Ok. Actually it would be expected to have those files working directly.
Will have a quick look why that doesn't work and if we can fix that at least for Matomo 4.
Till then try renaming to DBIP-City.mmdb

Hmmm. Okay, I think that this was because I didn't have the GeoIP2 plugin enabled. On activating this it found the file, but the legacy pear plugin didn't see it (because it's an mmdb file now rather than the .dat file that I was replacing?)

edit: Actually, you're right, it has to be a specific name, even with the GeoIP2 plugin activate. This should certainly be in the docs if it's not just going to load any mmdb file from the directory.

On the subject of activating plugins via the UI.

I would have thought that the Plugins and PluginsInstalled would be better placed in the DB or something. I'm configuring matomo with puppet and because our production infrastructure is a load balanced trio of servers, and a separate DB, these interface changes get wiped out by puppet because the file has changed. Matomo have made some concessions to this with the multi_server_environment and enable_general_settings_admin settings in the config file but I think that you need to think you need to go back to the drawing board on this.

Here's an example of what changes in the config file after a puppet run after activating GeoIP2 via the UI:

Notice: /Stage[main]/Profiles::Matomo::Prerequisites/File[config.ini.php]/content: 
--- /usr/local/www/matomo/config/config.ini.php 2020-02-28 14:55:47.165356000 +0000
+++ /tmp/puppet-file20200228-70086-1s4ero4      2020-02-28 15:44:12.727449000 +0000
@@ -8,6 +8,9 @@
 tables_prefix = "matomo_"
 adapter = "MYSQLI"
 
+[Tracker]
+record_statistics = 1
+
 [log]
 log_writers[] = "file"
 
@@ -15,15 +18,20 @@
 disable_merged_assets = 1
 
 [General]
-force_ssl = 1
-multi_server_environment = 1
+maintenance_mode = 0
 enable_trusted_host_check = 0
-enable_general_settings_admin = 0
 proxy_client_headers[] = "HTTP_X_FORWARDED_FOR"
 proxy_host_headers[] = "HTTP_X_FORWARDED_HOST"
 trusted_hosts[] = "piwik.domain.com"
 salt = ""
+force_ssl = 1
+enable_load_data_infile = 1
+session_save_handler = dbtable
+; These settings prevent inconsistent configuration from happening across servers
+multi_server_environment = 1
+enable_general_settings_admin = 0
 
+
 [Plugins]
 Plugins[] = "CorePluginsAdmin"
 Plugins[] = "CoreAdminHome"
@@ -34,6 +42,7 @@
 Plugins[] = "CoreVisualizations"
 Plugins[] = "Proxy"
 Plugins[] = "API"
+Plugins[] = "ExamplePlugin"
 Plugins[] = "Widgetize"
 Plugins[] = "Transitions"
 Plugins[] = "LanguagesManager"
@@ -48,11 +57,11 @@
 Plugins[] = "SEO"
 Plugins[] = "Events"
 Plugins[] = "UserCountry"
-Plugins[] = "GeoIp2"
 Plugins[] = "VisitsSummary"
 Plugins[] = "VisitFrequency"
 Plugins[] = "VisitTime"
 Plugins[] = "VisitorInterest"
+Plugins[] = "ExampleAPI"
 Plugins[] = "RssWidget"
 Plugins[] = "Feedback"
 Plugins[] = "Monolog"
@@ -85,9 +94,8 @@
 Plugins[] = "UserId"
 Plugins[] = "CustomPiwikJs"
 Plugins[] = "DBStats"
-Plugins[] = "ExamplePlugin"
-Plugins[] = "ExampleAPI"
 Plugins[] = "QueuedTracking"
+Plugins[] = "GeoIp2"
 
 [PluginsInstalled]
 PluginsInstalled[] = "Login"

@rick-pri glad it works now if I understand your comment directly. Re plugins in DB we have an issue here: #6063

Can we close this issue or is there anything left?

Hi @tsteur I think that the documentation needs updating to let us know what to name the files. It seems that not just any .mmdb will work, it has to have a specific name. I just extracted mine to be DBIP-City.mmdb which just works, but I wouldn't have known this without the reply from @sgiehl

edit: Although I might have got this working if I had known about the GeoIP2 plugin earlier as I did find references in the code to this and some other names

I updated the FAQ entry to be more explicit and the rest should be already in #6063, so we can close this.