When a UAP uses a DAM file, the UAP accesses the file with the following procedure:

1. Open the file.
2. Perform one of the following processes:
   Data input (reference), data input and updating, and data output.
   
3. Close the file.

The function to open a DAM file must be called from each UAP that will use the DAM file. Even if more than one UAP belongs to one global transaction, each of the UAPs must call the function to open the DAM file.

• Recoverable DAM files
  Logical files can be opened both inside and outside the transaction. In the following cases, however, only block locking can be specified for logical files:
  
  • The logical file must be opened before the transaction starts.
  • Resource locking is specified for each global transaction.

DAM file blocks can be received without the specification of locking if the purpose of input is reference. If blocks are received without the specification of locking, the input blocks may not be up-to-date because other UAPs may update the blocks during the input processing.

Processes outside the transaction range (before the transaction starts or after the acquisition of the synchronization point) can only receive blocks by accessing them for a reference purpose. Blocks cannot be locked.

When DAM files are accessed, they are locked and unlocked for each transaction branch or for each global transaction. For details on locking of DAM files, see 4.1.7 Locking DAM files.

You cannot use DAM input or output functions (dc_dam_get, dc_dam_put, dc_dam_read, dc_dam_rewrite, dc_dam_write, CBLDCDMB('GET'), CBLDCDMB('PUT'), CBLDCDMB('READ'), CBLDCDMB('REWT'), and CBLDCDMB('WRIT')) to input or output DAM file data exceeding 2 gigabytes at one time. If you attempt to use one of these functions to input or output DAM file data exceeding 2 gigabytes, the function will return with a DCDAMER_BUFFER or 01604 error.