fix(backend): change names of exception columns

change column name of `exception.exceptions` & `exception.threads`
to `exception_exceptions` & `exception_threads` as clickhouse otherwise
treats the dot separated fields as a nested data structure (because the
value are arrays) and tries to put `SIZES_OF_ARRAYS_DONT_MATCH` constraints.
what we desire here is not a nested field but rather 2 separate fields that
facilitates simple writes & reads.

closes #46

measure-backend/measure-go/events.go

@@ -56,8 +56,8 @@ var columns = []string{
 	"resource.measure_sdk_version",
 	"exception.thread_name",
 	"exception.handled",
-	"exception.exceptions",
-	"exception.threads",
+	"exception_exceptions",
+	"exception_threads",
 	"string.severity_text",
 	"string.string",
 	"gesture_long_click.target",
@@ -116,7 +116,23 @@ type Frame struct {
 }
 
 func (f *Frame) encode() string {
-	return fmt.Sprintf("(%d, %d, '%s', '%s', '%s', '%s')", f.LineNum, f.ColNum, f.ModuleName, f.FileName, f.ClassName, f.MethodName)
+	moduleName := f.ModuleName
+	fileName := f.FileName
+	className := f.ClassName
+	methodName := f.MethodName
+	if f.ModuleName == "" {
+		moduleName = "__blank__"
+	}
+	if f.FileName == "" {
+		fileName = "__blank__"
+	}
+	if f.ClassName == "" {
+		className = "__blank__"
+	}
+	if f.MethodName == "" {
+		methodName = "__blank__"
+	}
+	return fmt.Sprintf("(%d, %d, '%s', '%s', '%s', '%s')", f.LineNum, f.ColNum, moduleName, fileName, className, methodName)
 }
 
 type Frames []Frame

measure-backend/sql-statements/clickhouse/create-events-table-2.sql

@@ -28,8 +28,9 @@ create table if not exists events_test_2
     /* exceptions */
     `exception.thread_name` LowCardinality(String),
     `exception.handled` Bool,
-    `exception.exceptions` Array(Tuple(LowCardinality(String), LowCardinality(String), Array(Tuple(Int32, Int32, LowCardinality(String), LowCardinality(String), LowCardinality(String), LowCardinality(String))))),
-    `exception.threads` Array(Tuple(LowCardinality(String), Array(Tuple(Int32, Int32, LowCardinality(String), LowCardinality(String), LowCardinality(String), LowCardinality(String))))),
+    /* uses undescore because clickhouse treats dot as a nested data structure and tries to match the length of exception.exceptions & exception.threads */
+    `exception_exceptions` Array(Tuple(LowCardinality(String), LowCardinality(String), Array(Tuple(Int32, Int32, LowCardinality(String), LowCardinality(String), LowCardinality(String), LowCardinality(String))))),
+    `exception_threads` Array(Tuple(LowCardinality(String), Array(Tuple(Int32, Int32, LowCardinality(String), LowCardinality(String), LowCardinality(String), LowCardinality(String))))),
     /* string */
     `string.severity_text` LowCardinality(FixedString(10)),
     `string.string` String,