Remove xid_to_int4 postgres function

Fixes #3288

CONFIGURE.md

@@ -129,5 +129,4 @@ If you want to deploy The Rails Port for production use, you'll need to make a f
 * The included version of the map call is quite slow and eats a lot of memory. You should consider using [CGIMap](https://github.com/zerebubuth/openstreetmap-cgimap) instead.
 * Make sure you generate the i18n files and precompile the production assets: `RAILS_ENV=production rake i18n:js:export assets:precompile`
 * Make sure the web server user as well as the rails user can read, write and create directories in `tmp/`.
-* If you want to use diff replication then you might want to consider installing the shared library special SQL functions for the `xid_to_int4` function. A pure SQL version is available, but may become a performance issue on large databases with a high rate of changes. Note that you will need a version of PostgreSQL < 9.6 (yes, _less than_) to use `xid` indexing, whether pure SQL or shared library.
 * If you expect to serve a lot of `/changes` API calls, then you might also want to install the shared library versions of the SQL functions.

INSTALL.md

@@ -278,7 +278,6 @@ Then we create the functions within each database. We're using `pwd` to substitu
 
 ```
 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"
 ```
 
 # Ruby development install and versions<a name="rbenv"></a> (optional)

db/functions/Makefile

@@ -16,7 +16,7 @@ all: ${DESTDIR}/libpgosm.so
 clean:
 	$(RM) ${DESTDIR}/*.so ${DESTDIR}/*.o
 
-${DESTDIR}/libpgosm.so: ${DESTDIR}/quadtile.o ${DESTDIR}/xid_to_int4.o
+${DESTDIR}/libpgosm.so: ${DESTDIR}/quadtile.o
 	cc ${LDFLAGS} -o $@ $^
 
 ${DESTDIR}/%.o: %.c

db/functions/functions.sql

@@ -40,34 +40,3 @@ BEGIN
   RETURN (x << 1) | y;
 END;
 $$ LANGUAGE plpgsql IMMUTABLE;
-
-
--- xid_to_int4 converts a PostgreSQL transaction ID (xid) to a 32-bit integer
--- which can then be used to efficiently find rows which have changed between
--- two given transactions. This is currently used by Osmosis to extract a
--- stream of edits for "diff replication" **HOWEVER** this is a pain point, as
--- (ab)using the xid in this way is _not_ supported or recommended by Postgres
--- devs. It is preventing us upgrading to PostgreSQL version 10+, and will
--- hopefully be replaced Real Soon Now.
---
--- From the Osmosis distribution by Brett Henderson:
--- https://github.com/openstreetmap/osmosis/blob/master/package/script/contrib/apidb_0.6_osmosis_xid_indexing.sql
-CREATE OR REPLACE FUNCTION xid_to_int4(t xid)
-  RETURNS integer
-  AS
-$$
-DECLARE
-  tl bigint;
-  ti int;
-BEGIN
-  tl := t;
-
-  IF tl >= 2147483648 THEN
-    tl := tl - 4294967296;
-  END IF;
-
-  ti := tl;
-
-  RETURN ti;
-END;
-$$ LANGUAGE 'plpgsql' IMMUTABLE STRICT;

db/functions/xid_to_int4.c

@@ -1,22 +0,0 @@
-#include <postgres.h>
-#include <fmgr.h>
-
-Datum
-xid_to_int4(PG_FUNCTION_ARGS)
-{
-   TransactionId xid = PG_GETARG_INT32(0);
-
-   PG_RETURN_INT32(xid);
-}
-
-PG_FUNCTION_INFO_V1(xid_to_int4);
-
-/*
- * To bind this into PGSQL, try something like:
- *
- * CREATE FUNCTION xid_to_int4(xid) RETURNS int4
- *  AS '/path/to/rails-port/db/functions/libpgosm', 'xid_to_int4'
- *  LANGUAGE C IMMUTABLE STRICT;
- *
- * (without all the *s)
- */

db/structure.sql

@@ -147,34 +147,6 @@ END;
 $$;
 
 
---
--- Name: xid_to_int4(xid); Type: FUNCTION; Schema: public; Owner: -
---
-
-CREATE FUNCTION public.xid_to_int4(t xid) RETURNS integer
-    LANGUAGE plpgsql IMMUTABLE STRICT
-    AS $$
-DECLARE
-  tl bigint;
-  ti int;
-BEGIN
-  tl := t;
-
-  IF tl >= 2147483648 THEN
-    tl := tl - 4294967296;
-  END IF;
-
-  ti := tl;
-
-  RETURN ti;
-END;
-$$;
-
-
-SET default_tablespace = '';
-
-SET default_table_access_method = heap;
-
 --
 -- Name: acls; Type: TABLE; Schema: public; Owner: -
 --

script/vagrant/setup/provision.sh

@@ -53,7 +53,6 @@ sudo -u vagrant psql -d openstreetmap -f db/functions/functions.sql
 #pushd db/functions
 #sudo -u vagrant make
 #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