From: Matt Amos <zerebubuth@gmail.com>
Date: Fri, 4 Oct 2019 12:09:32 +0000 (+0100)
Subject: Remove need for shared library PostgreSQL functions
X-Git-Tag: live~2952^2~4
X-Git-Url: https://git.openstreetmap.org./rails.git/commitdiff_plain/ced8ac86abac9c9efad7b74a0efe2e252ddc59af?hp=1d7e4a4c467c0efde921955bb7e1337ea48df622

Remove need for shared library PostgreSQL functions

This repo contains code for three functions to be loaded into PostgreSQL as a shared library:

1. `maptile_for_point`, which is used only by the `/changes` API call. This API call is little-used and IMHO should be deprecated and removed. However, even now it's hardly on the hot path for most development activities.
2. `tile_for_point`, which is used only in migrations. At this point, it seems unlikely that anyone will be doing a migration on existing data which would call this function (most developers will be running migrations on an empty database, to set it up).
3. `xid_to_int4`, which is only used for replication using Osmosis and isn't used in the Rails code at all. Hopefully this will be replaced Real Soon Now, but until then it's a quite advanced feature that most developers won't need.

Therefore, this patch proposes to replace the above three shared library functions with SQL implementations of the first two. These are _much_ slower - by a factor of about 30x, however this makes no difference when they're run on a completely empty database. In return, we're able to drop a dependency on the PostgreSQL server development package, and clean a few lines out of the installation instructions.

It's still possible to make and install the shared library functions, and I've included instructions about how to do that - although it shouldn't be necessary for the vast majority of `openstreetmap-website` developers.
---

diff --git a/.travis.yml b/.travis.yml
index e4c81e4c1..7137c2268 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -19,11 +19,7 @@ before_script:
   - sed -e "/idle_in_transaction_session_timeout/d" -e 's/ IMMUTABLE / /' -e "s/AS '.*libpgosm.*',/AS 'libpgosm',/" -e "/^--/d" db/structure.sql > db/structure.expected
   - psql -U postgres -c "CREATE DATABASE openstreetmap"
   - psql -U postgres -c "CREATE EXTENSION btree_gist" openstreetmap
-  - make -C db/functions libpgosm.so
-  - ln db/functions/libpgosm.so /tmp
-  - psql -U postgres -c "CREATE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4 AS '/tmp/libpgosm', 'maptile_for_point' LANGUAGE C STRICT" openstreetmap
-  - psql -U postgres -c "CREATE FUNCTION tile_for_point(int4, int4) RETURNS int8 AS '/tmp/libpgosm', 'tile_for_point' LANGUAGE C STRICT" openstreetmap
-  - psql -U postgres -c "CREATE FUNCTION xid_to_int4(xid) RETURNS int4 AS '/tmp/libpgosm', 'xid_to_int4' LANGUAGE C STRICT" openstreetmap
+  - psql -U postgres -f db/functions/functions.sql openstreetmap
   - cp config/travis.database.yml config/database.yml
   - cp config/example.storage.yml config/storage.yml
   - touch config/settings.local.yml
diff --git a/INSTALL.md b/INSTALL.md
index 2b1b4b5de..641d1160a 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -31,8 +31,8 @@ sudo apt-get update
 sudo apt-get install ruby2.5 libruby2.5 ruby2.5-dev bundler \
                      libmagickwand-dev libxml2-dev libxslt1-dev nodejs \
                      apache2 apache2-dev build-essential git-core phantomjs \
-                     postgresql postgresql-contrib libpq-dev postgresql-server-dev-all \
-                     libsasl2-dev imagemagick libffi-dev libgd-dev libarchive-dev libbz2-dev
+                     postgresql postgresql-contrib libpq-dev libsasl2-dev \
+                     imagemagick libffi-dev libgd-dev libarchive-dev libbz2-dev
 sudo gem2.5 install bundler
 ```
 
@@ -46,7 +46,7 @@ For Fedora, you can install the minimum requirements with:
 sudo dnf install ruby ruby-devel rubygem-rdoc rubygem-bundler rubygems \
                  libxml2-devel js \
                  gcc gcc-c++ git \
-                 postgresql postgresql-server postgresql-contrib postgresql-devel \
+                 postgresql postgresql-server postgresql-contrib \
                  perl-podlators ImageMagick libffi-devel gd-devel libarchive-devel \
                  bzip2-devel nodejs-yarn
 ```
@@ -174,20 +174,12 @@ psql -d openstreetmap -c "CREATE EXTENSION btree_gist"
 
 ### PostgreSQL Functions
 
-We need to install special functions into the PostgreSQL databases, and these are provided by a library that needs compiling first.
+There are special database functions required by a (little-used) API call, the migrations and diff replication. The former two are provided as *either* pure SQL functions or a compiled shared library. It is recommended that you start with the pure SQL versions, as described below, and only install the compiled shared library if you are running a production server making a lot of `/changes` API calls or need the diff replication functionality.
 
