Followup on the 4k DML bug

Another piece of good news — Oracle has opened a bug for yet another anomaly I reported earlier in my blog: row-by-row processing of bulk DML when the block size on the target table is less than the default 8k. So it’s now officially bug 20039770 – “DML SLOW WITH 4K BLOCK SIZE VS 8K BLOCK SIZE”. Their bug description seems a bit off (because 2K shows the same behavior as 4K, and 16/32K as 8K, so it’s not really a case of “4K VS 8K”), but I’m sure they update it accordingly in the course of the investigation by the development team. Unlike the log parallelism bug, this one is not yet open to public (maybe because they don’t have anything to put into the bug note yet, not even a workaround), I’ll post an update when that changes.

If you ever work with small block sizes then I highly recommend you familiarize yourself with this bug, because its impact on DML performance is quite big (I observed x3-x7 effect, but it could be even larger in a different setup). It makes rewrites of row-by-row logic via bulk DML pretty much useless, so if I had known about it earlier, it would have saved me a couple of weeks!

I will post another blog when Oracle concludes their investigation.

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