Osm2pgsql Manual

Introduction

Osm2pgsql is used to import OSM data into a PostgreSQL/PostGIS database for rendering into maps and many other uses. Usually it is only part of a toolchain, for instance other software is needed that do that actual rendering (i.e. turning the data into a map), deliver the maps to the user etc.

Osm2pgsql is a fairly complex piece of software and it interacts with the database system and other pieces of the toolchain in complex ways. It will take a while until you get some experience with it. It is strongly recommended that you try out osm2pgsql with small extracts of the OSM data, for instance the data for your city. Do not start with importing data for the whole planet, it is easy to get something wrong and it will break after processing the data for hours or days. You can save yourself a lot of trouble doing some trial runs starting with small extracts and working your way up, observing memory and disk usage along the way.

It helps to be familiar with the PostgreSQL database system and the PostGIS extension to it as well as the SQL database query language. Some knowledge of the Lua language is also useful.

This manual always documents the current version of osm2pgsql. If same information is only valid in certain versions, the section will have a note like this: Version >= 1.4.0

It is recommended that you always use the newest released version of osm2pgsql. Earlier versions sometimes contain bugs that have long since been fixed.

System Requirements

Operating System

Osm2pgsql works on Linux, Windows, and macOS.

Osm2pgsql is developed on Linux and most of the developers don’t have experience with running it on anything but Linux, so it will probably works best there. This documentation is also somewhat geared towards Linux users. That being said, we strive to make the software work on Windows and macOS as well. Please report any problems you might have.

Only 64bit systems are supported.

Read the installation instructions for details on how to install osm2pgsql on your system.

Main Memory

Memory requirements for your system will vary widely depending on the size of your input file. Is it city-sized extract or the whole planet? As a rule of thumb you need at least as much main memory as the PBF file with the OSM data is large. So for a planet file you currently need at least 64 GB RAM. Osm2pgsql will not work with less than 2 GB RAM.

More memory can be used as cache and speed up processing a lot.

Disk

You are strongly encouraged to use a SSD (NVMe if possible) for your database. This will be much faster than traditional spinning hard disks.

Requirements for your system will vary widely depending on

• the amount of data you want to store (city-sized extract or the whole planet?)
• whether or not you want to update the data regularly

Database Software

You need the PostgreSQL database system with the PostGIS extension installed.

Osm2pgsql aims to support all PostgreSQL and PostGIS versions that are currently supported by their respective maintainers. Currently PostgreSQL versions 9.6 and above and PostGIS versions 2.2 and above are supported. PostgreSQL version 11 or above and PostGIS version 2.4 or above is recommended.

In some cases older versions of osm2pgsql have problems with newer database software versions. You should always run the newest released osm2pgsql version which should ensure you get any fixes we have done to make osm2pgsql work well with any PostgreSQL version.

Osm2pgsql does not work with database systems other than PostgreSQL. The PostgreSQL/PostGIS combination is unique in its capabilities and we are using some of their special features. We are not planning to support any other database systems. There are some database systems out there which claim compatibility with PostgreSQL, they might work or they might not work. Please tell us if you have any experience with them.

Lua Scripting Language

Some parts of osm2pgsql require the use of the Lua scripting language. It is highly recommended that you use a version of osm2pgsql with Lua support enabled, because it gives you a much more flexible configuration. If available osm2pgsql can also be compiled using the Lua JIT (just in time) compiler.

Osm2pgsql can also be compiled without Lua support. In that case the pgsql and gazetteer outputs are the only available.

Preparing the Database

Before you can import any OSM data into a database, you need a database.

Installing PostgreSQL/PostGIS

You need the PostgreSQL database software and the PostGIS plugin for the database. Please read the respective documentation on how to install it. On Linux this can almost always be done with the package manager of your distribution.

• PostgreSQL download page
• PostGIS download page

Creating a Database

To create a database that can be used by osm2pgsql follow these steps:

1. Create a database user that osm2pgsql will use. This user doesn’t need any special rights. We’ll use osmuser here.
2. Create a database that osm2pgsql will use belonging to the user you just created. We’ll use osm as a name here.
3. Enable the postgis and hstore extensions in the newly created database.

On a typical Linux system you’ll have a system user called postgres which has admin privileges for the database system. We’ll use that user for these steps.

