APPN checkpointing data sets
- SYS1.DSDB1
- SYS1.DSDB2
- SYS1.DSDBCTRL
- SYS1.TRSDB
SYS1.DSDB1 and SYS1.DSDB2 contain APPN directory information that is used to initialize the directory database when z/OS Communications Server is restarted.
Directory database information is stored alternately between SYS1.DSDB1 and SYS1.DSDB2. The directory database information is written to one of the data sets whenever a MODIFY CHKPT TYPE=ALL or TYPE=DIR, HALT, or HALT QUICK command is issued.
- Targeted by a search
- Have a dynamic entry type that is not registered
- Updated within a period of time specified by the DIRTIME start option
SYS1.DSDBCTRL contains the current status of SYS1.DSDB1 and SYS1.DSDB2. It is read by z/OS Communications Server during initialization to determine whether SYS1.DSDB1 or SYS1.DSDB2 will be used to load the APPN directory database.
SYS1.TRSDB is required for checkpointing the network topology database. The information in this data set is used to initialize the network topology database whenever z/OS V2R3 Communications Server is restarted. The network topology database is written to this file whenever a MODIFY CHKPT TYPE=TOPO or TYPE=ALL, HALT, or HALT QUICK command is issued.
- Specify the DD name for SYS1.DSDB1 as DSDB1, for SYS1.DSDB2 as DSDB2, for SYS1.DSDBCTRL as DSDBCTRL, and SYS1.TRSDB as TRSDB.
- Specify these DCB subparameters for SYS1.DSDB1, SYS1.DSDB2, and
SYS1.TRSDB:
RECFM=FB,LRECL=1000,BLKSIZE=any multiple of 1000,DSORG=PS
- Specify these DCB subparameters for SYS1.DSDBCTRL:
RECFM=FB,LRECL=20,BLKSIZE=20,DSORG=PS
- The DSDBCTRL is a fixed, 20-byte file; it requires a 20-byte block.
Regarding DSDB1 and DSDB2: Every thousand resources to be checkpointed occupies 35 logical records, or six 6KB blocks of space; the only resources to be checkpointed are the cache DLU entries found during the search.
- z/OS Communications Server fails the initial load of the network topology database if the checkpointed data set of another node is used, or the SSCPNAME operand is changed between the two IPLs. Should the initial load fail, z/OS Communications Server can acquire the information dynamically using TDUs.