The Retrieve Deleted Records command allows the retrieval of deleted
records from a physical file. Some restrictions exist such as no
variable length records, null fields, or REUSEDLT(*YES). Deleted
records cannot be retrieved if RGZPFM occurs or CLRPFM.
A typical command would be:
RTVDLTRCD FROMFILE(xxx) TOFILELIB(yyy)
This would extract the deleted records in the FROMFILE and write them
to the same named file in the library specified for TOFILELIB.
When a record is deleted in a data base file, the data values still
exist, but the system places a special hex value in front of the
record specifying that it is deleted. The Operating System prevents
any access to a deleted record thru its normal interfaces.
When the file is saved, all the information from both active and
deleted records are saved. The RTVDLTRCD command saves the file you
specified to a save file and then searches for the deleted records
and writes them to the same file name in a different library.
When a file is cleared, the end of file indicator is set back to the
beginning of the file and the records cannot be retrieved with
RTVDLTRCD. When a file is reorganized, the data is copied to a
temporary file without the deleted records. Therefore, deleted
records cannot be retrieved after RGZPFM.
There are a few things to consider:
** RTVDLTRCD can only be used by the owner of the file, if the
owner is the group profile of the current user, or a user with
*ALLOBJ authority.
** A file of the same name as the file you are retrieving from
must not exist in the TOFILELIB. A new file will be
automatically created using the format of the FROMFILE.
** An option exists to allow a relative record number field to be
added to the new file. This will contain the relative record
number of where the record was found in the FROMFILE.
** Files with variable length fields or null fields are not
supported.
** No date information is kept by the system on when the record
was deleted.
** Files with Date (L), Time (T), or Timestamp (Z) type fields
are supported. Although the system keeps the data for these
fields in a different format that is seen in the data
management buffer, RTVDLTRCD simulates what the system does to
map the data into a record buffer before writing the record.
There is a restriction where these types of fields cannot
exist in the first 5 positions of the record. See the
following discussions.
If the records retrieved contain only blanks or zeros, see the next
two sections.
How RTVDLTRCD operates internally
---------------------------------
The file is checked to ensure it contains deleted records and if none
exist, an error message occurs.
The file definition is checked to determine if any field types (such
as variable length) exist and if so, RTVDLTRCD sends an error
message.
If Date, Time, or Timestamp fields exist, the actual record length of
the record when Saved is calculated (this will be less than the
external record length as seen by DSPFD).
A duplicate file definition is created in QTEMP and a single record
is initialized in this file. The record is then updated so the
characters *TAA* exist in positions 1 - 5.
The real file data is then copied (added to) to this duplicate
version. A save file is created in QTEMP and the QTEMP version of
the file is saved.
The save file data is then read by a program that scans for the first
record (the *TAA* record). Once it is found, the program knows where
to start in the save file data to check for records.
Each record is preceded by a single byte that determines whether it
is a 'live' or 'deleted' record. When a deleted record is found, it
is written to the file in the TOFILELIB parameter. Special handling
must occur if any Date, Time, or Timestamp fields exist as the data
must be reformatted to appear in the buffer as expected by data
management.
Determining if deleted records contain blanks or zeros
------------------------------------------------------
In some cases RTVDLTRCD may produce a new file that contains all
blanks and zeros for data. This may be due to an application program
which initializes the format of the record before deleting it.
You can determine if the deleted records actually contain blanks and
zeros by using the CHKDLTRCD command (part of the RTVDLTRCD tool)
with the exception of files defined with:
- Null values
- Variable length fields
- Reuse deleted records
Do the following:
** Use PRTDLTRCD for the file and member. This will print a
listing of where the deleted records are. Try to find a range
where several deleted records exist consecutively. For
example, if the listing shows a 'Start RR Nbr' of 1000 and
'Ending RR Nbr' of 1099, there are 100 consecutive deleted
records beginning at relative record number 1000. If you have
a reasonable range of consecutive deleted records, you should
have the information you need to make a determination if
blanks and zeros exist.
** Determine the relative record number of the first record prior
to a group of consecutive deleted records. In the example of
100 consecutive deleted records beginning at 1000, relative
record number 999 is the first active prior record.
