some specific type of queries but these will give long term complications
>in maintainability.
>
>
>Regards,
>Ravindra.
>
>On 30 March 2017 at 08:23, 马云  wrote:
>
>> Hi Ravindran,
>>
>> yes, use carbon do the sorting if the order by column is not first column.
>>
>> But its sorting is very high since the dimension data in blocklet is stored 
>> after sorting.
>>
>> So in carbon can use  merge sort  + topN to get N data from each block.
>>
>> In addition,  the biggest difference is that it can reduce disk IO since can 
>> use limit n to reduce required blocklets.
>>
>> if you only apply spark's top N, I don't think you can make  suck below 
>> performance.
>>
>> That's impossible  if don't reduce disk IO.
>>
>>
>>
>>
>>
>>
>>
>>
>> At 2017-03-30 03:12:54, "Ravindra Pesala"  wrote:
>> >Hi,
>> >
>> >You mean Carbon do the sorting if the order by column is not first column
>> >and provide only limit values to spark. But the same job spark is also
>> >doing it just sorts the partition and gets the top values out of it. You
>> >can reduce the table_blocksize to get the better sort performance as spark
>> >try to do sorting inside memory.
>> >
>> >I can see we can do some optimizations in integration layer itself with out
>> >pushing down any logic to carbon like if the order by column is first
>> >column then we can just get limit values with out sorting any data.
>> >
>> >Regards,
>> >Ravindra.
>> >
>> >On 29 March 2017 at 08:58, 马云  wrote:
>> >
>> >> Hi Ravindran,
>> >> Thanks for your quick response. please see my answer as below
>> >> 
>> >>  What if the order by column is not the first column? It needs to scan all
>> >> blocklets to get the data out of it if the order by column is not first
>> >> column of mdk
>> >> 
>> >> Answer :  if step2 doesn't filter any blocklet, you are right,It needs to
>> >> scan all blocklets to get the data out of it if the order by column is not
>> >> first column of mdk
>> >> but it just scan all the order by column's data, for
>> >> others columns data,  use the lazy-load strategy and  it can reduce scan
>> >> accordingly to  limit value.
>> >>

Re: Re:Re: Re: Optimize Order By + Limit Query

[Liang Chen]

Hi

+1 for simafengyun's optimization, it looks good to me.

I propose to do "limit" pushdown first, similar with filter pushdown. what
is your opionion? @simafengyun

For "order by" pushdown, let us work out an ideal solution to consider all
aggregation push down cases. Ravindara's comment is reasonable, we need to
consider decoupling spark and carbondata, otherwise maintenance cost might
be high if do computing works at both side, because we need to keep
utilizing Spark' computing capability along with its version evolution.

Regards
Liang


simafengyun wrote
> Hi Ravindran,
> yes, use carbon do the sorting if the order by column is not first
> column.But its sorting is very high since the dimension data in blocklet
> is stored after sorting.So in carbon can use  merge sort  + topN to get N
> data from each block.In addition,  the biggest difference is that it can
> reduce disk IO since can use limit n to reduce required blocklets.if you
> only apply spark's top N, I don't think you can make  suck below
> performance. That's impossible  if don't reduce disk IO.
> 

