Hi Qiao


Optimizer picked 6 as DOP. You can force it higher:



Use

CQD parallel_num_esps ‘12’;

Then prepare and run the query.



You may experiment with re-generating you table with SALT 15 and CQD
parallel_num_esps ‘15’.



you can even draw a curve

SALT 18, parallel_num_esp ‘18’

SALT  21, parallel_num_esps ‘21’

Etc 3 by 3 until you see that performance stop getting better, and actually
drops.



I see you did not change VARCHAR to CHAR and did not use Charset ISO88591:
this is important to optimize row size. UTF8 is very greedy specially for
PK columns. When I see your sample sid, I wonder if you really need UTF8.



Same principle apply for the other columns, but less important than for key.



Ultimately you can change the default value of HBASE_OPTIONS BLOCKSIZE

Default is 65565, you can try doubling or quadrupling it. This will improve
scan rate but crease any query that does random access.



Also I checked in an experimental feature to allow scanning in parallel
without using ESP (using multithreading instead), in case memory resource
consumed by ESP becomes a bottleneck, but I would not recommend it yet as
it is “experimental” still…

Except if you start seeing memory pressure…

Hope this helps,
Eric









*From:* 乔彦克 [mailto:qya...@gmail.com]
*Sent:* Monday, September 19, 2016 11:38 PM
*To:* u...@trafodion.incubator.apache.org
*Cc:* dev <dev@trafodion.incubator.apache.org>; Eric Owhadi <
eric.owh...@esgyn.com>; Qifan Chen <qifan.c...@esgyn.com>
*Subject:* Re: trafodion query optimization



Many thanks  to Eric and Qifan again.

I upload a new log about the new ddl and the query plan.

@Eric, Following your advice I modified the ddl, the sum query now takes
25seconds while the old ddl will take 90seconds.(there are 3 nodes in my
cluster, 8cores(16 v-cores) and 16GRAM), Is there any other optimize
options to make the sum query more fast (better less than 10seconds)?

@Qifan, I log the output of showstats command in the attachment, looking
forward more suggestions.



Thanks again.

Qiao



Qifan Chen <qifan.c...@esgyn.com>于2016年9月19日周一 下午9:23写道:

Hi Qiao,



Thank you for the data. It is very helpful.



There are several things noticed.

   - The key columns are: _SALT_, _DIVISION_1_, SID, V_DATE, UID, VID
   - The salt column is built from column SID only, which means all rows
   with identical SID values V will be stored in the same partition.
   - From the query plan, the compiler assigns 6 executor processes (we
   call ESP) to read the salted table of 12 partitions: 1 ESP reads 2 salt
   partitions.
   - The frequency of V is high when sid='6b2a0957' (~8million rows), all
   these relevant rows are handled by one execution process out of 6. That
   probably is the reason of not much parallelism observed.
   - You can use SQL command *showstats with detail* option to check the
   frequency on column SID.


   - showstats for table TRAFODION.SEABASE.VISIT_FROM_HIVE2 on SID detail;


   - If high frequency per unique value on column SID is confirmed, we
   probably should consider our next step of action. For example, we could add
   some columns from the primary key to the SALT clause to help spread V of
   SID to all 12 partitions.

Could you please send us the output of the showstats command above, and the
showstats command below for all columns in the table?



showstats for table TRAFODION.SEABASE.VISIT_FROM_HIVE2 on every column;



Thanks --Qifan



On Mon, Sep 19, 2016 at 3:15 AM, 乔彦克 <qya...@gmail.com> wrote:

Thanks Eric and Qifan. I am sorry to reply after so long a time because I'm
on the Chinese mid-autumn festival holiday.

According to Qifan's advice, I upload a log which contains the DDL and the
query plan hope to get more advice.



and to Eric, I summit a jira about the block-encoding and the compression,
https://issues.apache.org/jira/browse/TRAFODION-2195, so I only use the
hbase compression.

Qifan Chen <qifan.c...@esgyn.com>于2016年9月12日周一 下午10:43写道:

Hi Qiao,



You can also send us the DDL and the query plan to help with the tuning.



To generate a query plan, do the following from sqlci, and the plan is in
text file mylog.



   1. log mylog clear;
   2. prepare xx from <your query>;
   3. explain xx;
   4. explain options 'f' xx;
   5. exit;



Thanks --Qifan



On Mon, Sep 12, 2016 at 8:21 AM, Eric Owhadi <eric.owh...@esgyn.com> wrote:

Hello Qiao,
When you say whatever the table ddl it limits things a lot, as table ddl
will help define several things that will drastically improve the degree of
parallelism and the table size.

The DOP (degree of parallelism) of the scan operator is constrained by the
number of regions your table uses. So if you want to increase DOP, you need
to partition your table using the syntax like:
create table customer_demographics_salt
(
 cd_demo_sk int not null
 , cd_gender char(1)
 , cd_marital_status char(1)
 , cd_education_status char(20)
 , cd_purchase_estimate int
 , cd_credit_rating char(10)
 , cd_dep_count int
 , cd_dep_employed_count int
 , cd_dep_college_count int
 , primary key (cd_demo_sk)
)
salt using 12 partitions
ATTRIBUTES ALIGNED FORMAT
HBASE_OPTIONS
  (
    DATA_BLOCK_ENCODING = 'FAST_DIFF',
    COMPRESSION = 'SNAPPY'
  );

you can experiment with different values of number of partitions (but pick a
multiple of 3 since you have 3 nodes).

Then the optimizer will pick the DOP with a compromise of resource usage vs
gain in speed.
If you want to force higher DOP than what optimizer selected, you can use :
CQD parallel_num_esps '12';
To force it to one ESP per partition (assuming you picked 12 partitions).
You can verify what optimizer picked as DOP by doing an explain on the
query.

Other important factors plays in performance:
- use of aligned format (see above example)
- careful choice of the primary key (bad idea to use a varchar with big max
size)
- It is good idea to use compression and encoding (see the most common
options we use above)
- you can also increase the HBASE_OPTIONS BLOCKSIZE parameter, but there is
a drawback: increasing it will increase performance of SCAN but decrease
performance of keyed access. That is why I did not include it in the example
above.

Hope this helps,
Regards,
Eric


-----Original Message-----
From: 乔彦克 [mailto:qya...@gmail.com]
Sent: Monday, September 12, 2016 1:22 AM
To: u...@trafodion.incubator.apache.org; dev@trafodion.incubator.apache.org
Subject: trafodion query optimization

Hi all,
     I executed the sum and count query on my table where the cluster has
three nodes. I found that the sum query is not well parallel executed(not
all the three nodes get high load when executing the sum query) and the cpu
load is very high while the memory load is very low(the machines have 16
cores and 16GB memory). My sum query on the 12 million data sets takes about
2 minutes and a half time.
    So my question is that is there any optimization advice that I can use
to improve the query performance and maximize the usage of my machines, what
ever the configuration or the table ddl.
    Any replies is appreciated.

Thanks,
Qiao





-- 

Regards, --Qifan







-- 

Regards, --Qifan

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