Here are typical commands used:

sudo -u postgres createuser osmuser
sudo -u postgres createdb --encoding=UTF8 --owner=osmuser osm
sudo -u postgres psql osm --command='CREATE EXTENSION postgis;'
sudo -u postgres psql osm --command='CREATE EXTENSION hstore;'

Security Considerations

Osm2pgsql does not need any special database rights, it doesn’t need superuser status and doesn’t need to create databases or roles. You should create a database user for the specific use by osm2pgsql which should not have any special PostgreSQL privileges.

Any osm2pgsql setup will need a database to work on. You should create this as PostgreSQL superuser and change ownership (with --owner option on the createdb command or an OWNER= clause on the CREATE DATABASE SQL command) to the user osm2pgsql is using. This way the database user that osm2pgsql uses doesn’t need database creation privileges.

Typical osm2pgsql setups need the postgis and hstore extensions to be enabled in the database. To install these you need superuser privileges in the database. Enable them (with CREATE EXTENSION) as PostgreSQL superuser on the database that osm2pgql is using before you run osm2pgsql.

Of course osm2pgsql needs to be able to create tables and write to the database. Usually it can do this as owner of the database created for it. Using the data, on the other hand, doesn’t need any of those rights. So the map rendering software you are using, for instance, usually only needs to read the data. It is recommended that you run these as a different database user, distinct from the database user osm2pgsql is using and only give that user SELECT rights (with the GRANT command).

Version >= 1.4.0 If you are using a security scheme based on database schemas in your database you can use the --middle-schema and --output-pgsql-schema options and the schema table option in the flex output, respectively, to tell osm2pgsql to load data into specific schemas. You have to create those schemas and give them the correct rights before running osm2pgsql.

Encoding

OpenStreetMap data is from all around the world, it always uses UTF-8 encoding. osm2pgsql will write the data as is into the database, so it has to be in UTF-8 encoding, too.

On any modern system the default encoding for new databases should be UTF-8, but to make sure, you can use the -E UTF8 or --encoding=UTF8 options when creating the database for osm2pgsql with createdb.

Tuning the PostgreSQL Server

Usual installs of the PostgreSQL server come with a default configuration that isn’t well tuned for large databases. You will have to change those settings and restart PostgreSQL before running osm2pgsql, otherwise your system will be much slower than needed.

This section is incomplete and possibly not up to date.

You should tune the following parameters in your postgresql.conf file:

shared_buffers = 2GB
maintenance_work_mem = (10GB)
autovacuum_work_mem = 2GB
work_mem = (50MB)
effective_cache_size = (24GB)
synchronous_commit = off
checkpoint_segments = 100 # only for postgresql <= 9.4
max_wal_size = 1GB # postgresql > 9.4
checkpoint_timeout = 10min
checkpoint_completion_target = 0.9

See more in docs on https://nominatim.org/release-docs/latest/admin/Installation/

For details see also the Resource Consumption section in the Server Configuration chapter in the PostgreSQL documentation.

Running osm2pgsql

Basic command line operation

Osm2pgsql can work in one of two ways: Import only or Import and Update.

If you are new to osm2pgsql we recommend you try the import only approach first and use a small extract of the OSM data.

Import only

OSM data is imported once into the database and will not change afterwards. If you want to update the data, you have to delete it and do a full re-import. This approach is used when updates aren’t needed or only happen rarely. It is also sometimes the only option, for instance when you are using extracts for which change files are not available. This is also a possible approach if disk space is tight, because you don’t need to store data needed only for updates.

In this mode osm2pgsql is used with the -c, --create command line option. This is also the default mode. The following command lines are equivalent:

osm2pgsql -c OSMFILE
osm2pgsql --create OSMFILE
osm2pgsql OSMFILE

In case the system doesn’t have much main memory, you can add the -s, --slim and --drop options. In this case less main memory is used, instead more data is stored in the database. This makes the import much slower, though. See chapter XXX for details on these options.

Import and Update

In this approach OSM data is imported once and afterwards updated more or less regularly from OSM change files. OSM offers minutely, hourly, and daily change files. This mode is used when regular updates are desired and change files are available.

