Question

I have an application that records activity in a table (Oracle 10g). The logging records should be kept for at least 30 days. I expect about 20 million rows to be added to this table every month.

The DBA suggested that the table be split in partitions containing one week of data. The weekly maintenance script would then delete the oldest partition (leaving only 4 weeks of data in the table).

What would be the best way of partitioning this logging table?

Answer 1

Partitioning a table isn’t hard – it appears that you will be removing the data on a weekly basis, so the partition clauses will look like

PARTITION "P2009_45"  VALUES LESS THAN 
(TO_DATE(' 2009-11-02 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN')),
 PARTITION "P2009_46"  VALUES LESS THAN 
(TO_DATE(' 2009-11-09 00:00:00', 'SYYYY-MM-DD HH24:MI:SS', 'NLS_CALENDAR=GREGORIAN')),
... etc

where your partitioning column is your date column of interest in the table.

Additional comments:

• If you can upgrade to 11g you can
  take advantage of interval
  partitioning, which is similar to
  this range partitioning, but Oracle
  will manage creating new partitions
  for you.
• If you’re going to routinely drop off
  partitions, I would advise making all
  indexes on the table
  locally-partitioned to avoid the
  rebuilds that would be necessary with
  global partitions after partition
  operations.
• If you have a good idea of the number
  of log entries per month, and it
  stays relatively constant, you might
  consider using a sequence (as a primary key) that is
  capped at this number and then
  recycles back to 0. Then your
  logging statements must become “MERGE
  INTO… ” statements that either
  create a new row or overwrite the row
  if it exists. This only guarantees
  that you’ll retain the number of rows
  allowed by the sequence max value and
  NOT a certain time interval, but this
  might be an alternative to
  partitioning (which as DvE points
  out, is an extra-expense option)