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Temporary table creation during insert is way higher than source table size?

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Hi Experts,

I saw the following behavior while trying to debug an out-of-memory issue, and hence wanted some inputs form experts.

1. Create a table as " create table ISSUEDEBUG like "SCHEMAXYZ"."COBK" "

 

2. insert into "EPANTRA"."ISSUEDEBUG" (select * from "LND_F08CLNT400_R"."COBK" )

Size of table COBK : 17GB

COBK_Size.png

3.Size of table ISSUEDEBUG during the insert operation>> 44GB+

ISSUEDEBUG_Size2.png

 

So, it seems some temporary table is getting generated during insert operation and its size is considerably larger than source table size.

4. Select count(*) query returns 0 count

count.png

Questions:

1. The size of temporary table goes way higher than source table size (even much higher than source system table size too).Why?

(Is delta memory/uncompression the reason or there is something more to it, as the size on source system is also 20GB)!!

 

3. This issue becomes critical for implementation if a Data Services job is trying to do this activity(moving data from a base to higher schema) with some transformation?

 

Regards,

Rahul


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