OTBI and BI are giving Heap size error

Content

Hello,

We have a requirement to create a OTBI/BI report to get employee's information if employee is missing any of below field values.

Correspondence Language/Email Address/Assignment Name/Grade/Department Name/Action Reason/Manger/Cost center

Process name	Bus. unit	Division	Legal entity	Department	Field missing	Field use *	First name	Last name	Worker number
Performance	B1	D1	L1	Controlling	Assignment Name	RI	ABCDE	Fghijk	1234
Performance	B1	D1	L1	Controlling	Grade	RI	ABCDE	Fghijk	1234

 

if an employee is does not have his Assignment name and Grade, report should bring two records as below. We created a OTBI report by combining the same subject area 8 times using union all operator. it was working fine in DEV instance but once migrated to SIT, started giving Heap Size error.