Storage Estimates for Checkpoint Data Sets

The following information can be used as a guideline in determining the size of this data set.

Table 1 contains the size and number of records written when a checkpoint is taken. The number of tracks or the amount of tape occupied by the checkpoint data set can be determined by applying the number of records and their sizes against either the track capacities of the direct access device or the recording density and type for the magnetic tape device.

Table 1. Determining the Size of a Checkpoint Data Set
Description of Record	Size (in bytes)	Number Required
Checkpoint header record (CHR)	400	1
DD name table (DDNT)	400	(((D+20)/21)+1)/2
Data set descriptor record (DSDR)	400	(A+1)/2
Problem program image record (PPIR)	4096	B
Supervisor record (SUR)	4096	C
Subsystem checkpoint record (SSCR)
subsystem data sets	4096	Number of SYSIN or SYSOUT plus number of DDs with SUBSYS=
SPIE	20/4096	E/20
VSAM	4096	1
*Records Code: A = the number of data sets defined in the job step B = (Storage allocated - freespace + (20 number of gaps in allocated storage))/4076. Example of calculation of B: Storage allocated = 9000 to 4FFFF and 1A000000 to 2FFFFFFF Freespace=

Address	Size	Number of Gaps
A200 to A3FF	200	1
32900 to 35FFF	3700	1
40000 to 47FFF	8000	1
50000 to 19FFFFFF	0	1 (not allocated; counts as a gap)
1F900000 to 210F8FFF	17F9000	1
28700000 to 29FFFFFF	1900000	1
=	3104900	6
Therefore: B = ((47000 + 16000000) - 3104900 + (X'14' * 6)) /X'FEC' B = 130C0 Note: All values in the above example are in hexadecimal. C = A variable number of records for system and protected data management control blocks. This will be approximately three records plus one record for every three DASD data sets and one record for every ten non-DASD data sets. D = Number of JCL-specified data sets dynamically unallocated at checkpoint. E = One for every 90 ESPIEs established before checkpoint.

Checkpoint/restart's dynamic storage requirement varies with the resources used by the caller. The largest impact on the dynamic storage requirement results from the amount of storage allocated to the job and the amount of storage fragmentation. Checkpoint/restart's dynamic storage is allocated out of subpools 229 and 230.