Re: Most efficient way to insert without duplicates

[François Beausoleil <francois@xxxxxxxxxxx>]

Le 2013-04-17 à 14:15, Jeff Janes a écrit :

On Wed, Apr 17, 2013 at 4:26 AM, François Beausoleil <francois@xxxxxxxxxxx> wrote:

 Insert on public.persona_followers  (cost=139261.12..20483497.65 rows=6256498 width=16) (actual time=4729255.535..4729255.535 rows=0 loops=1)
   Buffers: shared hit=33135295 read=4776921
   ->  Subquery Scan on t1  (cost=139261.12..20483497.65 rows=6256498 width=16) (actual time=562265.156..578844.999 rows=6819520 loops=1)

It looks like 12% of the time is being spent figuring out what rows to insert, and 88% actually doing the insertions.

So I think that index maintenance is killing you.  You could try adding a sort to your select so that rows are inserted in index order, or inserting in batches in which the batches are partitioned by service_id (which is almost the same thing as sorting, since service_id is the lead column)

In that case, partitioning the original table by service_id % N would help, since the index would be much smaller, right?

N would have to be reasonable - 10, 100, 256, or something similar.

Thanks,

François

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