[gdal-dev] OSM Driver and World Planet file (pbf format)

[Even Rouault]

Selon Rahkonen Jukka <Jukka.Rahkonen at mmmtike.fi>:

Interesting results. I'll wait a bit for your tests with SSD to turn
OSM_COMPRESS_NODES to YES. Even if doesn't bring clear advantages, I don't think
it would hurt a lot, because the extra CPU load introduced by the
compression/decompression shouldn't be that high (the compression algorithm used
is just encoding in Protocol Buffer of the differences of longitude/latitude
between consecutive nodes, by chunk of 64 nodes)

Just a word of caution to remind you that the temporary node DB will be written
in the directory pointed by the CPL_TMPDIR config. option/env. variable if
defined, if not defined in TMPDIR, if not defined in TEMP, if not defined in the
current directory form which ogr2ogr is started. In Windows system, the TEMP
env. variable is generally defined, so when you test with your USB external
driver, it is very likely that the node DB is written in the temporary directory
associated with your Windows account.

As far as CPU load is concerned, the conversion is a single-threaded processus,
so on a 8 core system, it is expected that it tops at 100 / 8 = 12,5 % of the
global CPU power. With which hardware configuration and input PBF file do you
manage to reach 100% CPU ? Is that load constant during the process : I imagine
that it could change according to the stage of the conversion.
There might be a potential for parallelizing some stuff. What comes in mind for
now would be PBF decoding (when profiling only PBF decoding, the gzip
decompression is the major CPU user, but not sure if it matters that much in a
real-life ogr2ogr job) or way resolution (currently, we group ways into a batch
until 1 million nodes or 75 000 ways have to be resolved, which leads to more
efficient search in the node DB since we can sort nodes by increasing ids and
avoid useless seeks). But that's not obviously immediate which would lead to
increased efficiently. Parallelization may also generally requires more RAM if
you need work buffers for each thread.