 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> At 2017-03-30 03:12:54, "Ravindra Pesala" ravi.pes...@gmail.com
> wrote:
>>Hi,
>>
>>You mean Carbon do the sorting if the order by column is not first column
>>and provide only limit values to spark. But the same job spark is also
>>doing it just sorts the partition and gets the top values out of it. You
>>can reduce the table_blocksize to get the better sort performance as spark
>>try to do sorting inside memory.
>>
>>I can see we can do some optimizations in integration layer itself with
out
>>pushing down any logic to carbon like if the order by column is first
>>column then we can just get limit values with out sorting any data.
>>
>>Regards,
>>Ravindra.
>>
>>On 29 March 2017 at 08:58, 马云 simafengyun1...@163.com wrote:
>>
>>> Hi Ravindran,
>>> Thanks for your quick response. please see my answer as below
>>> 
>>>  What if the order by column is not the first column? It needs to scan
>>> all
>>> blocklets to get the data out of it if the order by column is not first
>>> column of mdk
>>> 
>>> Answer :  if step2 doesn't filter any blocklet, you are right,It needs
>>> to
>>> scan all blocklets to get the data out of it if the order by column is
>>> not
>>> first column of mdk
>>> but it just scan all the order by column's data, for
>>> others columns data,  use the lazy-load strategy and  it can reduce scan
>>> accordingly to  limit value.
>>> Hence you can see the performance is much better now
>>> after  my optimization. Currently the carbondata order by + limit
>>> performance is very bad since it scans all data.
>>>in my test there are  20,000,000 data, it takes more than
>>> 10s, if data is much more huge,  I think it is hard for user to stand
>>> such
>>> bad performance when they do order by + limit  query?
>>>
>>>
>>> 
>>>  We used to have multiple push down optimizations from spark to carbon
>>> like aggregation, limit, topn etc. But later it was removed because it
>>> is
>>> very hard to maintain for version to version. I feel it is better that
>>> execution engine like spark can do these type of operations.
>>> 
>>> Answer : In my opinion, I don't think "hard to maintain for version to
>>> version" is a good reason to give up the order by  + limit optimization.
>>> I think it can create new class to extends current and try to reduce the
>>> impact for the current code. Maybe can make it is easy to maintain.
>>> Maybe I am wrong.
>>>
>>>
>>>
>>>
>>> At 2017-03-29 02:21:58, "Ravindra Pesala" ravi.pes...@gmail.com
>>> wrote:
>>>
>>>
>>> Hi Jarck Ma,
>>>
>>> It is great to try optimizing Carbondata.
>>> I think this solution comes up with many limitations. What if the order
>>> by
>>> column is not the first column? It needs to scan all blocklets to get
>>> the
>>> data out of it if the order by column is not first column of mdk.
>>>
>>> We used to have multiple push down optimizations from spark to carbon
>>> like
>>> aggregation, limit, topn etc. But later it was removed because it is
>>> very
>>> hard to maintain for version to version. I feel it is better that
>>> execution
>>> engine like spark can do these type of operations.
>>>
>>>
>>> Regards,
>>> Ravindra.
>>>
>>>
>>>
>>> On Tue, Mar 28, 2017, 14:28 马云 simafengyun1...@163.com wrote:
>>>
>>>
>>> Hi Carbon Dev,
>>>
>>> Currently I have done optimization for ordering by 1 dimension.
>>>
>>> my local performance test as below. Please give your suggestion.
>>>
>>>
>>>
>>>
>>> | data count | test sql | limit value in sql | performance(ms) |
>>> | optimized code | original code |
>>> | 

Re: Re: Re: Optimize Order By + Limit Query

[Ravindra Pesala]

Hi,

It comes up with many limitations
1. It cannot work for dictionary columns. As there is no guarantee that
dictionary allocation is in sorted order.
2. It cannot work for no inverted index columns.
3. It cannot work for measures.

Moreover as you mentioned that it can reduce IO, But I don't think we can
reduce any IO since we need to read all blocklets to do merge sort. And I
am not sure how we can keep all the data in memory until we do merge sort.
I am still believe that this work is belonged to execution engine, not file
format. This type of specific improvements may give good performance in
some specific type of queries but these will give long term complications
in maintainability.


Regards,
Ravindra.

