Data Block Cleanup??

   I'm just curious more than anything, but I've noticed that if a database block belonging to a table segment is affected by an insert, delete, or update, then the next time a query accesses the block, something is done to it which causes it to be put on the DBWR dirty list.

   I first ran across this when I was loading up a table to do some volume testing (about 3 million rows). After loading the table, the first full table scan on it took forever. Subsequent table scans just flew. A quick check determined that every block read was being written back to the database on the first table scan.

   My pet theory is that Oracle is choosing this time to remove the old transaction entry (used by the previous update to the block and not removed on commit because of the obvious performance impact this would have).

   Can anyone enlighten me to whether I'm even close on this? Note that this does NOT seem to occur with index blocks.

• Doug Harris Database Administrator System Development Division Statistics Canada --