Enables InfluxDB TSI data storage as default

See https://docs.influxdata.com/influxdb/v1.7/concepts/time-series-index/
and https://docs.influxdata.com/influxdb/v1.7/concepts/tsi-details/
for details.

Change-Id: Id0daa331378473cb2629228f323d5bc01cb80750

devstack/files/influxdb/influxdb.conf

@@ -58,6 +58,7 @@
   # recreated at startup.  A value of "tsi1" will use a disk based index that supports higher
   # cardinality datasets.
   # index-version = "inmem"
+  index-version = "tsi1"
 
   # Trace logging provides more verbose output around the tsm engine. Turning
   # this on can provide more useful output for debugging tsm engine issues.

doc/source/admin/index.rst

@@ -62,3 +62,13 @@ Provide the following alongside the story:
 2. The fingerprint shown in the error message.
 
 3. The output of ``monasca_db fingerprint --raw``.
+
+Time Series Databases Setup
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Enabling InfluxDB Time Series Index in existing deployments
+-----------------------------------------------------------
+
+If enabling TSI on an existing InfluxDB install please follow the instructions
+for migrating existing data here:
+https://docs.influxdata.com/influxdb/v1.7/administration/upgrading/#upgrading-influxdb-1-3-1-4-no-tsi-preview-to-1-7-x-tsi-enabled

releasenotes/notes/enable-disk-tsi-40f29262a0301531.yaml

@@ -0,0 +1,8 @@
+---
+upgrade:
+  - |
+    Changes InfluxDB data from in-memory to disk storage
+    (see https://docs.influxdata.com/influxdb/v1.7/concepts/time-series-index/).
+    If upgrading an existing InfluxDB install please follow the instructions
+    for migrating existing data here:
+    https://docs.influxdata.com/influxdb/v1.7/administration/upgrading/#upgrading-influxdb-1-3-1-4-no-tsi-preview-to-1-7-x-tsi-enabled