General Driver Limits

This section lists various limitations of the UD6/CMtool driver, and where possible, and example of the impact of the limitation.

Commit and Rollback are not supported

If a Uniface session unexpectedly terminates DURING a commit or rollback operation, the XML file can effectively be destroyed. Often by careful examination, it can be recovered in a text editor. Fortunately the only reason that Uniface should ever crash DURING a commit or rollback is due to GPF's caused by the driver, which should not happen in regular operation.

Since Uniface is not a multi-threaded application, it only performs a single task at a time, the driver has complete control over execution during these operations. This significantly reduces the risk of a crash occurring and any resultant data loss. If you are particularly concerned about the risk of crashes March Hare advise that you use the UD6/CMtool Driver with Polyserver.

The other reason Uniface may terminate unexpectedly during a commit or rollback operation is user interruption with END TASK or by removing power from the PC or attached network devices.

Filenames and Table names are case-insensitive

Internally the driver does not distinguish between filenames and table names that are only different in their ‘case’ (either upper or lower case). Users should therefore avoid using files or tables that are identically named except for the case.

Limitations of Join

The joins file specifies how the UD6 driver should store several Uniface tables in a single file. This behavior has these limitations:

• No field in a Primary key (or Compound primary key) may contain spaces.
  
  
• Overflow cannot contain RAW characters (overflows in the Idf usually use packing code U that will translate all binary data into 7 bit ASCII.
  
  
• All the files for a particular JOIN are included in a single directory, that excludes all other files, especially temporary files, but also other XML files as well.
  
  
• Filenames (and field name entries in the join config file) are restricted to being in the field order, i.e.: if the fields are uvlab,uform then the filename is uvlab-uform.xml and the key must be in the same order.
  
  
• Partial keys are only supported if they are in sequence, eg:
  table zzz, has the fields a,b,c,d,e,f,g,h,j
  primary key is c,d
  index 2 is c
  index 3 is d
  
  The index #2 will be supported but index #3 will not.
  
  
• Filenames (see above) cannot contain illegal characters (e.g.: * or +).
  
  
• Maximum number of fields used to join is 4.
  
  
• The field name TRIGGER, is a reserved word (can be disabled with triggertag disable).

Other Limitations

The UD6 driver has several constants built in for predefined limits. This list is not intended to be definitive, but to give an approximate idea of the limits imposed:

• Maximum filename length 1024 Bytes.
  
  
• Maximum size of a line in an INUSE file 1024 Bytes.
  
  
• Maximum size of a USYS$UD6_ASN_SETTING is determined by Uniface not UD6.
  
  
• Maximum size of a directory listing string 1512 Bytes.
  
  
• Maximum size of combined primary key fields in overflow table 1024 Bytes.
  
  
• Maximum length of a fieldname 100 Bytes.

Further Information