In this mode osm2pgsql is used the first time with the -c, --create command line option (this is also the default mode) and, additionally the -s, --slim options. The following command lines are equivalent:

osm2pgsql -c -s OSMFILE
osm2pgsql --create --slim OSMFILE
osm2pgsql --slim OSMFILE

For the update runs the -a, --append and -s, --slim options must be used. The following command lines are equivalent:

osm2pgsql -a -s OSMFILE
osm2pgsql --append --slim OSMFILE

This approach needs more disk space for your database, because all the information necessary for the updates must be stored somewhere.

Getting Help or Version

To get help or the program version run with the following options:

Database connection

In create and append mode you have to tell osm2pgsql which database to access using the following command line options:

Version >= 1.4.0 Instead of specifying a database name with the -d, --database option you can also specify a connection string in the form of a keyword/value connection string (something like host=localhost port=5432 dbname=mydb) or a URI (postgresql://[user[:password]@][netloc][:port][,...][/dbname][?param1=value1&...]) See the PostgreSQL documentation for details.

Processing the OSM data

Osm2pgsql processing can be separated into multiple steps:

1. The Input reads the OSM data from the OSM file.
2. The Middle stores all objects and keeps track of relationships between objects.
3. The Output transforms the data and loads it into the database.

This is, of course, a somewhat simplified view, but it is enough to understand the operation of the program. The following sections will describe each of the steps in more detail.

The Input

Depending on the operational mode your input file is either

• an OSM data file (in create mode), or
• an OSM change file (in append mode)

Usually osm2pgsql will autodetect the file format, but see the -r, --input-reader option below. Osm2pgsql can not work with OSM history files.

See the Appendix C for more information on how to get and prepare OSM data for use with osm2pgsql.

Use of the -b, --bbox option is not recommended; it is a crude way of limiting the amount of data loaded into the database and it will not always do what you expect it to do, especially at the boundaries of the bounding box. If you use it, choose a bounding box that is larger than your actual area of interest. A better option is to create an extract of the data before using osm2pgsql. See Appendix C for options.

The Middle

The middle keeps track of all OSM objects read by osm2pgsql and the relationships between those objects. It knows, for instance, which ways are used by which nodes, or which members a relation has. It also keeps track of all node locations. It information is necessary to build way geometries from way nodes and relation geometries from members and it is necessary when updating data, because OSM change files only contain changes objects themselves and not all the related objects needed for creating an objects geometry.

More details are in its own chapter.

The Outputs

Osm2pgsql imports OSM data into a PostgreSQL database. How it does this is governed by the output (sometimes called a backend). Several outputs for different use cases are available:

The flex Output Version >= 1.3.0

This is the most modern and most flexible output option. If you are starting a new project, use this output. Many future improvements to osm2pgsql will only be available in this output.

Unlike all the other output options there is almost no limit to how the OSM data can be imported into the database. You can decide which OSM objects should be written to which columns in which database tables. And you can define any transformations to the data you need, for instance to unify a complex tagging schema into a simpler schema if that’s enough for your use case.

This output is described in detail in its own chapter.

The pgsql Output

The pgsql output is the original output and the one that most people who have been using osm2pgsql know about. Many tutorials you find on the Internet only describe this output. It is quite limited in how the data can be written to the database, but many setups still use it.

This output comes in two “flavours”: With the original “C transformation” and with the somewhat newer “Lua transformation” which allows some changes to the data before it is imported.

This output is described in detail in its own chapter.

The gazetteer Output

The gazetteer output is a specialized output used for Nominatim only. There is no information in this manual about its use, see the Nominatim documentation for details.

The multi Output

The multi output is deprecated, it will be removed in a future version of osm2pgsql. If you are using it, switch to the flex output as soon as possible.

The null Output

The null output doesn’t write the data anywhere. It is used for testing and benchmarking, not for normal operation.

Here are the command line options pertaining to the outputs (see later chapters for command line options only used for specific outputs):

The Flex Output

Version >= 1.3.0 The flex output appeared first in version 1.3.0 of osm2pgsql.

The Flex output is experimental. Everything in here is subject to change.

The flex output, as the name suggests, allows for a flexible configuration that tells osm2pgsql what OSM data to store in your database and exactly where and how. It is configured through a Lua file which

• defines the structure of the output tables and
• defines functions to map the OSM data to the database data format

Use the -s, --style=FILE option to specify the name of the Lua file.

