Re: MVCC overheads

Pete Stevenson wrote:

> Maybe I could figure out the lines of code that add versions into a
> table and then those that collect old versions (they do get collected,
> right?). Anyway, thought being I could profile while running TPC-C or
> similar. I was hoping that someone might be able to jump on this with
> a response that they already did something similar.

Old tuple versions are "collected" (removed) by either vacuum (see
vacuumlazy.c) and heap_page_prune. The latter is one thing that could
perhaps somehow be offloaded, as it's quite independent from the other
stuff. You can prune removable tuples at no additional cost from an
unlocked dirty page, which is a useful optimization because then
client-connected backends don't need to prune them later.

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Álvaro Herrera http://www.2ndQuadrant.com/
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