IBM 5695-DF1, 5655-DB2 manual Suspend Times, Synchronous I/O

BP4	TOTAL
---------------------	--------
BPOOL HIT RATIO (%)	50
GETPAGES	300350	F
BUFFER UPDATES	0
SYNCHRONOUS WRITE	0
SYNCHRONOUS READ	754
SEQ. PREFETCH REQS	702
LIST PREFETCH REQS	0
DYN. PREFETCH REQS	3944
PAGES READ ASYNCHR.	148634

Figure 63. DB2 PM Accounting, BP4 Section

12.1.3 Suspend Times

The class 3 section of the accounting report shows suspend (wait) times. This is shown in Figure 64 on page 145. These values are only shown if the accounting trace is started with class 3.

In this example, the wait times reported correspond to I/O. The application waited

56.77seconds for synchronous reads (A) and 29 minutes and 59.16 seconds for prefetch reads (B). This time is not directly attributable to the elapsed time, because the I/O was performed in parallel. On Figure 57 on page 142 we have the timing for parallelism. Only 3 minutes and 48.3 seconds (F in Figure 57) were in the main task (TCB). The remainder, 27 minutes and 7.7 seconds (G in Figure 57) were performed in the five parallel tasks.

CLASS 3 SUSP.	ELAPSED TIME	EVENTS
--------------	------------	-------
LOCK/LATCH	0.060799	2760
SYNCHRON. I/O	56.770913	19559	A
OTHER READ I/O	29:59.155952	143669	B
OTHER WRTE I/O	0.000000	0	C
SER.TASK SWTCH	0.002627	2
ARC.LOG(QUIES)	0.000000	0
ARC.LOG READ	0.000000	0
DRAIN LOCK	0.000000	0
CLAIM RELEASE	0.000000	0
PAGE LATCH	0.000000	0
STORED PROC.	0.000000	0
NOTIFY MSGS	0.000000	0
GLOBAL CONT.	0.000000	0
TOTAL CLASS 3	30:55.990291	165990

Figure 64. DB2 PM Accounting Class 3 Times

12.1.3.1 Synchronous I/O

Line A in Figure 64 on page 145 shows 19559 synchronous reads. This value is also reported as the total synchronous reads made by this query, F in Figure 66 on page 147. The elapsed time for these reads is 56.770913 seconds. This gives an average of 2.9 milliseconds for each read. This is a good response time for a direct access to a page. This response time is also shown in the DB2 PM highlights section, D in Figure 65 on page 146.

Case Study 145