** Determine a unique value in this active record. Knowing what
the first active data record looks like will help you
determine where the deleted records begin when displayed. A
good tool to use is DSPDB:
DSPDB FILE(xxx) FROMRCD(nnn)
Identify a unique value in the record such as few bytes from a
name field. You need to know the approximate position in the
record where the unique value exists and how long the record
is.
** Enter the following command using the FROMRCD as the relative
record number of the first active record prior to the
consecutive group of deleted records and the TORCD as the last
relative record number in the group.
CHKDLTRCD FILE(xxx) MBR(yyy) FROMRCD(nnn) TORCD(nnn)
This will create the TEMPFILE in QTEMP, by copying the range
of relative record numbers you specified. A save file
(TEMPSAVF) is then created in QTEMP, and the created data base
file is saved. The save file is then copied to the RCD528
file in QTEMP and the file will be displayed using DSPPFM.
Each record in a save file is 528 bytes long. The last 12 or
so bytes contain control information in each record. A data
record may be completely contained in the save file record or
it may span a record. There is a byte that precedes the data
for each record that determines if the record is valid or
deleted. In some cases, a record will span the 528 byte area.
** Instructions will appear about how to use the DSPPFM display
to determine the data in your deleted records. You need to
scan for the unique value in the first active record (the
beginning of the file has a good deal of Save/Restore
information that you want to bypass).
Use F10 to display the data in hexadecimal. Then determine
whether the following deleted records contain blanks or zeros.
Date and Time Fields
--------------------
If your file contains date and time fields, the length which exists
on disk and the buffer length as seen by a program differ. DSPPFM
will display the value as kept on disk which is compressed as
follows:
Type of field Disk length Buffer length
------------- ----------- -------------
L = Date 4 10
T = Time 3 8
Z = Timestamp 10 26
When the data appears for date/time values, you will not be able to
determine the actual value because of the compression technique.
Look for data in fields other than date and time fields.
Operating on a locked file
--------------------------
Because a SAVOBJ must occur to access the records, RTVDLTRCD will
fail if the file is open for update.
CPYF should be considered in this case to copy the file to a work
file and retain the deleted records. Use FROMRCD(1) and
COMPRESS(*NO) when copying.
Working with the deleted records
--------------------------------
In some situations, you may want to recover only some of the deleted
records that have been retrieved. You could do the following:
** Specify RELRCD(*YES) on the RTVDLTRCD command. This will
provide you with a simple unique key for each record
retrieved.
** Get a printed listing of the deleted records and include the
relative record number. You could use the TAA tool DSPDBF.
** Determine what deleted records you want to recover.
** If you only want a few, you could use CPYF with the INCREL
parameter and specify the field name for the relative record
number. For example, assume you retrieved the deleted records
from FILEA in LIB1 and wrote the records to LIB2. A new FILEA
is automatically created in LIB2 with just the deleted
records. It uses the same format plus a field for relative
record number. Assume you created FILEA2 in LIB2 as a
duplicate of FILEA in LIB2 and want to copy record number 26
(this was the record at relative record number 26 in FILEA in
LIB1).
CPYF FROMFILE(LIB2/FILEA)
TOFILE(LIB2/FILEA2)
MBROPT(*ADD)
INCREL((*IF TAAREL *EQ 26))
** If you want to use most of the deleted records, you could use
DFU to delete those that you did not want.
** When you have a net file of the records you want to recover,
you can use CPYF to copy back to the original file. Note that
the records will not be written back to the original record
numbers. If you need to reuse the exact same relative record
numbers, you could write a program to do so using the TAARR
field.
RTVDLTRCD Command parameters *CMD
----------------------------
FROMFILE The qualified file name of the file to retrieve the
deleted records from. The library value defaults to
*LIBL.
TOFILELIB The library where a duplicate file will be created
to hold the deleted records. The same file name
will be used. The file must not exist in the
TOFILELIB. The format of the original file is used
(Also see the RELRCD parameter). The new file will
be created in arrival sequence (no key fields).
FROMMBR The member of the FROMFILE to be used. The default
is *FIRST.
RELRCD A *YES/*NO value that defaults to *NO. *YES
specifies that you want a relative record number
field to be added to each record in the new file.
