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In the example above, the global-level statistics for SALES must be refreshed to reflect the data incorporated into the table when LOAD is exchanged with Q2.To make this step as efficient as possible SALES must use incremental statistics maintenance.The data in LOAD is published to SALES “at the flick of a switch”.Typically, the exchange step looks like this: Operationally, this approach is more complex than inserting data directly into SALES but it offers some advantages.There is nevertheless a scenario where you might want to gather statistics on LOAD prior to the exchange.For example, if it’s likely that Q2 will be queried before statistics have been gathered on SALES then you might want to be sure that statistics are available on Q2 as soon as the exchange completes.I expect you'll have guessed from the title of this post that I’m going to assume that from now on!
SALES has partitions for quarter 1 and quarter 2 (Q1 and Q2) and LOAD is exchanged with the empty Q2 partition.
The moment after LOAD has been exchanged with Q2 there will be no synopsis on Q2; it won’t have been created yet.
Incremental statistics requires synopses to update the global-level statistics for SALES efficiently so a synopsis for Q2 will be created automatically when statistics on SALES are gathered.
For example, new data can be inserted into LOAD before any indexes have been created on this table.
If the volume of data is large, creating indexes at the end of the load is very efficient and avoids the need to bear the higher cost of index maintenance during the load.This happens even if you don't choose to seed column usage.Oracle Database 12c includes an enhancement that allows you to create a synopsis on LOAD prior to the exchange.It’s common to see it used in decision support systems and large operational data stores.