Add LowCardinality host/measurement

Signed-off-by: Nikolaos Karaolidis <nick@karaolidis.com>

Makefile

@@ -1,7 +1,5 @@
 .PHONY: build
 
-COMMIT_HASH=$(shell git rev-parse --short HEAD)
-
 build:
-	CGOENABLED=false GOOS=linux GOARCH=amd64 go build -o clickhouse_${COMMIT_HASH}_amd64 cmd/main.go
-	CGOENABLED=false GOOS=linux GOARCH=arm64 go build -o clickhouse_${COMMIT_HASH}_arm64 cmd/main.go
+	CGOENABLED=false GOOS=linux GOARCH=amd64 go build -o telegraf-clickhouse-plugin-linux-amd64 cmd/main.go
+	CGOENABLED=false GOOS=linux GOARCH=arm64 go build -o telegraf-clickhouse-plugin-linux-arm64 cmd/main.go

README.md

@@ -4,6 +4,22 @@ The ClickHouse output plugin saves Telegraf metric data to a ClickHouse database
 
 The plugin uses Golang's generic "database/sql" interface and third party drivers.
 
+## Build
+
+Dependencies:
+
+* [Go](https://golang.org/doc/install)
+* [Make](https://www.gnu.org/software/make/)
+
+To build the plugin, run `make` in the root directory of the project.
+
+Alternatively, you can build the plugin using Docker:
+
+```bash
+docker run --rm -v $(pwd):/telegraf -w /telegraf -e CGOENABLED=false -e GOOS=linux -e GOARCH=amd64 golang go build -o telegraf-clickhouse-plugin-linux-amd64 cmd/main.go
+docker run --rm -v $(pwd):/telegraf -w /telegraf -e CGOENABLED=false -e GOOS=linux -e GOARCH=arm64 golang go build -o telegraf-clickhouse-plugin-linux-arm64 cmd/main.go
+```
+
 ## Getting started
 
 To use the plugin, set the data source name (DSN). The user account must have privileges to insert rows and create tables.

plugins/outputs/clickhouse/clickhouse.go

@@ -160,10 +160,10 @@ func (ch *ClickHouse) toDatatype(value interface{}) string {
 
 func (ch *ClickHouse) toNullableDatatype(key string, value interface{}) string {
 	datatype := ch.toDatatype(value)
-	if key != "host" && key != ch.TimestampColumn && key != "measurement" {
-		return fmt.Sprintf("Nullable(%s)", datatype)
+	if key == "host" || key == "measurement" {
+		return fmt.Sprintf("LowCardinality(%s)", datatype)
 	}
-	return datatype
+	return fmt.Sprintf("Nullable(%s)", datatype)
 }
 
 func (ch *ClickHouse) pepareMetrics(metrics []telegraf.Metric, metricsData map[string][]map[string]interface{}, columns map[string]*orderedmap.OrderedMap[string, string]) {