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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.It covers how you can seed column usage to identify where there's a benefit in using extended statistics.Note that some column usage information is always captured to help identify columns that can benefit from histograms.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.This is how to prepare the LOAD table before the exchange: Q2 will have fresh statistics and a synopsis as soon as the exchange completes. Statistics on Q2 will be gathered again after the exchange (when statistics are gathered on SALES) unless you have created appropriate histograms and extended statistics on LOAD before the exchange.The list_script in Git Hub displays extended statistics and histograms for a particular table if you want to take a look at what you have.

To make this step as efficient as possible SALES must use incremental statistics maintenance.Most of you will be familiar with partition exchange load, but I’ll summarize it briefly to introduce you to the terminology I’ll be using here. Firstly, the LOAD table is filled with new data and then exchanged with a partition in the “live” application table (SALES).SALES has partitions for quarter 1 and quarter 2 (Q1 and Q2) and LOAD is exchanged with the empty Q2 partition.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.The effect of the exchange is to incorporate all of the data in LOAD into SALES by swapping the “identity” of LOAD with Q2.The exchange is a logical operation: a change is made in the Oracle data dictionary and no data is moved.This post covers how you can manage optimizer statistics efficiently when you use partition exchange load (PEL).This technique is used when large volumes of data must be loaded and maximum performance is paramount.For example: Statistics will be gathered on Q2 and the synopsis will be created so that the global-level statistics for SALES will be updated.Once the exchange has taken place, Q2 will need fresh statistics and a synopsis and it might also need extended statistics and histograms (if SALES has them).

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