Program structure and data flow

IMS DEDB Fast Recovery processes eight internal program functions.

OLDS processing

Depending on the specified runtime options, IMS DEDB Fast Recovery selects the way to determine the last-used and previously used OLDS. It verifies the validity of the available OLDS, checking the time stamps of the log records. It creates the checkpoint ID table and the OLDS entry table.

Control block initialization I

IMS DEDB Fast Recovery checks the IMS MODSTAT, MODSTAT2, or OLCSTAT data set to determine the identifier (x) of the ACBLIBx data set that was in use at the time of IMS failure.

Checkpoint determination

IMS DEDB Fast Recovery determines the IMS checkpoint, from which the recovery processing will be started.

First log processing

IMS DEDB Fast Recovery loads or creates and initializes the IMS basic control blocks DDIR and DMAC after the FP checkpoint. Then IMS DEDB Fast Recovery analyzes log records after the selected checkpoint, reconstructs the database control blocks and DEDB buffers to the state that they were at the time of IMS failure, and determines the data CIs that need recovery.

Sync point determination for the transaction in process

IMS DEDB Fast Recovery writes a sync point abort log record for the transactions that did not reach a sync point, into the log data set, to abort the transaction. For in-doubt transactions, IMS DEDB Fast Recovery writes a sync point commit or abort log record into the log data set according to the specified control statements to determine whether the transaction is to be committed or aborted. Finally, IMS DEDB Fast Recovery closes the log data set.

Connection to block-level data-sharing VSO areas

If the IMS was using block-level data-sharing VSO areas when it failed, IMS DEDB Fast Recovery connects to the CF structures related to those areas.

Second log processing

IMS DEDB Fast Recovery starts the second reading with the log block that has the oldest updated data CI image to be recovered, and reconstructs the updated data CI images in the data space.

DEDB recovery and the recovery status list creation

IMS DEDB Fast Recovery recovers DEDB by using the data CI update images reconstructed in the data space, and creates the recovery status lists.

The following figure shows the control flow and data flow for these functions.