The field (TAARR) will contain the relative record
number of where the record was in the FROMFILE. The
relative record number field will be added at the
end of all other fields in the format and is defined
as packed with 13 digits and 0 decimals.
CHKDLTRCD Command parameters *CMD
----------------------------
FROMFILE The qualified file name of the file to check for
deleted records. The library qualifier defaults to
*LIBL. *CURLIB may also be used.
FROMRCD The 'from relative record' number to check. See the
tool documentation section on 'Determining if
deleted records contain blanks or zeros'.
TORCD The 'to relative record' number to check. See the
tool documentation section on 'Determining if
deleted records contain blanks or zeros'.
MBR The member name to be checked. The default is
*FIRST for the first member of the file. *LAST may
be specified to check the last member in the file.
ALWACTIVE Whether to allow active records in the range of
FROMRCD/TORCD.
*YES is the default to assume that you are beginning
the copy with the first active record prior to a
group of consecutive deleted records.
*NO may be specified if the range of records should
include only deleted records.
Restrictions
------------
** The RTVDLTRCD command can only be used by the owner of the
file or a user with *ALLOBJ authority.
** The deleted records must still exist in the file. This means
that you have not done a CLRPFM, RGZPFM etc.
** If the file is specified as REUSEDLT(*YES) you may have
already added a new record on top of a deleted record you
would like to recover.
** Only a physical data file can be specified. Source files or
logical files may not be used (The typical use of source files
is with SEU which uses a work space so that all records are
written back when SEU ends so that there are no deleted
records).
** Files with variable length fields or null fields are not
supported.
** Graphic type fields are not supported.
** A minimum record size of 5 bytes is supported.
** A maximum record size of 4000 bytes is supported.
** The maximum number of fields in the file cannot exceed 998.
Prerequisites
-------------
To help control the use of the command, it must be created by the
Security Officer or a member of his group. The command is created
with the public excluded.
The following TAA Tools must be on your system:
CHKOBJ3 Check object 3
CPYFRMSAVF Copy from save file
CVTDAT2 Convert date 2
EDTVAR Edit variable
DUPFILFMT Duplicate file format
HLRMVMSG HLL Remove message
PAUSE Pause
RSNLSTMSG Resend last message
RTVDBFA Retrieve data base file attributes
RTVFLDARR Retrieve field array
RTVPFSRC Retrieve PF source
SNDCOMPMSG Send completion message
SNDDIAGMSG Send diagnostic message
SNDESCMSG Send escape message
SNDSTSMSG Send status message
WRTSRC Write source
Implementation
--------------
None, the tool is ready to use.
Objects used by the tool
------------------------
Object Type Attribute Src member Src file
------ ---- --------- ---------- ----------
RTVDLTRCD *CMD TAADBFW QATTCMD
CHKDLTRCD *CMD TAADBFW4 QATTCMD
TAADBFWC *PGM CLP TAADBFWC QATTCL
TAADBFWC2 *PGM CLP TAADBFWC2 QATTCL
TAADBFWC3 *PGM CLP TAADBFWC3 QATTCL
TAADBFWC4 *PGM CLP TAADBFWC4 QATTCL
TAADBFWR *PGM RPG TAADBFWR QATTRPG
TAADBFWR2 *PGM RPG TAADBFWR2 QATTRPG
TAADBFWR3 *PGM RPG TAADBFWR3 QATTRPG
TAADBFWR5 *PGM RPG TAADBFWR5 QATTRPG
TAADBFWR9 *PGM RPG TAADBFWR9 QATTRPG
Structure
---------
RTVDLTRCD Cmd
TAADBFWC CL Pgm
TAADBFWR2 RPG pgm to check for var len fields etc
TAADBFWC2 CL Pgm Checks authority
TAADBFWR RPG Pgm Reads save file data
TAADBFWC2 CL Pgm Checks authority
TAADBFWR5 RPG Pgm Handles reformatting of Date/Time etc
TAADBFWR9 RPG Pgm Determines yyyymmdd for disk format
TAADBFWC3 CL Pgm Does CVTDAT2 from yyyymmdd
CHKDLTRCD Cmd
TAADBFWC4 CL Pgm
|
