Remove duplicates

Hello

A conversation recently asked me the below question "if I have a table with a value of 10 billion records, which is partitioned and one of the partition has 1 billion documents, of which 10 million are duplicates. What is the fastest way to remove duplicates, based on a natural key that is Btree indexed"?

My first obvious answer (and the only one that I practically used tables up to a value of 1 million lines) was chunkwise delete using rowid or grade that is to say write a PL/SQL block and remove approximately 200,000 records in each iteration and commit after 200,000 records so that redo log and undo the memory space of the journal are not jumping. The interviewer asked a better/more quick. Frankly, I couldn't think of any other method.

PL/SQL has a bulk delete method? What's better than a regular or chunk-wise-commit-after-200K-deletes removal? Another way I could think of (I need to try this out however) is to create a SEPARATE table (partion xyz) AS select non partitioned table and then swap partition.

Someone of you have faced a similar situation and approach over time take? I will try the three method above, I could think of a few million lines (I can't put more than 5 million on my DB try otherwise, the DBA will raise a red flag. As a result, cannot test more than 5 million lines in the Dev env) but it cannot show the real difference compared to working with billions :-). Therefore ask any real project experience

Thank you

Sunny

Say the person with whom you had the conversation (interview?)?

Maybe the person plans to create the new table, insert select non-doublons of existing partition into the new table, and then use exchange partition...

Tags: Database

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