I'm looking for Lock and Timing considerations for ALTER of a multi-terabye table. We're considering using ALTER since we are not changing the PI or SI's and we don't need to rebuild our AJI's.
DNoeth has done a great job of explaining the difference between ALTER TABLE and INSERT/SELECT approach here: http://developer.teradata.com/blog/dnoeth/2013/08/why-dont-you-use-alter-table-to-alter-a-table
Is there any way to determine or estimate when the Tables Locks on DBC will occur?
How can I determine the system impact when the DBC locks do occur?
Do you have any thoughts on this?
In other words, you don't expect the ALTER TABLE to affect other DDL operations, e.g. CREATE VOLATILE TABLE unless that other DDL operation is directly referencing my large table. Makes sense.
What about the timing? Is there any way to estimate the duration of the LOCKs?
- Can I assume that the ALTER will only affect the table header.
- This table has several compressed columns with many values. Will this affect my run time?
The referenced article, http://www.teradatamagazine.com/table_dressing.aspx, indicates that in order to estimate time, we need to understand if the table header has enough room for the presense bits for our new NULL columns.
- If there is room for the NULL column presense bits, the ALTER could run quite fast.
- If no room, the ALTER will need to rewrite each block.
Maybe we can test this with a smaller copy of the table.
Hi, I am new to TD. I have a query about locks. If user palced a lock on database to execute a batch of transactions and DBA by mistake releases the lock with override on that specific database. Will it roll back that batch of transactions or what will happen exactly and may it harm the business logic or can leave some inconsistencies etc. if there is some effect because of this which log table have its record? Thank You