Serving OSM tiles - mod_tile/renderd/postgresql problem: I sometimes get 404 Not Found

Question

When I request tiles I get sometimes 404 Not Found. Usually, if I request the same tile again it appears alright (with 200 OK).

This is what I found in renderd logs:

renderd[734]: An error occurred while loading the map layer 'default': Postgis Plugin: ERROR: could not open file "base/16386/240582": Interrupted system call
in executeQuery Full sql was: 'SELECT * FROM ( SELECT way, way_area AS area, COALESCE(landuse, leisure, "natural", highway, amenity, tourism) AS type
FROM planet_osm_polygon
WHERE way_area > 100000
ORDER BY way_area DESC
) AS data LIMIT 0'

This is my 000-default.conf:

<VirtualHost *:80>
        # The ServerName directive sets the request scheme, hostname and port that
        # the server uses to identify itself. This is used when creating
        # redirection URLs. In the context of virtual hosts, the ServerName
        # specifies what hostname must appear in the request's Host: header to
        # match this virtual host. For the default virtual host (this file) this
        # value is not decisive as it is used as a last resort host regardless.
        # However, you must set it for any further virtual host explicitly.
        #ServerName www.example.com

        LoadTileConfigFile /usr/local/etc/renderd.conf
        ModTileRenderdSocketName /var/run/renderd/renderd.sock
        # Timeout before giving up for a tile to be rendered
        ModTileRequestTimeout 0
        # Timeout before giving up for a tile to be rendered that is otherwise missing
        ModTileMissingRequestTimeout 600

        ModTileCacheDurationMax 31536000
        ModTileCacheDurationMinimum 31536000
        ModTileMaxLoadMissing 999999999
        ModTileEnableTileThrottling Off
        ModTileBulkMode Off
        TimeOut 600

        ServerAdmin webmaster@localhost
        DocumentRoot /var/www/html

        # Available loglevels: trace8, ..., trace1, debug, info, notice, warn,
        # error, crit, alert, emerg.
        # It is also possible to configure the loglevel for particular
        # modules, e.g.
        #LogLevel info ssl:warn

        ErrorLog ${APACHE_LOG_DIR}/error.log
        CustomLog ${APACHE_LOG_DIR}/access.log combined

        # For most configuration files from conf-available/, which are
        # enabled or disabled at a global level, it is possible to
        # include a line for only one particular virtual host. For example the
        # following line enables the CGI configuration for this host only
        # after it has been globally disabled with "a2disconf".
        #Include conf-available/serve-cgi-bin.conf
        Alias /log/ "/var/log/"
    <Directory "/var/log/">
           Options Indexes MultiViews FollowSymLinks
           AllowOverride None
           Order deny,allow
           Deny from all
           Allow from all
            Require all granted
    </Directory>
</VirtualHost>

My postgresql.conf: https://pastebin.com/veYxsui5

I'm running the setup in Docker container on c5.xlarge instance on AWS.

How to eliminate 404s?

Answer 1

In my experience this means it's taking too long for renderd to do ad hoc rendering and you either need to pre-render most tiles or increase the resources renderd has to work with. You could test this by trying to reproduce the 404 error on tiles that you pre-render. If you can't reproduce it you could infer that the issue is the time it takes to render a new tile.