Unlike the pgsql output, the flex output doesn’t use command line options for configuration, but the Lua config file only.

The Style File

The flex style file is a Lua script. You can use all the power of the Lua language. This description assumes that you are somewhat familiar with the Lua language, but it is pretty easy to pick up the basics and you can use the example config files in the flex-config directory which contain lots of comments to get you started.

All configuration is done through the osm2pgsql object in Lua. It has the following fields and functions:

Osm2pgsql also provides some additional functions in the Lua helper library described in Appendix B.

Defining a table

You have to define one or more tables where your data should end up. This is done with the osm2pgsql.define_table() function or one of the slightly more convenient functions osm2pgsql.define_(node|way|relation|area)_table().

osm2pgsql.define_table(OPTIONS)
osm2pgsql.define_(node|way|relation|area)_table(NAME, COLUMNS[, OPTIONS])

Here NAME is the name of the table, COLUMNS is a list of Lua tables describing the columns as documented below. OPTIONS is a Lua table with options for the table as a whole. When using the define_table() command, the NAME and COLUMNS are specified as options name and columns, respectively.

Each table is either a node table, way table, relation table, or area table. This means that the data for that table comes primarily from a node, way, relation, or area, respectively. Osm2pgsql makes sure that the OSM object id will be stored in the table so that later updates to those OSM objects (or deletions) will be properly reflected in the tables. Area tables are special, they can contain data derived from ways or from relations. Way ids will be stored as is, relation ids will be stored as negative numbers.

With the osm2pgsql.define_table() function you can also define tables that

• don’t have any ids, but those tables will never be updated by osm2pgsql
• take any OSM object, in this case the type of object is stored in an additional char(1) column.
• are in a specific PostgresSQL tablespace (set option data_tablespace) or that get their indexes created in a specific tablespace (set option index_tablespace).
• are in a specific schema (set option schema). Note that the schema has to be created before you start osm2pgsql.

If you are using the osm2pgsql.define_(node|way|relation|area)_table() convenience functions, osm2pgsql will automatically create an id column named (node|way|relation|area)_id, respectively. If you want more control over the id column(s), use the osm2pgsql.define_table() function.

Most tables will have a geometry column. (Currently only zero or one geometry columns are supported.) The types of the geometry column possible depend on the type of the input data. For node tables you are pretty much restricted to point geometries, but there is a variety of options for relation tables for instance.

The supported geometry types are:

By default geometry columns will be created in web mercator (EPSG 3857). To change this, set the projection parameter of the column to the EPSG code you want (or one of the strings latlon(g), WGS84, or merc(ator), case is ignored).

There is one special geometry column type called area. It can be used in addition to a polygon or multipolygon column. Unlike the normal geometry column types, the resulting database type will not be a geometry type, but real. It will be filled automatically with the area of the geometry. The area will be calculated in web mercator, or you can set the projection parameter of the column to 4326 to calculate it with WGS84 coordinates. Other projections are currently not supported.

In addition to id and geometry columns, each table can have any number of “normal” columns using any type supported by PostgreSQL. Some types are specially recognized by osm2pgsql: text, boolean, int2 (smallint), int4 (int, integer), int8 (bigint), real, hstore, and direction. See the “Type conversion” section for details.

Instead of the above types you can use any SQL type you want. If you do that you have to supply the PostgreSQL string representation for that type when adding data to such columns (or Lua nil to set the column to NULL).

In the table definitions the columns are specified as a list of Lua tables with the following keys:

All the osm2pgsql.define*table() functions return a database table object. You can call the following functions on it:

Processing callbacks

You are expected to define one or more of the following functions:

They all have a single argument of type table (here called object) and no return value. If you are not interested in all object types, you do not have to supply all the functions.

These functions are called for each new or modified OSM object in the input file. No function is called for deleted objects, osm2pgsql will automatically delete all data in your database tables that derived from deleted objects. Modifications are handled as deletions followed by creation of a “new” object, for which the functions are called.

The parameter table (object) has the following fields and functions:

These are only available if the -x|--extra-attributes option is used and the OSM input file actually contains those fields.