-```
-cd db/functions
-make libpgosm.so
-cd ../..
-```
-
-Then we create the functions within each database. We're using `pwd` to substitute in the current working directory, since PostgreSQL needs the full path.
+If you aren't sure which you need, install the SQL version below.
 
 ```
-psql -d openstreetmap -c "CREATE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4 AS '`pwd`/db/functions/libpgosm', 'maptile_for_point' LANGUAGE C STRICT"
-psql -d openstreetmap -c "CREATE FUNCTION tile_for_point(int4, int4) RETURNS int8 AS '`pwd`/db/functions/libpgosm', 'tile_for_point' LANGUAGE C STRICT"
-psql -d openstreetmap -c "CREATE FUNCTION xid_to_int4(xid) RETURNS int4 AS '`pwd`/db/functions/libpgosm', 'xid_to_int4' LANGUAGE C STRICT"
+psql -d openstreetmap -f db/functions/functions.sql
 ```
 
 ### Database structure
@@ -225,3 +217,42 @@ Note that the OSM map tiles you see aren't created from your local database - th
 # Configuration
 
 After installing this software, you may need to carry out some [configuration steps](CONFIGURE.md), depending on your tasks.
+
+# Installing compiled shared library database functions
+
+You probably only need to do this if you are running a large, production instance of openstreetmap-website.
+
+Before installing the functions, it's necessary to install the PostgreSQL server development packages. On Ubuntu this means:
+
+```
+sudo apt-get install postgresql-server-dev-all
+```
+
+On Fedora:
+
+```
+sudo dnf install postgresql-devel
+```
+
+The library then needs compiling.
+
+```
+cd db/functions
+make libpgosm.so
+cd ../..
+```
+
+If you previously installed the SQL versions of these functions, we'll need to delete those before adding the new ones:
+
+```
+psql -d openstreetmap -c "DROP FUNCTION IF EXISTS maptile_for_point"
+psql -d openstreetmap -c "DROP FUNCTION IF EXISTS tile_for_point"
+```
+
+Then we create the functions within each database. We're using `pwd` to substitute in the current working directory, since PostgreSQL needs the full path.
+
+```
+psql -d openstreetmap -c "CREATE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4 AS '`pwd`/db/functions/libpgosm', 'maptile_for_point' LANGUAGE C STRICT"
+psql -d openstreetmap -c "CREATE FUNCTION tile_for_point(int4, int4) RETURNS int8 AS '`pwd`/db/functions/libpgosm', 'tile_for_point' LANGUAGE C STRICT"
+psql -d openstreetmap -c "CREATE FUNCTION xid_to_int4(xid) RETURNS int4 AS '`pwd`/db/functions/libpgosm', 'xid_to_int4' LANGUAGE C STRICT"
+```
diff --git a/db/functions/functions.sql b/db/functions/functions.sql
new file mode 100644
index 000000000..5ed00ea63
--- /dev/null
+++ b/db/functions/functions.sql
@@ -0,0 +1,70 @@
+--------------------------------------------------------------------------------
+-- SQL versions of the C database functions.
+--
+-- Pure pl/pgsql versions are *slower* than the C versions, and not recommended
+-- for production use. However, they are significantly easier to install, and
+-- require fewer dependencies.
+--------------------------------------------------------------------------------
+
+-- tile_for_point function returns a Morton-encoded integer representing a z16
+-- tile which contains the given (scaled_lon, scaled_lat) coordinate. Note that
+-- these are passed into the function as (lat, lon) and should be scaled by
+-- 10^7.
+--
+-- The Morton encoding packs two dimensions down to one with fairly good
+-- spatial locality, and can be used to index points without the need for a
+-- proper 2D index.
+CREATE OR REPLACE FUNCTION tile_for_point(scaled_lat int4, scaled_lon int4)
+  RETURNS int8
+  AS $$
+DECLARE
+  x int8; -- quantized x from lon,
+  y int8; -- quantized y from lat,
+BEGIN
+  x := round(((scaled_lon / 10000000.0) + 180.0) * 65535.0 / 360.0);
+  y := round(((scaled_lat / 10000000.0) +  90.0) * 65535.0 / 180.0);
+
+  -- these bit-masks are special numbers used in the bit interleaving algorithm.
+  -- see https://graphics.stanford.edu/~seander/bithacks.html#InterleaveBMN
+  -- for the original algorithm and more details.
+  x := (x | (x << 8)) &   16711935; -- 0x00FF00FF
+  x := (x | (x << 4)) &  252645135; -- 0x0F0F0F0F
+  x := (x | (x << 2)) &  858993459; -- 0x33333333
+  x := (x | (x << 1)) & 1431655765; -- 0x55555555
+
+  y := (y | (y << 8)) &   16711935; -- 0x00FF00FF
