On 3/22/16 9:36 AM, Amit Kapila wrote:
 > > Note, that we are doing it only when a transaction has less than
equal to
 > > 64 sub transactions.
 > So?

They should fall on one page, unless they are heavily interleaved as
pointed by you.  I think either subtransactions are present or not, this
patch won't help for bigger transactions.

FWIW, the use case that comes to mind here is the "upsert" example in the docs. AFAIK that's going to create a subtransaction every time it's called, regardless if whether it performs actual DML. I've used that in places that would probably have moderately high concurrency, and I suspect I'm not alone in that.

That said, it wouldn't surprise me if plpgsql overhead swamps an effect this patch has, so perhaps it's a moot point.
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com

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