You can do anything in those processing functions to decide what to do with this data. If you are not interested in that OSM object, simply return from the function. If you want to add the OSM object to some table call the add_row() function on that table:

-- definition of the table:
table_pois = osm2pgsql.define_node_table('pois', {
    { column = 'tags', type = 'hstore' },
    { column = 'name', type = 'text' },
    { column = 'geom', type = 'point' },
})
...
function osm2pgsql.process_node(object)
...
    table_pois:add_row({
        tags = object.tags,
        name = object.tags.name,
        geom = { create = 'point' }
    })
...
end

The add_row() function takes a single table parameter, that describes what to fill into all the database columns. Any column not mentioned will be set to NULL.

The geometry column is somewhat special. You have to define a geometry transformation that will be used to transform the OSM object data into a geometry that fits into the geometry column. See the next section for details.

Note that you can’t set the object id, this will be handled for you behind the scenes.

Geometry transformations

Currently these geometry transformations are supported:

• { create = 'point' }. Only valid for nodes, create a ‘point’ geometry.
• { create = 'line' }. For ways or relations. Create a ‘linestring’ or ‘multilinestring’ geometry.
• { create = 'area' } For ways or relations. Create a ‘polygon’ or ‘multipolygon’ geometry.

Some of these transformations can have parameters:

• The line transformation has an optional parameter split_at. If this is set to anything other than 0, linestrings longer than this value will be split up into parts no longer than this value.
• The area transformation has an optional parameter multi. If this is set to false (the default), a multipolygon geometry will be split up into several polygons. If this is set to true, the multipolygon geometry is kept as one. It depends on this parameter whether you need a polygon or multipolygon geometry column.

If no geometry transformation is set, osm2pgsql will, in some cases, assume a default transformation. These are the defaults:

• For node tables, a point column gets the node location.
• For way tables, a linestring column gets the complete way geometry, a polygon column gets the way geometry as area (if the way is closed and the area is valid).

Stages

When processing OSM data, osm2pgsql reads the input file(s) in order, nodes first, then ways, then relations. This means that when the ways are read and processed, osm2pgsql can’t know yet whether a way is in a relation (or in several). But for some use cases we need to know in which relations a way is and what the tags of these relations are or the roles of those member ways. The typical case are relations of type route (bus routes etc.) where we might want to render the name or ref from the route relation onto the way geometry.

The osm2pgsql flex output supports this use case by adding an additional “reprocessing” step. Osm2pgsql will call the Lua function osm2pgsql.select_relation_members() for each added, modified, or deleted relation. Your job is to figure out which way members in that relation might need the information from the relation to be rendered correctly and return those ids in a Lua table with the only field ‘ways’. This is usually done with a function like this:

function osm2pgsql.select_relation_members(relation)
    if relation.tags.type == 'route' then
        return { ways = osm2pgsql.way_member_ids(relation) }
    end
end

Instead of using the helper function osm2pgsql.way_member_ids() which returns the ids of all way members, you can write your own code, for instance if you want to check the roles.

Note that select_relation_members() is called for deleted relations and for the old version of a modified relation as well as for new relations and the new version of a modified relation. This is needed, for instance, to correctly mark member ways of deleted relations, because they need to be updated, too. The decision whether a way is to be marked or not can only be based on the tags of the relation and/or the roles of the members. If you take other information into account, updates might not work correctly.

In addition you have to store whatever information you need about the relation in your process_relation() function in a global variable.

After all relations are processed, osm2pgsql will reprocess all marked ways by calling the process_way() function for them again. This time around you have the information from the relation in the global variable and can use it.

If you don’t mark any ways, nothing will be done in this reprocessing stage.

(It is currently not possible to mark nodes or relations. This might or might not be added in future versions of osm2pgsql.)

You can look at osm2pgsql.stage to see in which stage you are.

You want to do all the processing you can in stage 1, because it is faster and there is less memory overhead. For most use cases, stage 1 is enough.

Processing in two stages can add quite a bit of overhead. Because this feature is new, there isn’t much operational experience with it. So be a bit careful when you are experimenting and watch memory and disk space consumption and any extra time you are using. Keep in mind that:

• All data stored in stage 1 for use in stage 2 in your Lua script will use main memory.
• Keeping track of way ids marked in stage 1 needs some memory.
• To do the extra processing in stage 2, time is needed to get objects out of the object store and reprocess them.
• Osm2pgsql will create an id index on all way tables to look up ways that need to be deleted and re-created in stage 2.

