John wrote:
I can't find this in the manuals. I'm not interested in size of
primary or secondary logs, what is a good rule of thumb for how many
logs to cut in an hour in a busy OLTP and DW environment. I heard
every 15 minutes was a good starting point. Thx, Flick
The correct interval is:
It depends!
Many factors go into determining this value. Every installation will
have a different result; dependent on local factors. A couple of
examples follow. Note that I am exagerating sizes and effects.
Archive directly to tape, manual tape handling.
1. Log files are 20mb, system has active updating.
Result: Tapes have almost no data on them and an operator
is required full time to mount tapes for DB2.
2. Log files are 4g, system has active updating.
Result: Each log occupies multiple volumes of tape. When
an archive occurs, four drives are requested
(dual archiving, two drives per archive) and the
archive waits until the drives are available.
Alternatively, two drives are used (single copy)
and operations misplaces one of the volumes of
an archive, making it unusable.
3. Log files sized to fill a reel of tape, archives occur
3x/day.
Result: Company goes out of business after a water main
break occurs at 3:30pm and causes the loss of
logs from the tail end of batch processing and
almost an entire day's online processing. (This
assumes that the datacenter will be unusable
for two weeks to repair water damage.)
There's no "correct" interval for archiving. The mimimum interval should
be a length of time long enough that an archive will complete before the
next is requested. The longest is controlled by business factors and
archive objectives. I've seen some clients do a cost/benefit analysis to
determine an appropriate archive interval.
Archiving demands that the archive area have enough storage available to
accept what DB2 will be giving it. It also assumes that when DB2 needs
to archive that the archiver will immediately be able to process the
request.
Phil Sherman
