On 22/02/10 12:39, Peter Körner wrote:
So we're nearly done, we're sth. around one
hour behind the main DB.
Great, but again it seems rather slow.
The problem is, that the "Going over pending ways / relations" phase
takes too long for small window sizes.
Importing 2 Minutes of changes takes around 15 seconds for the
"Processing: Node(k) Way(k) Relation(k)" phase and 5 minutes for the
"Going over pending.." phase. That's just too long.
The "Going over pending.." phase amongst others executes a SELECT id FROM
planet_osm_ways WHERE pending; which seems to require a seq_scan on planet_osm_ways.
However, a single seq scan on ways seems to take on the order of 8 minutes in my
Likewise, seq_scans on the other tables also take very long. A sec_scan on
planet_osm_point takes about a minute, on planet_osm_polygon about 3 minutes and
on planet_osm_line it seems to take over ten minutes for a single seq_scan.
Given that for low zoom levels (before the spatial indices kick in), there are
several queries per tile requiring full table scans, this doesn't look good for
rendering performance. I don't have any comparison numbers from other servers
that have the full planet loaded to see if that is normal, but perhaps we can do
some comparisons with cassini?
P.S. there does seem to be an index on "pending" but trying to run some queries
from psql, it didn't seem to be used.
I'm constantly adjusting the window size to find the best match between
runtime and window size but as I'd like to have a 1 minute window, as we
have it on cassini, we'll need to tweak a little somewhere.
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