Type conversions

The add_row() command will try its best to convert Lua values into corresponding PostgreSQL values. But not all conversions make sense. Here are the detailed rules:

1. Lua values of type function, userdata, or thread will always result in an error.
2. The Lua type nil is always converted to NULL.
3. If the result of a conversion is NULL and the column is defined as NOT NULL, an error is thrown.
4. The Lua type table is converted to the PostgreSQL type hstore if and only if all keys and values in the table are string values. A Lua table can not be converted to any other PostgreSQL type.
5. For boolean columns: The number 0 is converted to false, all other numbers are true. Strings are converted as follows: "yes", "true", "1" are true; "no", "false", "0" are false, all others are NULL.
6. For integer columns (int2, int4, int8): Boolean true is converted to 1, false to 0. Numbers that are not integers or outside the range of the type result in NULL. Strings are converted to integers if possible otherwise the result is NULL.
7. For real columns: Booleans result in an error, all numbers are used as is, strings are converted to a number, if that is not possible the result is NULL.
8. For direction columns (stored as int2 in the database): Boolean true is converted to 1, false to 0. The number 0 results in 0, all positive numbers in 1, all negative numbers in -1. Strings "yes" and "1" will result in 1, "no" and "0" in 0, "-1" in -1. All other strings will result in NULL.
9. For text columns and any other not specially recognized column types, booleans result in an error and numbers are converted to strings.

If you want any other conversions, you have to do them yourself in your Lua code. Osm2pgsql provides some helper functions for other conversions, see the Lua helper library (Appendix B).

The Pgsql Output

This chapter is incomplete.

The pgsql output is the original output osm2pgsql started with. It was designed for rendering OpenStreetMap data, principally with Mapnik. It is still widely used although it is somewhat limited in how the data can be represented in the database.

If you are starting a new project with osm2pgsql, we recommend you use the flex output instead. The pgsql output will not receive all the new features that the flex output has or will get in the future. (There are a lot of old configs and styles out there that need the pgsql output, though. So it will not go away anytime soon.)

Database Layout

The pgsql output always creates a fixed list of four tables shown in the following table. The PREFIX can be set with the -p, --prefix option, the default is planet_osm.

All tables contain a geometry column named way (which is not the most intuitive name, but it can’t be changed now because of backwards compatibility).

Style file

Some aspects of how the pgsql output converts OSM data into PostgreSQL tables can be configured via a style file. The default style file that is usually installed with osm2pgsql is suitable for rendering the standard OSM Mapnik style or similar styles. It also contains the documentation of the style syntax. With a custom style file, you can control how different object types and tags map to different columns and data types in the database.

The style file is a plain text file containing four columns separated by spaces. As each OSM object is processed it is checked against conditions specified in the first two columns. If they match, processing options from the third and fourth columns are applied.

Possible values for the flags are:

The style file may also contain comments. Any text between a # and the end of the line will be ignored.

Special ‘tags’

There are several special values that can be used in the tag column (second column) of the style file for creating additional fields in the database which contain things other than tag values.

To use these, you must use the command line option --extra-attributes when importing.

Schemas and Tablespaces

Usually all tables, indexes and functions that the pgsql output creates are in the default public schema and use the default tablespace.

Version >= 1.4.0 You can use the command line option --output-pgsql-schema=SCHEMA to tell osm2pgsql that it should use the specified schema to create the tables, indexes, and functions in. Note that you have to create the schema before running osm2pgsql and make sure the database user was granted the rights to create tables, indexes, and functions in this schema. Read more about schemas in the PostgreSQL documentation.

Sometimes you want to create special PostgreSQL tablespaces and put some tables or indexes into them. Having often used indexes on fast SSD drives, for instance, can speed up processing a lot. There are three command line options that the pgsql output interprets: To set the tablespace for output tables and indexes, use the --tablespace-main-data=TABLESPC and --tablespace-main-index=TABLESPC options, respectively. You can also use the -i, --tablespace-index=TABLESPC option which will set the tablespace for the pgsql output as well as for the middle! Note that it is your job to create the tablespaces before calling osm2pgsql and making sure the disk behind it is large enough.

