On 8/17/23 14:00, Frédéric Yhuel wrote:
On 8/17/23 09:32, Frédéric Yhuel wrote:
On 8/10/23 17:06, Juan José Santamaría Flecha wrote:
Recently I restored a database from a directory format backup and
having this feature would have been quite useful
Hi,
Thanks for resuming work on this patch. I forgot to mention this in my
original email, but the motivation was also to speed up the restore
process. Parallelizing the FK checks could make a huge difference in
certain cases. We should probably provide such a test case (with perf
numbers), and maybe this is it what Robert asked for.
I have attached two scripts which demonstrate the following problems:
Let me add the plans for more clarity:
1a. if the tables aren't analyzed nor vacuumed before the post-data
step, then they are index-only scanned, with a lot of heap fetches
(depending on their size, the planner sometimes chooses a seq scan
instead).
https://explain.dalibo.com/plan/7491ga22c5293683#raw
1b. if the tables have been analyzed but not vacuumed before the
post-data-step, then they are scanned sequentially. Usually better, but
still not so good without a parallel plan.
https://explain.dalibo.com/plan/e92c5161g880bdhf#raw
2. if the visibility maps have been created, then the tables are
index-only scanned without heap fetches, but this can still be slower
than a parallel seq scan.
https://explain.dalibo.com/plan/de22bdb4ggc3dffg#raw
And at last, with the patch applied :
https://explain.dalibo.com/plan/54612a09ffh2565a#raw
