{Blank Subject Dec 21, 1999}

Chris Hayes

{Blank Subject Dec 21, 1999}
While looking through some reports, I noticed that one of our production DB2
subsystems is checkpointing over 400 times an hour during certain times. I
checked our checkpoint frequency parameter and it is set at 50,000. IBM
recommends using 25,000 to 500,000 in their Installation Guide. Am I
correct in thinking that 400 times an hour is excessive? Should I be
concerned about raising the threshold? IBM's Installation Guide mentions
that start-up time may be excessive (over 30 minutes) if you specify a value
over 300,000 and you terminate DB2 without a quiesce. Is this a real
concern or should DB2 always be stopped with a quiesce?



Isaac Yassin

(in response to Chris Hayes)
Hi,

In my opinion you're way too low on checkpoint frequency. I try to keep it at
around once every 10-15 minutes.
It generates a hell lot of an I/O. The problem is that you can't adjust it
dynamically so sometimes it's too much and others much less. However since it
concerns amount of work done then you should move it up.
Mathematically speaking if you put in 500,000 it'll give you 40 times an hour on
you peak time which is still too often. I would go to 2,000,000 based on your
data.

please pay attention to the following in Admin Guide:

At least one checkpoint is taken each time DB2 switches to a new active log
data set. If the data sets are too small, checkpoints occur too
frequently. As a result, database writes are not efficient. Provide enough
active log space for 10 checkpoint intervals. For estimation
purposes, assume that a single checkpoint writes 24KB (or 6 control
intervals) of data to the log. A checkpoint interval is defined by the
number you specify for checkpoint frequency (see Section 2 of Installation
Guide). Make sure that the number you specify multiplied by 10 is
less than the number of changes per hour multiplied by the number of hours
per archive.

So you have to size your active log files accordingly as well.

Good luck

--
Isaac Yassin

DBMS & IT Consultant

Tel: +972 9 9505172
Cel: +972 54 452793
Fax: +972 9 9560803



"Hayes, Chris" wrote:
>
> While looking through some reports, I noticed that one of our production DB2
> subsystems is checkpointing over 400 times an hour during certain times. I
> checked our checkpoint frequency parameter and it is set at 50,000. IBM
> recommends using 25,000 to 500,000 in their Installation Guide. Am I
> correct in thinking that 400 times an hour is excessive? Should I be
> concerned about raising the threshold? IBM's Installation Guide mentions
> that start-up time may be excessive (over 30 minutes) if you specify a value
> over 300,000 and you terminate DB2 without a quiesce. Is this a real
> concern or should DB2 always be stopped with a quiesce?
>
>
>



DANIEL CYR

(in response to Isaac Yassin)

Yes taking a checkpoint 400 times an hour is REALLY excessive.
Think of it your checkpointing 6.4 times per minute.

Currently our checkpoint frequency is set at 200,000 and that's on
a very busy sysplex.

Good luck...


______________________________ Reply Separator _________________________________
Subject: Author: [login to unmask email] at INTERNET
Date: 12/21/1999 11:19 AM


While looking through some reports, I noticed that one of our production DB2
subsystems is checkpointing over 400 times an hour during certain times. I
checked our checkpoint frequency parameter and it is set at 50,000. IBM
recommends using 25,000 to 500,000 in their Installation Guide. Am I correct
in thinking that 400 times an hour is excessive? Should I be concerned about
raising the threshold? IBM's Installation Guide mentions that start-up time
may be excessive (over 30 minutes) if you specify a value over 300,000 and
you terminate DB2 without a quiesce. Is this a real concern or should DB2
always be stopped with a quiesce?


visit the