Re: Concurrent HOT Update interference

Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
> So what we have is that multiple UPDATEs repeatedly accessing the same
> block will prevent each other from successful cleanup, since while one
> session is performing the update, the second session is pinning the
> block with an indexscan.

> This effect has been noted for some time during pgbench runs, where
> running with more sessions than scale factors causes contention. We've
> never done anything about it because that's been seen as a poorly
> executed test, whereas it does actually match the real situation we
> experience at "hot spots" in the table.

Uh, no. pgbench's problem at high scale factors is that multiple
sessions want to update *the same row*, not just different rows on the
same page. That contention is unavoidable.

You may in fact have a good point, but you can't prove it by reference
to pgbench.

regards, tom lane

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