Coastline Processing

The natural=coastline tag is suppressed by default, even if you import the natural=* key. Many maps get the coastlines from a different source, so it does not need to import them from the input file. You can use the --keep-coastlines parameter to change this behavior if you want coastlines in your database. See the OSM wiki for more information on coastline processing.

Pgsql Output command line options

These are the command line options interpreted by the pgsql output:

Middle

This chapter is incomplete.

The middle keeps track of all OSM objects read by osm2pgsql and the relationships between those objects. It knows, for instance, which ways are used by which nodes, or which members a relation has. It also keeps track of all node locations. It information is necessary to build way geometries from way nodes and relation geometries from members and it is necessary when updating data, because OSM change files only contain changes objects themselves and not all the related objects needed for creating an objects geometry.

Expire

This chapter is incomplete.

When osm2pgsql is processing OSM changes, it can create a list of tiles that will be affected by those changes. This list can later be used to delete any changed tiles you might have cached. Osm2pgsql only creates this list. How to actually expire the tiles it outside the scope of osm2pgsql. Expire only makes sense in append mode.

Advanced Topics

These are some advanced options.

Needs more detail here.

Tips & Tricks

The flex output allows a wide range of configuration options. Here are some extra tips & tricks.

Primary Keys and Unique IDs

It is often desirable to have a unique PRIMARY KEY on database tables. Many programs need this.

There seems to be a natural unique key, the OSM node, way, or relation ID the data came from. But there is a problem with that: Depending on the configuration, osm2pgsql sometimes adds several rows to the output tables with the same OSM ID. This typically happens when long linestrings are split into shorter pieces or multipolygons are split into their constituent polygons, but it can also happen if your Lua configuration file adds two rows to the same table.

If you need unique keys on your database tables there are two options: Using those natural keys and making sure that you don’t have duplicate entries. Or adding an additional ID column. The latter is easier to do and will work in all cases, but it adds some overhead.

Using Natural Keys

To use OSM IDs as primary keys, you have to make sure that

• You only ever add a single row per OSM object to an output table, i.e. do not call add_row multiple times on the same table for the same OSM object.
• osm2pgsql doesn’t split long linestrings into smaller ones. So you can not use the split_at option on the geometry transformation.
• osm2pgsql doesn’t split multipolygons into polygons. So you have to set multi = true on all area geometry transformations.

You probably also want an index on the ID column. If you are running in slim mode, osm2pgsql will create that index for you. But in non-slim mode you have to do this yourself with CREATE UNIQUE INDEX. You can also use ALTER TABLE to make the column an “official” primary key column.

Using an Additional ID Column

PostgreSQL has the somewhat magic “serial” data types. If you use that datatype in a column definition, PostgreSQL will add an integer column to the table and automatically fill it with an autoincrementing value.

In the flex config you can add such a column to your tables with something like this:

...
{ column = 'id', type = 'serial', create_only = true },
...

The create_only tells osm2pgsql that it should create this column but not try to fill it when adding rows (because PostgreSQL does it for us).

You probably also want an index on this column. After the first import of your data using osm2pgsql, use CREATE UNIQUE INDEX to create one. You can also use ALTER TABLE to make the column an “official” primary key column.

Using create_only columns for postprocessed data

Sometimes it is useful to have data in table rows that osm2pgsql can’t create. For instance you might want to store the center of polygons for faster rendering of a label.

To do this define your table as usual and add an additional column, marking it create_only. In our example case the type of the column should be the PostgreSQL type GEOMETRY(Point, 3857), because we don’t want osm2pgsql to do anything special here, just create the column with this type as is.

polygons_table = osm2pgsql.define_area_table('polygons', {
    { column = 'tags', type = 'hstore' },
    { column = 'geom', type = 'geometry' },
    { column = 'center', type = 'GEOMETRY(Point, 3857)', create_only = true },
    { column = 'area', type = 'area' },
})

After running osm2pgsql as usual, run the following SQL command:

UPDATE polygons SET center = ST_Centroid(geom) WHERE center IS NULL;

If you are updating the data using osm2pgsql --append, you have to do this after each update. When osm2pgsql inserts new rows they will always have a NULL value in center, the WHERE condition makes sure that we only do this (possibly expensive) calculation once.