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I loaded in PostgreSQL (9.3) OpenStreetMap data for whole europe (400gb). Then I installed a geocoding api (nominatim) that queries the database with gis queries.

My problem is :

This database is queried a few times a day, but because postgres loads the data in its buffer on demand, my first query on a particular gps point is always slow, and I do only one query per GPS point, so it's always slow (like 60sec slow against 100ms when the data is buffered)

.

What could I do here ?

  • I'm using a A6 Azure instance (4 Cores, 28 GB memory, HDD).
  • Server is Ubuntu 14.04.4 LTS
  • Swapping is enabled
  • There is index on the geometry columns queried.
  • The shared buffer is 10GB
  • work mem is 256MB
  • maintenance work mem is 4GB
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  • Set effective_cache_size=21GB, shared_buffers=14GB and maintenance_work_mem=1GB. Try also work_mem=512MB. To improve speed on 400GB of data, partitioning is the way to go. You need indexes that fit in RAM. – pietrop Oct 9 '16 at 9:51
  • What do the queries look like? When you say index on the geometry column, do you mean spatial index? (i.e. do you use postgis?) – dbilid Nov 8 at 15:16
  • @dbilid yes I do. – remi bourgarel Nov 8 at 15:56
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depending on your usage, you could try to partition the data to reduce the scanned data (at 400gb even your indexes are large and heavy to read...) I think it's your best option as working with 400gb tables is heavy even on a very optimized queries... You could also pre-warm the cache with the index data , by issuing some of your queries on frequent gps points or by using something like pg_prewarm

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  • I don't have a lot of control on the data structure :( And I use postgre 9.3 so there is no prewarm. Do you thin prewarm would work here with a 400gb and a 10gb shared buffer ? – remi bourgarel Oct 7 '16 at 9:38
  • Partitions are almost transparent to the application - if there's a good clause to partition by it might work with a couple of triggers... 400gb on 10 gb buffers won't work- you might get part of the index inside... as for pg_prewarm , you can just run a couple of queries yourself if the points you get are not totally random. – cohenjo Oct 8 '16 at 18:49

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