> Even Rouault wrote:
> >
> >
> > > Another set of tests with a brand new and quite powerful laptop.
> > >  Specs for the
> > > computer:
> > > Intel i7-2760QM @2.4 GHz processor (8 threads) Hitachi Travelstar
> > > Z7K320 7200 rpm SATA disk
> > > 8 GB of memory
> > > Windows 7, 64-bit
> > >
> > > GDAL-version r24717, Win64 build from gisinternals.com
> > >
> > > Timings for germany.osm.pbf (1.3 GB)
> > > ====================================
> > >
> > > A) Default settings with command
> > > ogr2ogr -f sqlite -dsco spatialite=yes germany.sqlite germany.osm.pbf
> > > -gt 20000 -progress --config OGR_SQLITE_SYNCHRONOUS OFF
> > >
> > > - reading the data               67 minutes
> > > - creating spatial indexes       38 minutes
> > > - total                         105 minutes
> > >
> > > B) Using in-memory Spatialite db for the first step by giving SET
> > > OSM_MAX_TMPFILE_SIZE=7000
> > >
> > > - reading the data              16 minutes
> > > - creating spatial indexes      38 minutes
> > > - total                         54 minutes
> > >
> > > Peak memory usage during this conversion was 4.4 GB.
> > >
> > > Conclusions
> > > ===========
> > > * The initial reading of data is heavily i/o bound. This phase is
> > > really fast if there is enough memory for keeping the OSM tempfile in
> > > memory but SSD disk seems to offer equally good performance.
> > > * Creating spatial indexes for the Spatialite tables is also i/o
> > > bound. The hardware sets the speed limit and there are no other tricks
> > > for improving the performance. Multi-core CPU is quite idle during
> > > this phase with 10-15% load.
> > > * If user does not plan to do spatial queries then then it may be
> > > handy to save some time and create the Spatialite db without spatial
> > > indexes by using -lco SPATIAL_INDEX=NO option.
> > > * Windows disk i/o may be a limiting factor.
> > >
> > > I consider that for small OSM datasets the speed starts to be good
> > > enough. For me it is about the same if converting the Finnish OSM data
> > > (137 MB in .pbf format) takes 160 or 140 seconds when using the
> > > default settings or in-memory temporary database, respectively.
> >
> > Interesting findings.
> >
> > A SSD is of course the ideal hardware to get efficient random access to the
> > nodes.
> >
> > I've just introduced inr 24719 a new config. option OSM_COMPRESS_NODES
> > that can be set to YES. The effect is to use a compression algorithm while
> > storing the temporary node DB.  This can compress to a factor of 3 or 4,
> and
> > help keeping the node DB to a size where it is below the RAM size and that
> > the OS can dramatically cache it (at least on Linux). This can be efficient
> for
> > OSM extracts of the size of the country, but probably not for a planet
> file. In
> > the case of Germany and France, here's the effect on my PC (SATA disk) :
> >
> > $ time ogr2ogr -f null null /home/even/gdal/data/osm/france_new.osm.pbf
> > - progress --config OSM_COMPRESS_NODES YES [...]
> > real    25m34.029s
> > user    15m11.530s
> > sys 0m36.470s
> >
> > $ time ogr2ogr -f null null /home/even/gdal/data/osm/france_new.osm.pbf
> > - progress --config OSM_COMPRESS_NODES NO [...]
> > real    74m33.077s
> > user    15m38.570s
> > sys 1m31.720s
> >
> > $ time ogr2ogr -f null null /home/even/gdal/data/osm/germany.osm.pbf -
> > progress --config OSM_COMPRESS_NODES YES [...]
> > real    7m46.594s
> > user    7m24.990s
> > sys 0m11.880s
> >
> > $ time ogr2ogr -f null null /home/even/gdal/data/osm/germany.osm.pbf -
> > progress --config OSM_COMPRESS_NODES NO [...]
> > real    108m48.967s
> > user    7m47.970s
> > sys 2m9.310s
> >
> > I didn't turn it to YES by default, because I'm unsure of the performance
> > impact on SSD. Perhaps you have a chance to test.
>
> I cannot test with SSD before weekend but otherwise the new configuration
> option really makes difference in some circumstances.
>
> I have ended up to use the following base command  in speed tests:
> ogr2ogr -f SQLite -dsco spatialite=yes germany.sqlite germany.osm.pbf -gt
> 20000 -progress --config OGR_SQLITE_SYNCHRONOUS -lco SPATIAL_INDEX=NO
>
> Writing into Spatialite is pretty fast with these options and even your null
> driver does not seem to be very much faster. What happens after this step
> (like creating indexes) has nothing to do with OSM driver.
>
> Test with  Intel i7-2760QM @2.4 GHz processor,  7200 rpm SATA disk and 1.3 GB
> input file 'germany.osm.pbf'
> --config OSM_COMPRESS_NODES NO
> 67 minutes
> --config OSM_COMPRESS_NODES YES
> 15 minutes
>
> It means 52 minutes less time or 4.5 times more speed.
> Out of curiosity I tried what happens if I do the whole file input/output by
> using a 2.5" external USB 2.0 drive.
> 19 minutes!
>
> I made also a few tests with an old and much slower Windows computer.
> Running osm2pgsql with Finnish OSM data with that machine takes nowadays
> about 3 hours.
>
> Test with a single Intel Xeon @2.4 GHz processor and the same external USB
> 2.0 disk than in previous test
> Input file 'finland.osm.pbf' 122 MB
> Result: 7 minutes for both  OSM_COMPRESS_NODES NO and OSM_COMPRESS_NODES YES
> Input file 'germany.osm.pbf' 1.3 GB
> Result: 112 minutes with OSM_COMPRESS_NODES YES
>
> Conclusions:
> * When input file has reached the limit where disk i/o  cannot utilize cache
> properly, the compress_nodes setting can have a huge effect.
> * When i/o works well the temporary database storage does not have great
> effect on overall speed. In-memory db, SSD drive and fast SATA drive are all
> equally fast and even external USB 2.0 drive is almost as fast.
> * With small input data file size compress_node setting does not seem to have
> much effect on speed.
> * Obviously CPU is now the limiting factor.
> * OGR OSM driver runs pretty well also on older computers.
> * While single processor PC runs at 100% CPU load the 8-core PC shows only
> 12%.  There seems to be 88% of computing power free for making the memory and
> SSD lines saturated sometimes in the future...
> * Instead of buying expensive hardware like SSD the lucky ones may meet
> someone like Even who wants and can write fast programs.
>
> I found my first notes from less than two weeks  ago when I believed that OSM
> driver was fast.  Now I repeated those tests with same data and same
> computers and the progress I can see is non-negligible. Result in these tests
> is Spatialite db with spatial indexes.
>
> finland.osm.pbf         40 minutes -> 7 minutes
> germany.osm.pbf     15 hours     -> 50 minutes
>
> -Jukka Rahkonen-
>
>
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