On 30 March 2017 at 08:23, 马云  wrote:

> Hi Ravindran,
>
> yes, use carbon do the sorting if the order by column is not first column.
>
> But its sorting is very high since the dimension data in blocklet is stored 
> after sorting.
>
> So in carbon can use  merge sort  + topN to get N data from each block.
>
> In addition,  the biggest difference is that it can reduce disk IO since can 
> use limit n to reduce required blocklets.
>
> if you only apply spark's top N, I don't think you can make  suck below 
> performance.
>
> That's impossible  if don't reduce disk IO.
>
>
>
>
>
>
>
>
> At 2017-03-30 03:12:54, "Ravindra Pesala"  wrote:
> >Hi,
> >
> >You mean Carbon do the sorting if the order by column is not first column
> >and provide only limit values to spark. But the same job spark is also
> >doing it just sorts the partition and gets the top values out of it. You
> >can reduce the table_blocksize to get the better sort performance as spark
> >try to do sorting inside memory.
> >
> >I can see we can do some optimizations in integration layer itself with out
> >pushing down any logic to carbon like if the order by column is first
> >column then we can just get limit values with out sorting any data.
> >
> >Regards,
> >Ravindra.
> >
> >On 29 March 2017 at 08:58, 马云  wrote:
> >
> >> Hi Ravindran,
> >> Thanks for your quick response. please see my answer as below
> >> 
> >>  What if the order by column is not the first column? It needs to scan all
> >> blocklets to get the data out of it if the order by column is not first
> >> column of mdk
> >> 
> >> Answer :  if step2 doesn't filter any blocklet, you are right,It needs to
> >> scan all blocklets to get the data out of it if the order by column is not
> >> first column of mdk
> >> but it just scan all the order by column's data, for
> >> others columns data,  use the lazy-load strategy and  it can reduce scan
> >> accordingly to  limit value.
> >> Hence you can see the performance is much better now
> >> after  my optimization. Currently the carbondata order by + limit
> >> performance is very bad since it scans all data.
> >>in my test there are  20,000,000 data, it takes more than
> >> 10s, if data is much more huge,  I think it is hard for user to stand such
> >> bad performance when they do order by + limit  query?
> >>
> >>
> >> 
> >>  We used to have multiple push down optimizations from spark to carbon
> >> like aggregation, limit, topn etc. But later it was removed because it is
> >> very hard to maintain for version to version. I feel it is better that
> >> execution engine like spark can do these type of operations.
> >> 
> >> Answer : In my opinion, I don't think "hard to maintain for version to
> >> version" is a good reason to give up the order by  + limit optimization.
> >> I think it can create new class to extends current and try to reduce the
> >> impact for the current code. Maybe can make it is easy to maintain.
> >> Maybe I am wrong.
> >>
> >>
> >>
> >>
> >> At 2017-03-29 02:21:58, "Ravindra Pesala"  wrote:
> >>
> >>
> >> Hi Jarck Ma,
> >>
> >> It is great to try optimizing Carbondata.
> >> I think this solution comes up with many limitations. What if the order by
> >> column is not the first column? It needs to scan all blocklets to get the
> >> data out of it if the order by column is not first column of mdk.
> >>
> >> We used to have multiple push down optimizations from spark to carbon like
> >> aggregation, limit, topn etc. But later it was removed because it is very
> >> hard to maintain for version to version. I feel it is better that execution
> >> engine like spark can do these type of operations.
> >>
> >>
> >> Regards,
> >> Ravindra.
> >>
> >>
> >>
> >> On Tue, Mar 28, 2017, 14:28 马云  wrote:
> >>
> >>
> >> Hi Carbon Dev,
> >>
> >> Currently I have done optimization for ordering by 1 dimension.
> >>
> >> my local performance test as below. Please 

Re:Re: Re: Optimize Order By + Limit Query

[马云]

Hi Ravindran,yes, use carbon do the sorting if the order by column is not first 
column.But its sorting is very high since the dimension data in blocklet is 
stored after sorting.So in carbon can use  merge sort  + topN to get N data 
from each block.In addition,  the biggest difference is that it can reduce disk 
IO since can use limit n to reduce required blocklets.if you only apply spark's 
top N, I don't think you can make  suck below performance. That's impossible  
if don't reduce disk IO.












