Re: Indirect indexes

On 10/18/2016 11:28 AM, Alvaro Herrera wrote:

> Vacuuming presents an additional challenge: in order to remove index
> items from an indirect index, it's critical to scan the PK index first
> and collect the PK values that are being removed. Then scan the
> indirect index and remove any items that match the PK items removed.
> This is a bit problematic because of the additional memory needed to
> store the array of PK values. I haven't implemented this yet.

As a whole I think the idea is interesting but the above scares me. Are
we trading initial performance gains for performance degradation through
maintenance? Since autovacuum is an indeterminate launch we could have a
situation where even a medium level updated laden table becomes a source
of contentions for IO and memory resources. I don't know that we would
see issues on modern bare metal but considering our implementation space
is places like RDS and GCE now, this is a serious consideration.

Sincerely,

JD

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