X-Git-Url: https://git.openstreetmap.org/rails.git/blobdiff_plain/783b5e3729228908d7404ae7404af1023501a906..18c5e1622577374cdd4535d2f06e9d51226ee974:/CONFIGURE.md

diff --git a/CONFIGURE.md b/CONFIGURE.md
index 91a64119e..278d1c398 100644
--- a/CONFIGURE.md
+++ b/CONFIGURE.md
@@ -131,3 +131,5 @@ If you want to deploy The Rails Port for production use, you'll need to make a f
 * The included version of the GPX importer is slow and/or completely inoperable. You should consider using [the high-speed GPX importer](https://git.openstreetmap.org/gpx-import.git/).
 * 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.