At 2017-03-30 03:12:54, "Ravindra Pesala"  wrote:
>Hi,
>
>You mean Carbon do the sorting if the order by column is not first column
>and provide only limit values to spark. But the same job spark is also
>doing it just sorts the partition and gets the top values out of it. You
>can reduce the table_blocksize to get the better sort performance as spark
>try to do sorting inside memory.
>
>I can see we can do some optimizations in integration layer itself with out
>pushing down any logic to carbon like if the order by column is first
>column then we can just get limit values with out sorting any data.
>
>Regards,
>Ravindra.
>
>On 29 March 2017 at 08:58, 马云  wrote:
>
>> Hi Ravindran,
>> Thanks for your quick response. please see my answer as below
>> 
>>  What if the order by column is not the first column? It needs to scan all
>> blocklets to get the data out of it if the order by column is not first
>> column of mdk
>> 
>> Answer :  if step2 doesn't filter any blocklet, you are right,It needs to
>> scan all blocklets to get the data out of it if the order by column is not
>> first column of mdk
>> but it just scan all the order by column's data, for
>> others columns data,  use the lazy-load strategy and  it can reduce scan
>> accordingly to  limit value.
>> Hence you can see the performance is much better now
>> after  my optimization. Currently the carbondata order by + limit
>> performance is very bad since it scans all data.
>>in my test there are  20,000,000 data, it takes more than
>> 10s, if data is much more huge,  I think it is hard for user to stand such
>> bad performance when they do order by + limit  query?
>>
>>
>> 
>>  We used to have multiple push down optimizations from spark to carbon
>> like aggregation, limit, topn etc. But later it was removed because it is
>> very hard to maintain for version to version. I feel it is better that
>> execution engine like spark can do these type of operations.
>> 
>> Answer : In my opinion, I don't think "hard to maintain for version to
>> version" is a good reason to give up the order by  + limit optimization.
>> I think it can create new class to extends current and try to reduce the
>> impact for the current code. Maybe can make it is easy to maintain.
>> Maybe I am wrong.
>>
>>
>>
>>
>> At 2017-03-29 02:21:58, "Ravindra Pesala"  wrote:
>>
>>
>> Hi Jarck Ma,
>>
>> It is great to try optimizing Carbondata.
>> I think this solution comes up with many limitations. What if the order by
>> column is not the first column? It needs to scan all blocklets to get the
>> data out of it if the order by column is not first column of mdk.
>>
>> We used to have multiple push down optimizations from spark to carbon like
>> aggregation, limit, topn etc. But later it was removed because it is very
>> hard to maintain for version to version. I feel it is better that execution
>> engine like spark can do these type of operations.
>>
>>
>> Regards,
>> Ravindra.
>>
>>
>>
>> On Tue, Mar 28, 2017, 14:28 马云  wrote:
>>
>>
>> Hi Carbon Dev,
>>
>> Currently I have done optimization for ordering by 1 dimension.
>>
>> my local performance test as below. Please give your suggestion.
>>
>>
>>
>>
>> | data count | test sql | limit value in sql | performance(ms) |
>> | optimized code | original code |
>> | 20,000,000 | SELECT name, serialname, country, salary, id, date FROM t3
>> ORDER BY country limit 1000 | 1000 | 677 | 10906 |
>> | SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
>> serialname limit 1 | 1 | 1897 | 12108 |
>> | SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
>> serialname limit 5 | 5 | 2814 | 14279 |
>>
>> my optimization solution for order by 1 dimension ＋ limit as below
>>
>> mainly filter some unnecessary blocklets and leverage  the dimension's
>> order stored feature to get sorted data in each partition.
>>
>> at last use the TakeOrderedAndProject to merge sorted data from partitions
>>
>> step1. change logical plan and push down the order by and limit
>> information to carbon scan
>>
>> and change sort physical plan to TakeOrderedAndProject  

Re: Re: Optimize Order By + Limit Query

[Ravindra Pesala]

Hi,

You mean Carbon do the sorting if the order by column is not first column
and provide only limit values to spark. But the same job spark is also
doing it just sorts the partition and gets the top values out of it. You
can reduce the table_blocksize to get the better sort performance as spark
try to do sorting inside memory.

