Draft: Reduced way node index

Improved version of osm2pgsql-dev#1058

Needs more testing.

docs/bucket-index.md

@@ -0,0 +1,72 @@
+
+# Bucket index for slim mode
+
+Osm2pgsql since version XXX uses an index for way node lookups in slim mode
+that needs a lot less disk space than before. For a planet the savings can be
+about 200 GB! Lookup times are slightly slower, but this shouldn't be an issue
+for most people.
+
+If you are not using slim mode and/or not doing updates of your database, this
+does not apply to you.
+
+Osm2pgsql will **not** update an existing database to the new index.
+
+## Update for normal users
+
+If your database was created with an older version of osm2pgsql you might want
+to start again from an empty database. Just do a reimport and osm2pgsql will
+use the new space-saving index.
+
+## Update for expert users
+
+This is only for users who are very familiar with osm2pgsql and PostgreSQL
+operation. You can break your osm2pgsql database beyond repair if something
+goes wrong here and you might not even notice.
+
+You can create the index yourself by following these steps:
+
+Drop the existing index. Replace `{prefix}` by the prefix you are using.
+Usually this is `planet_osm`:
+
+```
+DROP INDEX {prefix}_ways_nodes_idx;
+```
+
+Create the `index_bucket` function needed for the index. Replace
+`{index_bucket_size}` by the bucket size you want. If you don't have a reason
+to use something else, use `32`:
+
+```
+CREATE FUNCTION index_bucket(int8[]) RETURNS int8[] AS $$
+  SELECT ARRAY(SELECT DISTINCT unnest($1)/{index_bucket_size})
+$$ LANGUAGE SQL IMMUTABLE;
+```
+
+Now you can create the new index. Again, replace `{prefix}` by the prefix
+you are using:
+
+```
+CREATE INDEX ON {prefix}_ways
+  USING GIN (index_bucket(nodes))
+  WITH (fastupdate = off);
+```
+
+If you want to create the index in a specific tablespace you can do this:
+
+```
+CREATE INDEX ON {prefix}_ways
+  USING GIN (index_bucket(nodes))
+  WITH (fastupdate = off) TABLESPACE {tablespace};
+```
+
+## Bucket size (for experts)
+
+When creating a new database (when used in create mode with slim option),
+osm2pgsql will create a bucket index using bucket size 32.
+
+You can set the environment variable `OSM2PGSQL_INDEX_BUCKET_SIZE` to the
+bucket size you want. Values between about 8 and 64 might make sense.
+
+To completely disable the bucket index and create an index compatible with
+earlier versions of osm2pgsql, set `OSM2PGSQL_INDEX_BUCKET_SIZE` to `0`.
+

src/middle-pgsql.cpp

@@ -55,8 +55,8 @@ static std::string build_sql(options_t const &options, char const *templ)
         fmt::arg("unlogged", options.droptemp ? "UNLOGGED" : ""),
         fmt::arg("using_tablespace", using_tablespace),
         fmt::arg("data_tablespace", tablespace_clause(options.tblsslim_data)),
-        fmt::arg("index_tablespace",
-                 tablespace_clause(options.tblsslim_index)));
+        fmt::arg("index_tablespace", tablespace_clause(options.tblsslim_index)),
+        fmt::arg("index_bucket_size", options.index_bucket_size));
 }
 
 middle_pgsql_t::table_desc::table_desc(options_t const &options,
@@ -634,7 +634,8 @@ static table_sql sql_for_nodes() noexcept
     return sql;
 }
 
-static table_sql sql_for_ways() noexcept
+static table_sql sql_for_ways(bool has_bucket_index,
+                              uint8_t index_bucket_size) noexcept
 {
     table_sql sql{};
 
@@ -653,12 +654,31 @@ static table_sql sql_for_ways() noexcept
                         "  SELECT id, nodes, tags"
                         "    FROM {prefix}_ways WHERE id = ANY($1::int8[]);\n";
 
-    sql.prepare_mark = "PREPARE mark_ways_by_node(int8) AS"
-                       "  SELECT id FROM {prefix}_ways"
-                       "    WHERE nodes && ARRAY[$1];\n";
+    if (has_bucket_index) {
+        sql.prepare_mark = "PREPARE mark_ways_by_node(int8) AS"
+                           "  SELECT id FROM {prefix}_ways w"
+                           "    WHERE $1 = ANY(nodes)"
+                           "      AND index_bucket(w.nodes)"
+                           "       && index_bucket(ARRAY[$1]);\n";
+    } else {
+        sql.prepare_mark = "PREPARE mark_ways_by_node(int8) AS"
+                           "  SELECT id FROM {prefix}_ways"
+                           "    WHERE nodes && ARRAY[$1];\n";
+    }
 
