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From Matthias Käppler <matth...@qype.com>
Subject Improving performance for SOLR geo queries?
Date Mon, 06 Feb 2012 10:47:01 GMT
Hi,

we need to perform fast geo lookups on an index of ~13M places, and
were running into performance problems here with SOLR. We haven't done
a lot of query optimization / SOLR tuning up until now so there's
probably a lot of things we're missing. I was wondering if you could
give me some feedback on the way we do things, whether they make
sense, and especially why a supposed optimization we implemented
recently seems to have no effect, when we actually thought it would
help a lot.

What we do is this: our API is built on a Rails stack and talks to
SOLR via a Ruby wrapper. We have a few filters that almost always
apply, which we put in filter queries. Filter cache hit rate is
excellent, about 97%, and cache size caps at 10k filters (max size is
32k, but it never seems to reach that many, probably because we
replicate / delta update every few minutes). Still, geo queries are
slow, about 250-500msec on average. We send them with cache=false, so
as to not flood the fq cache and cause undesirable evictions.

Now our idea was this: while the actual geo queries are poorly
cacheable, we could clearly identify geographical regions which are
more often queried than others (naturally, since we're a user driven
service). Therefore, we dynamically partition Earth into a static grid
of overlapping boxes, where the grid size (the distance of the nodes)
depends on the maximum allowed search radius. That way, for every user
query, we would always be able to identify a single bounding box that
covers it. This larger bounding box (200km edge length) we would send
to SOLR as a cached filter query, along with the actual user query
which would still be sent uncached. Ex:

User asks for places in 10km around 49.14839,8.5691, then what we will
send to SOLR is something like this:

fq={!bbox cache=false d=10 sfield=location_ll pt=49.14839,8.5691}
fq={!bbox cache=true d=100.0 sfield=location_ll
pt=49.4684836290799,8.31165802979391} <-- this one we derive
automatically

That way SOLR would intersect the two filters and return the same
results as when only looking at the smaller bounding box, but keep the
larger box in cache and speed up subsequent geo queries in the same
regions. Or so we thought; unfortunately this approach did not help
query execution times get better, at all.

Question is: why does it not help? Shouldn't it be faster to search on
a cached bbox with only a few hundred thousand places? Is it a good
idea to make these kinds of optimizations in the app layer (we do this
as part of resolving the SOLR query in Ruby), and does it make sense
at all? We're not sure what kind of optimizations SOLR already does in
its query planner. The documentation is (sorry) miserable, and
debugQuery yields no insight into which optimizations are performed.
So this has been a hit and miss game for us, which is very ineffective
considering that it takes considerable time to build these kinds of
optimizations in the app layer.

Would be glad to hear your opinions / experience around this.

Thanks!

-- 
Matthias Käppler
Lead Developer API & Mobile

Qype GmbH
Großer Burstah 50-52
20457 Hamburg
Telephone: +49 (0)40 - 219 019 2 - 160
Skype: m_kaeppler
Email: matthias@qype.com

Managing Director: Ian Brotherston
Amtsgericht Hamburg
HRB 95913

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