Answer / venugopal [patni]

The 3 stages differ mainly in the memory they use,
treatment of rows with unmatched & their requirements for
data being input.
In detailed:
Lookup is used for less amount of data becausu it will
takes the data from source and store in buffer so every
time it process from buffer.
Join is used for huge amount of data because it directly
takes the data from disk so it process faster than lookup.
Joiner is used to join with different join conditions.
Merge is also used for huge amount of data. Merge has the
same number of reject links as there are updated updated
input links.

Answer / aishwarya

Join Stage:
1.) It has n input links(one being primary and remaining
being secondary links), one output link and there is no
reject link
2.) It has 4 join operations: inner join, left outer join,
right outer join and full outer join
3.) join occupies less memory, hence performance is high in
join stage
4.) Here default partitioning technique would be Hash
partitioning technique
5.) Prerequisite condition for join is that before
performing join operation, the data should be sorted.

Look up Stage:
1.) It has n input links, one output link and 1reject link
2.) It can perform only 2 join operations: inner join and
left outer join
3.) Join occupies more memory, hence performance reduces
4.) Here default partitioning technique would be Entire

Merge Stage:
1.) Here we have n inputs master link and update links andn-
1 reject links
2.) in this also we can perform 2 join operations: inner
join, left outer join
3.) the hash partitioning technique is used by default
4.) Memory used is very less, hence performance is high
5.) sorted data in master and update links are mandatory

Answer / jana520

all are used to join tables , but

lookup: when the reference data is very less we use lookup.
bcoz the data is stored in buffer. if the reference data is
very large then it wl take time to load and for lookup.

join: if the reference data is very large then we wl go for
join. bcoz it access the data directly from the disk. so the
processing time wl be less when compared to lookup. but here
in join we cant capture the rejected data. so we go for merge.

merge: if we want to capture rejected data(when the join key
is not matched) we use merge stage. for every detailed link
there is a reject link to capture rejected data.

Answer / maruthi

ALL THESE THREE(MERGE,JOIN,LOOKUP) ARE USED TO JOIN TABLES
BASED ON THE KEY COLUMNS. AND THE DIFFERENCES ARE:
1.)MAIN DIFFERENCE:ALL THESE THREE WILL DIFFER ON THE
POPULATION OF DATA ONCE AFTER KEY COLUMN MATCHES,AND THE
MEMORY USED TO STORE TABLES.
MERGE:-CAN HAVE ANY NUMBER OF INPUT LINKS,SINGLE O/P
LINK,AND NO OF REJECT LINKS AS MANY OF UPDATE LINKS,SO WE
CAN HAVE REJECT DATA IN ANOTHER TABLES,(JOINER DONT
SUPOERTS ANT REFERENCE OR REJECT LINKS)

Answer / rahul

all the three stages are differ with each other mainly
depends on three categories

1)input column requirements
a) sorting
b)de duplication
2)treatment of unmatched data
3)memory usage

1.. sorting in joins and merge in primary table and
secondary table is mandatory where in look up its optional.
de duplication in joins its allowed no warnings and no
job aborts.
in case of look up in primary table its accepted but in
secondary it raises warnings.
in merge primary table raises warnings in secondary
table its accepted.


about treatment of unmatched data and about memory discussed
above by some one..


thank you

Answer / kpk

all three stages are used to join database tables based on a
key column.

Lookupsate: input 1 reference any number (if oracle or DB2
only 1 reference link) one out put link and one reject link.
faster if the volume of data is less than the memory size.
if the siz is too huge then DS uses scrap files to store the
remaining datas and that hinders the performance.

Joinstage: can have any (but i think only 16 )tables can be
joined. does not use memory, look up is done on table level,
so would be better to use if the data volume is pretty
huge.dosent have any reject link. only one out put link.

Mergestage: can have any number of input link and update
link. need to have a key column. can have any number of
reject link. only one out put link.

Answer / kishore

ANother different is Lookup dont do sorting internally ,
where Merge and Join stage do sorting while data processing .

2. If there are dpluciate records at source , Merge stage
will gives warning but Join stage wont give ,

Answer / venki

lookup having one input link and n intermediate links one
reference link and one optional reject link
input data in sorted order
fore types of look are there
1.normal lookup
2.sparce lookup
these two more added in 8.1
3.range lookup
4.caseless sensitive
normal lookup
while doing normal lookup frist the reference data is
loaded in to memory this is used when the reference data in
high
sparce lookup
while doing the sparce lookup first for each input record
generate a sql quarry and made the operation in datadase
only one reference link the reference link should be
database or lookup file set only no intermediate links
this is used when the reference data is in low

Answer / pavan

We go for a join stage than a lookup when the referntial
data in look up is more ie.,>=500MB.we have outer joins in
join stage but not in merge stage.we have only inner join
in merge stage.

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