Add cardinality tips to FAQ and sqlserver input (#6852)

docs/FAQ.md

@@ -6,8 +6,8 @@ You will need to setup several volume mounts as well as some environment
 variables:
 ```
 docker run --name telegraf
-        -v /:/hostfs:ro
-        -v /etc:/hostfs/etc:ro
+	-v /:/hostfs:ro
+	-v /etc:/hostfs/etc:ro
 	-v /proc:/hostfs/proc:ro
 	-v /sys:/hostfs/sys:ro
 	-v /var:/hostfs/var:ro
@@ -43,6 +43,33 @@ If running as a service add the environment variable to `/etc/default/telegraf`:
 GODEBUG=netdns=cgo
 ```
 
+### Q: How can I manage series cardinality?
+
+High [series cardinality][], when not properly managed, can cause high load on
+your database.  Telegraf attempts to avoid creating series with high
+cardinality, but some monitoring workloads such as tracking containers are are
+inherently high cardinality.  These workloads can still be monitored, but care
+must be taken to manage cardinality growth.
+
+You can use the following techniques to avoid cardinality issues:
+
+- Use [metric filtering][] options to exclude unneeded measurements and tags.
+- Write to a database with an appropriate [retention policy][].
+- Limit series cardinality in your database using the
+  [max-series-per-database][] and [max-values-per-tag][] settings.
+- Consider using the [Time Series Index][tsi].
+- Monitor your databases using the [show cardinality][] commands.
+- Consult the [InfluxDB documentation][influx docs] for the most up-to-date techniques.
+
+[series cardinality]: https://docs.influxdata.com/influxdb/v1.7/concepts/glossary/#series-cardinality
+[metric filtering]: https://github.com/influxdata/telegraf/blob/master/docs/CONFIGURATION.md#metric-filtering
+[retention policy]: https://docs.influxdata.com/influxdb/latest/guides/downsampling_and_retention/
+[max-series-per-database]: https://docs.influxdata.com/influxdb/latest/administration/config/#max-series-per-database-1000000
+[max-values-per-tag]: https://docs.influxdata.com/influxdb/latest/administration/config/#max-values-per-tag-100000
+[tsi]: https://docs.influxdata.com/influxdb/latest/concepts/time-series-index/
+[show cardinality]: https://docs.influxdata.com/influxdb/latest/query_language/spec/#show-cardinality
+[influx docs]: https://docs.influxdata.com/influxdb/latest/
+
 ### Q: When will the next version be released?
 
 The latest release date estimate can be viewed on the