I can see we can do some optimizations in integration layer itself with out
pushing down any logic to carbon like if the order by column is first
column then we can just get limit values with out sorting any data.

Regards,
Ravindra.

On 29 March 2017 at 08:58, 马云  wrote:

> Hi Ravindran,
> Thanks for your quick response. please see my answer as below
> 
>  What if the order by column is not the first column? It needs to scan all
> blocklets to get the data out of it if the order by column is not first
> column of mdk
> 
> Answer :  if step2 doesn't filter any blocklet, you are right,It needs to
> scan all blocklets to get the data out of it if the order by column is not
> first column of mdk
> but it just scan all the order by column's data, for
> others columns data,  use the lazy-load strategy and  it can reduce scan
> accordingly to  limit value.
> Hence you can see the performance is much better now
> after  my optimization. Currently the carbondata order by + limit
> performance is very bad since it scans all data.
>in my test there are  20,000,000 data, it takes more than
> 10s, if data is much more huge,  I think it is hard for user to stand such
> bad performance when they do order by + limit  query?
>
>
> 
>  We used to have multiple push down optimizations from spark to carbon
> like aggregation, limit, topn etc. But later it was removed because it is
> very hard to maintain for version to version. I feel it is better that
> execution engine like spark can do these type of operations.
> 
> Answer : In my opinion, I don't think "hard to maintain for version to
> version" is a good reason to give up the order by  + limit optimization.
> I think it can create new class to extends current and try to reduce the
> impact for the current code. Maybe can make it is easy to maintain.
> Maybe I am wrong.
>
>
>
>
> At 2017-03-29 02:21:58, "Ravindra Pesala"  wrote:
>
>
> Hi Jarck Ma,
>
> It is great to try optimizing Carbondata.
> I think this solution comes up with many limitations. What if the order by
> column is not the first column? It needs to scan all blocklets to get the
> data out of it if the order by column is not first column of mdk.
>
> We used to have multiple push down optimizations from spark to carbon like
> aggregation, limit, topn etc. But later it was removed because it is very
> hard to maintain for version to version. I feel it is better that execution
> engine like spark can do these type of operations.
>
>
> Regards,
> Ravindra.
>
>
>
> On Tue, Mar 28, 2017, 14:28 马云  wrote:
>
>
> Hi Carbon Dev,
>
> Currently I have done optimization for ordering by 1 dimension.
>
> my local performance test as below. Please give your suggestion.
>
>
>
>
> | data count | test sql | limit value in sql | performance(ms) |
> | optimized code | original code |
> | 20,000,000 | SELECT name, serialname, country, salary, id, date FROM t3
> ORDER BY country limit 1000 | 1000 | 677 | 10906 |
> | SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
> serialname limit 1 | 1 | 1897 | 12108 |
> | SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
> serialname limit 5 | 5 | 2814 | 14279 |
>
> my optimization solution for order by 1 dimension ＋ limit as below
>
> mainly filter some unnecessary blocklets and leverage  the dimension's
> order stored feature to get sorted data in each partition.
>
> at last use the TakeOrderedAndProject to merge sorted data from partitions
>
> step1. change logical plan and push down the order by and limit
> information to carbon scan
>
> and change sort physical plan to TakeOrderedAndProject  since
> data will be get and sorted in each partition
>
> step2. in each partition apply the limit number, blocklet's min_max index
> to filter blocklet.
>
>   it can reduce scan data if some blocklets were filtered
>
>  for example,  SELECT name, serialname, country, salary, id, date
> FROM t3 ORDER BY serialname limit 1
>
>  supposing there are 2 blocklets , each has 32000 data, serial name  is
> between serialname1 to serialname2 in the first blocklet
>
> and between  serialname2 to serialname3 in the second blocklet. Actually
> we only need to scan the first blocklet
>
> since 32000 > 100 and first blocklet's serial name <= second blocklet's
> serial name
>
>
>
> 

Re: Optimize Order By + Limit Query

[Ravindra Pesala]

Hi Jarck Ma,

It is great to try optimizing Carbondata.
I think this solution comes up with many limitations. What if the order by
column is not the first column? It needs to scan all blocklets to get the
data out of it if the order by column is not first column of mdk.

