Use this procedure to estimate the size of your journal receiver.
This procedure assumes the following:
- You are journaling after-images only.
- You are using a single journal receiver for an entire day's transactions.
- You are journaling database physical files only. It does not include estimates
for access path journaling, integrated file system objects, data areas, data
queues, or user-created entries.
- You are not using the MINENTDTA parameter to minimize entry-specific data
for the files.
- Most of the journal entries are record-level (changes to
records in a file) instead of object-level (like renaming or moving objects,
ALTER TABLE requests, creating and deleting objects, etc).
Follow the steps below to estimate the size of a journal receiver:
- Determine the average record length for all the files
that you plan to journal. If the record lengths vary significantly and the
information is available, use a weighted average based on the relative number
of transactions per file.
- If you are not minimizing the fixed-length portion
of the journal entry (not specifying RCVSIZOPT(*MINFIXLEN) on the CRTJRN command),
you can specify the data that is included in the fixed-length portion (FIXLENDTA)
of the journal entries. Find the sum of the bytes for the options you are
using. Select the options from the following list:
- *JOB = 26 bytes
- *USR = 10 bytes
- *PGM = 10 bytes
- *PGMLIB = 22 bytes
- *SYSSEQ = 8 bytes
- *RMTADR = 20 bytes
- *THD = 8 bytes
- *LUW = 27 bytes
- *XID = 140 bytes
- Estimate the number of transactions for a day.
- The system-created portion of a journal entry is approximately
50 bytes. (It varies by the type of journal entry.)
- Estimate the number bytes of auxiliary storage needed for one day's
transactions by using the following formula:
Total bytes needed = (a+b+50)*c
where:
- a = the average record length of files (step 1)
- b = sum of values selected for FIXLENDTA (step 2)
- c = number of transactions for a day (step 3)
For example:
- The average record length for journaled files is 115 bytes.
- *JOB, *USR, and *PGM options of FIXLENDTA are selected. Their sum is 46
bytes.
- The number of journaled transactions per day is 10 000.
- The total bytes needed to journal after-images for a day is:
(115+46+50) * 10 000 = 2 110 000