Changing the length of a key field in a table

Question

Hi,
I want to increase the length of the field from 2 to 4 in a standard SAP table and deliver it to the customers. This field is a key field in table. This field from this table is also used in view and view clusters.
What is the implication of changing the length to the customers. The customers would have already data in this field and they should not loose any data. Will the existing data for customers remain at length 2 or do they have to do some conversion?
Regards,
Srini.
Edited by: Srinivasa Raghavachar on Feb 7, 2008 12:45 PM

Answer 1

hi,
The database table can be adjusted to the changed definition in the ABAP Dictionary in three different
ways:
By deleting the database table and creating it again. The table on the database is deleted, the inactive
table is activated in the ABAP Dictionary, and the table is created again on the database. Data
existing in the table is lost.
By changing the database catalog (ALTER TABLE). The definition of the table on the database is
simply changed. Existing data is retained. However, indexes on the table might have to be built again.
By converting the table. This is the most time-consuming way to adjust a structure.
If the table does not contain any data, it is deleted in the database and created again with its new
structure. If data exists in the table, there is an attempt to adjust the structure with ALTER TABLE. If the
database system used is not able to do so, the structure is adjusted by converting the table.
Field 1     Field 2,    Field 3
NUMC,6  CHAR 8    CHAR, 60
Field 1    Field 2       Field 3
NUMC,6 CHAR, 8     CHAR,30
The following example shows the steps necessary during conversion.
Starting situation: Table TAB was changed in the ABAP Dictionary. The length of field 3 was reduced
from 60 to 30 places.
The ABAP Dictionary therefore has an active (field 3 has a length of 60 places) and an inactive (field 3
still has 30 places) version of the table.
The active version of the table was created in the database, which means that field 3 currently has 60
places in the database. A secondary index with the ID A11, which was also created in the database, is
defined for the table in the ABAP Dictionary.
The table already contains data.
Step 1: The table is locked against further structure changes. If the conversion terminates due to an
error, the table remains locked. This lock mechanism prevents further structure changes from being
made before the conversion has been completed correctly. Data could be lost in such a case.
Step 2: The table in the database is renamed. All the indexes on the table are deleted. The name of the
new (temporary) table is defined by the prefix QCM and the table name. The name of the temporary
Step 3: The inactive version of the table is activated in the ABAP Dictionary. The table is created on the
database with its new structure and with the primary index. The structure of the database table is the
same as the structure in the ABAP Dictinary after this step. The database table, however, does not
contain any data.
The system also tries to set a database lock for the table being converted. If the lock is set, application
programs cannot write to the table during the conversion.
The conversion is continued, however, even if the database lock cannot be set. In such a case
application programs can write to the table. Since in such a case not all of the data might have been
loaded back into the table, the table data might be inconsistent.
You should therefore always make sure that no applications access the table being converted
during the conversion process.
Step 4: The data is loaded back from the temporary table (QCM table) to the new table (with MOVECORRESPONDING).
The data exists in the database table and in the temporary table after this step.
When you reduce the size of fields, for example, the extra places are truncated when you reload the
data.
Since the data exists in both the original table and temporary table during the conversion, the storage
requirements increase during the process. You should therefore verify that sufficient space is available in
the corresponding tablespace before converting large tables.
There is a database commit after 16 MB when you copy the data from the QCM table to the original
table. A conversion process therefore needs 16 MB resources in the rollback segment. The existing
database lock is released with the Commit and then requested again before the next data area to be
converted is edited.
When you reduce the size of keys, only one record can be reloaded if there are several records whose
key cannot be distinguished. It is not possible to say which record this will be. In such a case you should
clean up the data of the table before converting.
Step 5: The secondary indexes defined in the ABAP Dictionary for the table are created again.
Step 6: The temporary table (QCM table) is deleted.
Step 7: The lock set at the beginning of the conversion is deleted.
If the conversion terminates, the table remains locked and a restart log is written.
Caution: The data of a table is not consistent during conversion. Programs therefore should not access
the table during conversion. Otherwise a program could for example use incorrect data when reading the
table since not all the records were copied back from the temporary table. Conversions therefore
should not run during production! You must at least deactivate all the applications that use tables to
be converted.
You must clean up terminated conversions. Programs that access the table might otherwise run
incorrectly. In this case you must find out why the conversion terminated (for example overflow of the
corresponding tablespace) and correct it. Then continue the terminated conversion.
Since the data exists in both the original table and temporary table during conversion, the storage
requirements increase during conversion. If the tablespace overflows when you reload the data from the
temporary table, the conversion will terminate. In this case you must extend the tablespace and start the
conversion in the database utility again.
If you shorten the key of a table (for example when you remove or shorten the field length of key fields),
you cannot distinguish between the new keys of existing records of the table. When you reload the data
from the temporary table, only one of these records can be loaded back into the table. It is not possible
to say which record this will be. If you want to copy certain records, you have to clean up the table
before the conversion.
During a conversion, the data is copied back to the database table from the temporary table with the
ABAP statement MOVE-CORRESPONDING. Therefore only those type changes that can be executed
with MOVE-CORRESPONDING are allowed. All other type changes cause the conversion to be
terminated when the data is loaded back into the original table. In this case you have to recreate the old
state prior to conversion. Using database tools, you have to delete the table, rename the QCM table to
its old name, reconstruct the runtime object (in the database utility), set the table structure in the
Dictionary back to its old state and then activate the table.
If a conversion terminates, the lock entry for the table set in the first step is retained. The table can no
longer be edited with the maintenance tools of the ABAP Dictionary (Transaction SE11).
A terminated conversion can be analyzed with the database utility (Transaction SE14) and then
resumed. The database utility provides an analysis tool with which you can find the cause of the error
and the current state of all the tables involved in the conversion.
You can usually find the precise reason for termination in the object log. If the object log does not
provide any information about the cause of the error, you have to analyze the syslog or the short dumps.
If there is a terminated conversion, two options are displayed as pushbuttons in the database utility:
After correcting the error, you can resume the conversion where it terminated with the Continue
adjustment option.
There is also the Unlock table option. This option only deletes the existing lock entry for the table .
You should never choose Unlock table for a terminated conversion if the data only exists in the
temporary table, i.e. if the conversion terminated in steps 3 or 4. table for table TAB is therefore QCMTAB.
Hope this is helpful,Do reward.