There is a patch for telegraf to support writing to postgres (https://github.com/influxdata/telegraf/pull/3428 https://github.com/influxdata/telegraf/pull/3428)

There is a patch for telegraf to support writing to postgres (https://github.com/influxdata/telegraf/pull/3428 https://github.com/influxdata/telegraf/pull/3428). Grafana 5.3 (currently in beta) has support for filling in previous values for postgres datasource.