osmium-index-types (5)
NAME
osmium-index-types - Index types used to store node locations
DESCRIPTION
The osmium add-locations-to-ways and osmium export commands have to keep an index of the node locations in memory or in a temporary file on disk while doing their work. There are several different ways this can be done which have different advantages and disadvantages.
Use the --show-index-types/-I option on these commands to show all available index types. It depends on your operating system which index types are available.
Use the --index-type/-i option on these commands to set the index type to be used.
The default index type is flex_mem which will keep all
data in memory and works for small extracts as well as the whole planet
file. It is the right choice for almost all use cases if you have enough
memory to keep the whole index in memory.
For the osmium export command, the special type
none is used when reading from files with the node
locations on the ways. (See osmium-add-node-locations-to-ways(1)
for how to get a file like this.)
You can use one of the file-based indexes for the node location store
to minimize memory use, but performance will suffer. In this case use
sparse_file_array if you have a small or medium sized
extract and dense_file_array if you are working with a full
planet or a really large extract.
When using the file-based index types (*_file_array),
add the filename you want to use for the index after a comma to the
index types like so:
... -i dense_file_array,index.dat ...
MEMORY USE
It depends on the index type used how much memory is needed:
- For
sparse_*_arraytypes 16 bytes per node in the input file are used. - For
dense_*_arraytypes 8 bytes times the largest node ID in the input file are used.
The *_mem_* types use potentially up to twice this
amount.
The *mem* and *mmap* types store the data
in memory, the *file* types in a file on disk.
The flex_mem type automatically switches between
something similar to sparse_mmap_array for smaller extracts
and dense_mmap_array for larger extracts or the whole
planet file.
If you specify the --verbose/-v option, Osmium will display how much memory was used for the index.