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Head Tail and Sample in DataStage

Head Tail and Sample

Head 

Head is a debug stage which picks top ‘n’  records from all the nodes  (or)Specific nodes.

 

Screenshot_51

 

  • Head 7 properties
  • Rows

All rows  (After skip)  = false

Number of rows (preparation) = 2

  • Available properties period preparation skip preparation
  • Partitions

All Partitions = True

Click on output 7Do the mapping 7Ok

 

In the output :-

Top 2 records will be displayed

[In Sequential file , if we load multiple files , then set

S.F 7properties àoptions 7 Keep file partitions = True]

Tail

Tail is a debug stage which picks bottom ‘n’ records from all nodes or specific nodes

  • Tail
  •  properties
  •  Rows

Number of rows (preparation) = 2

 

Partitions

  • All Partitions = false

Click on output mapping

 

Display last 2 records

Ex:- Suppose that we have 60 records and we need to display 30th record to 40th record.

Sol :  In Head 7 properties 7Set No. of row  (per partition) = 40

In Tail7Properties7Set No. of row  (per partition) = 10

 

Screenshot_52

 

Sample

Sample is also a debug stage , which operates in ‘2’ Modes

 

  1. Period 7 1 input and 1 output
  2. Percentage 7 1 input and 1 output

Period is interval of records if period = 2 , displays 2,4, 6,8,10……….

  • Sample

Properties

  • Options

Percent = ?

Out click number = ?

Sample mode – period /percent

If period 

Options

  • Period (per partition)  =2 7 output à Mapping 7 ok

If percent 

Since  it has multiple output it follows link ordering.

Screenshot_53

options

Percent = 50

Output link Number =

Percent = 25

Output link number =

Sample Mode = percent 7 Click on link ordering (To know the link label) 7

0       t2

1  ↔  t1

2    t3

Now assign these values accordingly in output – link number

     ↓

Click on output

     ↓

Perform the mapping  fx t1, t2, t3

     ↓

Ok

 

Peek :-  (Multipurpose)

Peek is a debug stage which can be used for

  • Send the records to the logs
  • Make the Source to Multiple copies (can be used as “copy” stage)
  • Used as STUB stage (place holder)

Log 7 Detailed info abt execute

 

Screenshot_1

 

 

S.F 7 load peek 7 we can view data here 7 

 Properties7

   ↓

No. of Records = 5  (per partition) (All the 5

   ↓

Records will be sent to the job log)7

   ↓

Peek Records output Mode = Job log7

   ↓

ok

 

7After Compilation and Run , Go to “Tool”

  • Tool

      ↓

Run Director

      ↓

Select the job

      ↓

Click on job log Symbol

  • In that we can see 3 types of colors

 

  1. Green – ok
  2. Red – Error
  3. Yellow – Warning

To clear the Warnings

Right click on Warning (or) double click 7 Warning   Message will be displayed 7Identify the Warning and try to Eliminate them

Note:-    “Missing” record delimiter “/r/n”  (one type of error) (it means Mismatch)

In which Cases, we have to put an  “Reject link” and capture the mismatched data

Message Handing

Right click on  Yellow Warning 7Add to Message Handler 7 Actions (Suppress / Demote) 7Add Ruler 7ok Warning get converted in to Information

Filtering :-

Job 7Right click 7filter (put the options)

7click on job name 7 we can see 5 records

 

Peek properties 

Rows  all the rows  (after skip)   = false                                         properties

Number of records  (per partition) = columns                         period (per partition)

Peek all input  columns = True partitions                                   Skip  (per partition)

All partition = true

Options

Peek Records output Mode == Joblog                 properties

(or) output                                                   Deli meter string

Show column Name = True

Ex:

  • Suppose we want to see the data at each stages then attach a peek

Stage to each Transformation :

 

Oracle — Sort 7 Transformation1 7Transformation 2 7Transformation 3 7Data set

                         ↓                      ↓                    ↓

Peek 1                                               peek 2                                        peek 3

 

  • To select only particular columns:-

Peek can  send data to logs, peek can also send required columns to the logs.

Screenshot_2

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For Ex:-  If we have an table will fields and 9 records, and wanted to display only 2 fields with 9 records.

Peek 7 properties 7 No. of Records = 4 (per partition) 7columns 7Input column to peek = c id , Input column to peek = State,Peek all input columns = false 7 ok

7After compile and Run Tools 7 Run Director 7Select job 7 log 7Event Detail window appears

Output :-  peek 1, 0 : cid 1 ,state AP

  1. If we want to display only records with out displaying column names

Columns

Show column Name = false

 

  1. Make the source to Multiple copies

 

Screenshot_3

 

 

 

7 Peek 7 properties 7 No. of Records = 5  7 peek Records output Mode = job log 7Go to “output” tab 7 Map the data (l1, l2, l3) 7 ok

7Compile and run the job Here peek Stage ads as copy stage and copies,The data as it  is to the 3 data sets.

If we set  peek Record output Mode = output , then

Screenshot_4

 

 

 

Peek 7 properties 7 No. of Records = 5 7 peek Record output Mode = output 7Output 7 Map the data 7 ok

 

  • When we set peek Record output Mode = output, then the peek output

That is 5 records will be displayed in one of the .ds file , and in other .ds file

All records will be displayed.

 

  • In Data set 3 7 view data 7 we can see 5 records ( that is peek dat a)

7Suppose the client needs only rejected, but not output, thenHere we use peek as output stage

 

Screenshot_5

 

  • Here peek is used as STUB Stage , a place holder to store the data.

For indepth understanding of DataStage click on

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Head Tail and Sample in DataStage
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