+  y := (y | (y << 4)) &  252645135; -- 0x0F0F0F0F
+  y := (y | (y << 2)) &  858993459; -- 0x33333333
+  y := (y | (y << 1)) & 1431655765; -- 0x55555555
+
+  RETURN (x << 1) | y;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
+
+
+-- maptile_for_point returns an integer representing the tile at the given zoom
+-- which contains the point (scaled_lon, scaled_lat). Note that the arguments
+-- are in the order (lat, lon), and should be scaled by 10^7.
+--
+-- The maptile_for_point function is used only for grouping the results of the
+-- (deprecated?) /changes API call. Please don't use it for anything else, as
+-- it might go away in the future.
+CREATE OR REPLACE FUNCTION maptile_for_point(scaled_lat int8, scaled_lon int8, zoom int4)
+  RETURNS int4
+  AS $$
+DECLARE
+  lat CONSTANT DOUBLE PRECISION := scaled_lat / 10000000.0;
+  lon CONSTANT DOUBLE PRECISION := scaled_lon / 10000000.0;
+  zscale CONSTANT DOUBLE PRECISION := 2.0 ^ zoom;
+  pi CONSTANT DOUBLE PRECISION := 3.141592653589793;
+  r_per_d CONSTANT DOUBLE PRECISION := pi / 180.0;
+  x int4;
+  y int4;
+BEGIN
+  -- straight port of the C code. see db/functions/maptile.c
+  x := floor((lon + 180.0) * zscale / 360.0);
+  y := floor((1.0 - ln(tan(lat * r_per_d) + 1.0 / cos(lat * r_per_d)) / pi) * zscale / 2.0);
+
+  RETURN (x << zoom) | y;
+END;
+$$ LANGUAGE plpgsql IMMUTABLE;
diff --git a/script/vagrant/setup/provision.sh b/script/vagrant/setup/provision.sh
index c181376c9..5eb49b24e 100644
--- a/script/vagrant/setup/provision.sh
+++ b/script/vagrant/setup/provision.sh
@@ -19,7 +19,7 @@ apt-get upgrade -y
 apt-get install -y ruby2.5 libruby2.5 ruby2.5-dev \
                      libmagickwand-dev libxml2-dev libxslt1-dev nodejs \
                      apache2 apache2-dev build-essential git-core phantomjs \
-                     postgresql postgresql-contrib libpq-dev postgresql-server-dev-all \
+                     postgresql postgresql-contrib libpq-dev \
                      libsasl2-dev imagemagick libffi-dev libgd-dev libarchive-dev libbz2-dev
 gem2.5 install rake
 gem2.5 install --version "~> 1.16.2" bundler
@@ -38,18 +38,29 @@ if [ "$db_user_exists" != "1" ]; then
     sudo -u vagrant psql -c "create extension btree_gist" openstreetmap
     sudo -u vagrant psql -c "create extension btree_gist" osm_test
 fi
-# build and set up postgres extensions
-pushd db/functions
-sudo -u vagrant make
-sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'maptile_for_point' LANGUAGE C STRICT"
-sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION tile_for_point(int4, int4) RETURNS int8 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'tile_for_point' LANGUAGE C STRICT"
-sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION xid_to_int4(xid) RETURNS int4 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'xid_to_int4' LANGUAGE C STRICT"
-popd
+
+
+# install PostgreSQL functions
+sudo -u vagrant psql -d openstreetmap -f db/functions/functions.sql
+################################################################################
+# *IF* you want a vagrant image which supports replication (or perhaps you're
+# using this script to provision some other server and want replication), then
+# uncomment the following lines (until popd) and comment out the one above
+# (functions.sql).
+################################################################################
+#pushd db/functions
+#sudo -u vagrant make
+#sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION maptile_for_point(int8, int8, int4) RETURNS int4 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'maptile_for_point' LANGUAGE C ST#RICT"
+#sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION tile_for_point(int4, int4) RETURNS int8 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'tile_for_point' LANGUAGE C STRICT"
+#sudo -u vagrant psql openstreetmap -c "CREATE OR REPLACE FUNCTION xid_to_int4(xid) RETURNS int4 AS '/srv/openstreetmap-website/db/functions/libpgosm.so', 'xid_to_int4' LANGUAGE C STRICT"
+#popd
+
+
 # set up sample configs
 if [ ! -f config/database.yml ]; then
     sudo -u vagrant cp config/example.database.yml config/database.yml
 fi
 touch config/settings.local.yml
 # migrate the database to the latest version
-sudo -u vagrant rake db:migrate
+sudo -u vagrant bundle exec rake db:migrate
 popd