We used to have multiple push down optimizations from spark to carbon like
aggregation, limit, topn etc. But later it was removed because it is very
hard to maintain for version to version. I feel it is better that execution
engine like spark can do these type of operations.

Regards,
Ravindra.

On Tue, Mar 28, 2017, 14:28 马云  wrote:

> Hi Carbon Dev,
>
> Currently I have done optimization for ordering by 1 dimension.
>
> my local performance test as below. Please give your suggestion.
>
>
> data count test sql limit value in sql performance(ms)
> optimized code original code
> 20,000,000 SELECT name, serialname, country, salary, id, date FROM t3
> ORDER BY country limit 1000 1000 677 10906
> SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
> serialname limit 1 1 1897 12108
> SELECT name, serialname, country, salary, id, date FROM t3 ORDER BY
> serialname limit 5 5 2814 14279
>
> my optimization solution for order by 1 dimension ＋ limit as below
>
> mainly filter some unnecessary blocklets and leverage  the dimension's
> order stored feature to get sorted data in each partition.
>
> at last use the TakeOrderedAndProject to merge sorted data from partitions
>
> *step1*. change logical plan and push down the order by and limit
> information to carbon scan
>
> and change sort physical plan to TakeOrderedAndProject  since
> data will be get and sorted in each partition
>
> *step2*. in each partition apply the limit number, blocklet's min_max
> index to filter blocklet.
>
>   it can reduce scan data if some blocklets were filtered
>
>  for example,  SELECT name, serialname, country, salary, id, date
> FROM t3 ORDER BY serialname limit 1
>
>  supposing there are 2 blocklets , each has 32000 data, serial name  is
> between serialname1 to serialname2 in the first blocklet
>
> and between  serialname2 to serialname3 in the second blocklet. Actually
> we only need to scan the first blocklet
>
> since 32000 > 100 and first blocklet's serial name <= second
> blocklet's serial name
>
>
>
> *step3*.  load the order by dimension data to scanResult.  put all
> scanResults to a TreeSet for sorting
>
>   Other columns' data will be lazy-loaded in step4.
>
> *step4.* according to the limit value, use a iterator to get the topN
> sorted data from the TreeSet. In the same time to load other columns data
> if needed.
>
>in this step  it tries to reduce scanning non-sort dimension
>  data.
>
>  for example, SELECT name, serialname, country, salary, id, date
> FROM t3 ORDER BY serialname limit 1
>
>  supposing there are 3 blocklets ,  in the first 2 blocklets, serial name
>  is between serialname1 to serialname100 and each has 2500 serialname1
> and serialname2.
>
> In the third blocklet, serial name
>  is between serialname2 to serialnam100, but no serialname1 in it.
>
> load serial name data for the 3 blocklets and put all to a treeset
> sorting by the min serialname.
>
> apparently use iterator to get the top 1 sorted data, it only need to
> care the first 2 blocklets(5000 serialname1 + 5000 serialname2).
>
> In others words, it  loads serial name data for the 3 blocklets.But only
> "load name, country, salary, id, date"'s data for the first 2 blocklets
>
>
>
> *step5.* TakeOrderedAndProject physical plan will be used to merge sorted
> data from partitions
>
>
>
> the below items also can be optimized in future
>
>
>
> •   *leverage *mdk keys' order feature to optimize the SQL who order by
> prefix dimension columns of MDK
>
> •   use the dimension order feature in blocklet lever and dimensions'
> inverted index to optimize SQL who order by multi-dimensions
>
>
>
>
>
>
>
>
>
>
>
> Jarck Ma
>
>
>
>
>
>