DB2 UDB for z/OS Version 8 Performance Topics - IBM Redbooks

5.1.1 Performance
MB as default. The FLA design consists of one log read task per recover job and one or more
log apply tasks employing the use of multitasking whenever possible. It takes advantage of list
prefetch and nearly eliminates duplicate synchronous read operations for the same page. It
achieves these efficiencies by sorting groups of log records together that pertain to the same
table space before applying those changes; it then applies those records in parallel using
several log apply tasks, up to 99.
When LOGAPSTG=0 is specified, DB2 restart will still use a minimum buffer size of 100 MB
for FLA during the forward log recovery phase. RESTORE SYSTEM and RECOVER will not
use FLA.
When LOGAPSTG> 0 is specified then:
► DB2 will use that value for the FLA buffer at restart time with a default of 100 MB.
► RESTORE SYSTEM will use FLA during the log apply phase. RESTORE, with APAR
PQ95164, will always try to allocate a FLA buffer of 500 MB. If it cannot get the storage, it
retries with 250 MB, 125 MB, and so on.
► Each concurrent recover utility will use a buffer of 10 MB out of the storage defined by
LOGAPSTG. If no more storage is available, the next concurrent recover utility will execute
without FLA. This means that the maximum value of 100 MB for LOGAPSTG allows for 10
concurrent recover utilities executing with FLA, the 11th recover will execute without FLA.
For a detailed description on Point-in-Time Recovery, and other disaster recovery functions,
see Disaster Recovery with DB2 UDB for z/OS, SG24-6370.
In this section we describe the System Level point-in-time recovery performance
measurement.
Performance measurement description
For this measurement we used:
► z/OS V1R5 with DFSMS, DFSMSdss, and DFSMShsm V1R5
► DB2 V8
► zSeries 2084 Model 316
► ESS 2105-800, FlashCopy V2
► Copy pool:
– Database copy pool either 67 (27% full) or 195 volumes (10% full)
– Log copy pool 13 volumes
► Copy pool backup:
– 211 volumes for the database copy pool
Up to 3 versions available to the 67-volume copy pool
One version only for the 195-volume copy pool
– 13 volumes for the log copy pool
1 version for the 13-volume log copy pool
Performance measurement results
In this section we present the System Level point-in-time recovery performance measurement
results.
FRBACKUP PREPARE measurements
See Figure 5-1 for the measurement results of FRBACKUP PREPARE. The results show a
non-linear behavior between elapsed time to prepare and the number of volumes in the pools.
Chapter 5. Availability and capacity enhancements 221