Partitioning

There are times when you as a DBA wished you were involved before someone designed a data model. After release to production correcting mistakes is usually complicated and with risks. Update 2016-04-20: Fixed errors in code. There is an exception to this. Online table redefinition lets you change the structure of a table while everything is up and running. I have used it lately to partition large tables. During the process I also added compression, and moved some of the partitions to another tablespace that I have set read-only, in order to reduce backup time as well. LOBs in one table were moved to SecureFiles with deduplication. ...

In a earlier post about legacy databases I mentioned that dirty data are more likely to enter the database on an earlier stage. One day while I was looking at the selectivity for a few columns I found the values a bit strange. After some digging I noticed that for most of the time the data was OK, even though a proper foreign key constraint was missing for the columns. But at some time many years ago somebody had inserted something completely different , which had clearly affected the selectivity (the columns are indexed). ...