-    sql.create_index = "CREATE INDEX ON {prefix}_ways USING GIN (nodes)"
-                       "  WITH (fastupdate = off) {index_tablespace};\n";
+    if (index_bucket_size == 0) {
+        sql.create_index = "CREATE INDEX ON {prefix}_ways USING GIN (nodes)"
+                           "  WITH (fastupdate = off) {index_tablespace};\n";
+    } else {
+        sql.create_index = "CREATE FUNCTION index_bucket(int8[])"
+                           "  RETURNS int8[] AS $$\n"
+                           "  SELECT ARRAY(SELECT DISTINCT"
+                           "    unnest($1)/{index_bucket_size})\n"
+                           "$$ LANGUAGE SQL IMMUTABLE;\n"
+                           "CREATE INDEX ON {prefix}_ways"
+                           "  USING GIN (index_bucket(nodes))"
+                           "  WITH (fastupdate = off) {index_tablespace};\n";
+    }
 
     return sql;
 }
@@ -697,6 +717,14 @@ static table_sql sql_for_relations() noexcept
     return sql;
 }
 
+static bool check_bucket_index(pg_conn_t *db_connection)
+{
+    auto const res = db_connection->query(
+        PGRES_TUPLES_OK, "SELECT relname FROM pg_class WHERE relkind='i' AND "
+                         "relname LIKE '%_ways_index_bucket_idx';");
+    return res.num_tuples() > 0;
+}
+
 middle_pgsql_t::middle_pgsql_t(options_t const *options)
 : m_append(options->append), m_out_options(options),
   m_cache(new node_ram_cache{options->alloc_chunkwise | ALLOC_LOSSY,
@@ -712,8 +740,16 @@ middle_pgsql_t::middle_pgsql_t(options_t const *options)
 
     fmt::print(stderr, "Mid: pgsql, cache={}\n", options->cache);
 
+    bool const has_bucket_index = check_bucket_index(&m_db_connection);
+
+    if (!has_bucket_index && options->append) {
+        fmt::print(stderr, "You don't have a bucket index. See"
+                           " docs/bucket-index.md for details.\n");
+    }
+
     m_tables[NODE_TABLE] = table_desc{*options, sql_for_nodes()};
-    m_tables[WAY_TABLE] = table_desc{*options, sql_for_ways()};
+    m_tables[WAY_TABLE] = table_desc{
+        *options, sql_for_ways(has_bucket_index, options->index_bucket_size)};
     m_tables[REL_TABLE] = table_desc{*options, sql_for_relations()};
 }
 

src/options.cpp

@@ -324,8 +324,45 @@ static osmium::Box parse_bbox(char const *bbox)
     return osmium::Box{minx, miny, maxx, maxy};
 }
 
+template <typename T>
+T get_env_unsigned(char const *var, T default_value)
+{
+    char const *const str = std::getenv(var);
+
+    if (!str) {
+        return default_value;
+    }
+
+    char *end = nullptr;
+    auto val = std::strtoull(str, &end, 10);
+
+    if (*end != '\0') {
+        fmt::print("Warning! Could not parse value of env variable {}.\n"
+                   "         Using default value of {}.\n\n",
+                   var, default_value);
+        return default_value;
+    }
+
+    if (val > std::numeric_limits<T>::max()) {
+        fmt::print("Warning! Value of env variable {} out of range.\n"
+                   "         Using default value of {}.\n\n",
+                   var, default_value);
+        return default_value;
+    }
+
+    return static_cast<T>(val);
+}
+
+void options_t::get_options_from_env()
+{
+    index_bucket_size =
+        get_env_unsigned<uint8_t>("OSM2PGSQL_INDEX_BUCKET_SIZE", 32);
+}
+
 options_t::options_t(int argc, char *argv[]) : options_t()
 {
+    get_options_from_env();
+
     bool help_verbose = false; // Will be set when -v/--verbose is set
 
     int c;

src/options.hpp

@@ -130,7 +130,16 @@ class options_t
 
     std::vector<std::string> input_files;
 
+    /**
+     * Size of buckets used for way node index. Use 0 to disable for backwards
+     * compatibility.
+     */
+    uint8_t index_bucket_size = 32;
+
 private:
+    /// Set advanced options from environment
+    void get_options_from_env();
+
     /**
      * Check input options for sanity
      */