Persistent Staging Area
The Persistent Staging Area (PSA) is the inbound storage area in BW for data from the source systems. The requested data is saved, unchanged from the source system. Request data is stored in the transfer structure format in transparent, relational database tables of the BW system in which the request data is stored in the format of the DataSource. The data format remains unchanged, meaning that no summarization or transformations take place, as is the case with InfoCubes.
When you load flat files, the data does not remain completely unchanged as it may be modified by conversion routines (for example, the date format 31.12.1999 might be converted to 19991231 in order to ensure the uniformity of the data).
The possible coupling of the load process from the further processing in BW contributes to an improved load performance. If errors occur when data is processed further, the operative system is not affected.
The PSA delivers the backup status for the ODS layer (until the total staging process is confirmed). The duration of the data storage in the PSA is medium-term, since the data can still be used for reorganization. However, for updates to DataStore objects, data is stored only for the short term.
A transparent PSA table is created for every DataSource that is activated. The PSA tables each have the same structure as their respective DataSource. They are also flagged with key fields for the request ID, the data package number, and the data record number.
InfoPackages load the data from the source into the PSA. The data from the PSA is processed with data transfer processes.
With the context menu entry Manage for a DataSource in the Data Warehousing Workbench you can go to the PSA maintenance for data records of a request or delete request data from the PSA table of this DataSource. You can also go to the PSA maintenance from the monitor for requests of the load process.
Using partitioning, you can separate the dataset of a PSA table into several smaller, physically independent, and redundancy-free units. This separation can improve performance when updating data from the PSA. In the Implementation Guide with
SAP NetWeaver 
Business Intelligence Links to Other Source Systems Maintain Control Parameters for the Data Transfer 
you define the number of data records needed to create a new partition. Only data records from a complete request are stored in a partition. The specified value is therefore a threshold value.
The number of fields is limited to a maximum of 255 when using TRFCs to transfer data. The length of the data record is limited to 1962 bytes when you use TRFCs.