Re: query plan not optimal

>
> QUERY PLAN
>
> ----------------------------------------------------------------------------------------------------------------------------------
> Nested Loop (cost=0.56..4001768.10 rows=479020 width=26) (actual
> time=2.303..15371.237 rows=479020 loops=1)
> Output: path.pathid, batch.filename
> Buffers: shared hit=2403958 read=7539
> -> Seq Scan on public.batch (cost=0.00..11727.20 rows=479020
> width=85) (actual time=0.340..160.142 rows=479020 loops=1)
> Output: batch.path, batch.filename
> Buffers: shared read=6937
> -> Index Scan using idx_path on public.path (cost=0.56..8.32 rows=1
> width=16) (actual time=0.030..0.031 rows=1 loops=479020)
> Output: path.pathid, path.path
> Index Cond: (path.path = batch.path)
> Buffers: shared hit=2403958 read=602
> Total runtime: 15439.043 ms
>
>
> As you can see, more than twice as fast, and a very high hit ratio on the
> path table, even if we start from a cold cache (I did, here, both
> PostgreSQL and OS). We have an excellent hit ratio because the batch table
> contains few different path (several files in a directory), and is already
> quite clustered, as it comes from a backup, which is of course performed
> directory by directory.
>

What is your effective_cache_size set to?

Cheers,

Jeff