Profiles: simplify profile stack trace representation

opentelemetry/proto/profiles/v1development/profiles.proto

@@ -99,7 +99,7 @@ message ProfilesDictionary {
   // so that _index fields can use 0 to indicate null/unset.
   repeated Mapping mapping_table = 1;
 
-  // Locations referenced by samples via Profile.location_indices.
+  // Locations referenced by samples via Stack.location_indices.
   repeated Location location_table = 2;
 
   // Functions referenced by locations via Line.function_index.
@@ -119,6 +119,9 @@ message ProfilesDictionary {
 
   // Represents a mapping between Attribute Keys and Units.
   repeated AttributeUnit attribute_units = 7;
+
+  // Stacks referenced by samples via Sample.stack_index.
+  repeated Stack stack_table = 8;
 }
 
 // ProfilesData represents the profiles data that can be stored in persistent storage,
@@ -201,18 +204,19 @@ message ScopeProfiles {
 //   information present to determine the original sampled values.
 //
 // - The profile is represented as a set of samples, where each sample
-//   references a sequence of locations, and where each location belongs
+//   references a stack trace which is a list of locations, each belonging
 //   to a mapping.
-// - There is a N->1 relationship from sample.location_id entries to
-//   locations. For every sample.location_id entry there must be a
+// - There is a N->1 relationship from Stack.location_indices entries to
+//   locations. For every Stack.location_indices entry there must be a
 //   unique Location with that index.
 // - There is an optional N->1 relationship from locations to
 //   mappings. For every nonzero Location.mapping_id there must be a
 //   unique Mapping with that index.
 
-// Represents a complete profile, including sample types, samples,
-// mappings to binaries, locations, functions, string table, and additional metadata.
-// It modifies and annotates pprof Profile with OpenTelemetry specific fields.
+// Represents a complete profile, including sample types, samples, mappings to
+// binaries, stacks, locations, functions, string table, and additional
+// metadata. It modifies and annotates pprof Profile with OpenTelemetry
+// specific fields.
 //
 // Note that whilst fields in this message retain the name and field id from pprof in most cases
 // for ease of understanding data migration, it is not intended that pprof:Profile and
@@ -227,51 +231,48 @@ message Profile {
   // The set of samples recorded in this profile.
   repeated Sample sample = 2;
 
-  // References to locations in ProfilesDictionary.location_table.
-  repeated int32 location_indices = 3;
-
-  // The following fields 4-14 are informational, do not affect
+  // The following fields 3-13 are informational, do not affect
   // interpretation of results.
 
   // Time of collection (UTC) represented as nanoseconds past the epoch.
-  int64 time_nanos = 4;
+  int64 time_nanos = 3;
   // Duration of the profile, if a duration makes sense.
-  int64 duration_nanos = 5;
+  int64 duration_nanos = 4;
   // The kind of events between sampled occurrences.
   // e.g [ "cpu","cycles" ] or [ "heap","bytes" ]
-  ValueType period_type = 6;
+  ValueType period_type = 5;
   // The number of events between sampled occurrences.
-  int64 period = 7;
+  int64 period = 6;
   // Free-form text associated with the profile. The text is displayed as is
   // to the user by the tools that read profiles (e.g. by pprof). This field
   // should not be used to store any machine-readable information, it is only
   // for human-friendly content. The profile must stay functional if this field
   // is cleaned.
-  repeated int32 comment_strindices = 8; // Indices into ProfilesDictionary.string_table.
+  repeated int32 comment_strindices = 7; // Indices into ProfilesDictionary.string_table.
 
   // A globally unique identifier for a profile. The ID is a 16-byte array. An ID with
   // all zeroes is considered invalid. It may be used for deduplication and signal
   // correlation purposes. It is acceptable to treat two profiles with different values
   // in this field as not equal, even if they represented the same object at an earlier
   // time.
   // This field is optional; an ID may be assigned to an ID-less profile in a later step.
-  bytes profile_id = 9;
+  bytes profile_id = 8;
 
   // dropped_attributes_count is the number of attributes that were discarded. Attributes
   // can be discarded because their keys are too long or because there are too many
   // attributes. If this value is 0, then no attributes were dropped.
-  uint32 dropped_attributes_count = 10;
+  uint32 dropped_attributes_count = 9;
 
   // Specifies format of the original payload. Common values are defined in semantic conventions. [required if original_payload is present]
-  string original_payload_format = 11;
+  string original_payload_format = 10;
 
   // Original payload can be stored in this field. This can be useful for users who want to get the original payload.
   // Formats such as JFR are highly extensible and can contain more information than what is defined in this spec.
   // Inclusion of original payload should be configurable by the user. Default behavior should be to not include the original payload.
   // If the original payload is in pprof format, it SHOULD not be included in this field.
   // The field is optional, however if it is present then equivalent converted data should be populated in other fields
   // of this message as far as is practicable.
-  bytes original_payload = 12;
+  bytes original_payload = 11;
 
   // References to attributes in attribute_table. [optional]
   // It is a collection of key/value pairs. Note, global attributes
@@ -286,7 +287,7 @@ message Profile {
   // https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/common/README.md#attribute
   // Attribute keys MUST be unique (it is not allowed to have more than one
   // attribute with the same key).
-  repeated int32 attribute_indices = 13;
+  repeated int32 attribute_indices = 12;
 }
 
 // Represents a mapping between Attribute Keys and Units.
@@ -407,23 +408,20 @@ message ValueType {
 //    values: [2, 2, 3, 3]
 //    timestamps_unix_nano: [1, 2, 3, 4]
 message Sample {
-  // locations_start_index along with locations_length refers to to a slice of locations in Profile.location_indices.
-  int32 locations_start_index = 1;
-  // locations_length along with locations_start_index refers to a slice of locations in Profile.location_indices.
-  // Supersedes location_index.
-  int32 locations_length = 2;
+  // Reference to stack in ProfilesDictionary.stack_table.
+  int32 stack_index = 1;
   // The type and unit of each value is defined by Profile.sample_type.
-  repeated int64 values = 3;
+  repeated int64 values = 2;
   // References to attributes in ProfilesDictionary.attribute_table. [optional]
-  repeated int32 attribute_indices = 4;
+  repeated int32 attribute_indices = 3;
 
   // Reference to link in ProfilesDictionary.link_table. [optional]
   // It can be unset / set to 0 if no link exists, as link_table[0] is always a 'null' default value.
-  int32 link_index = 5;
+  int32 link_index = 4;
 
   // Timestamps associated with Sample represented in nanoseconds. These
   // timestamps should fall within the Profile's time range.
-  repeated uint64 timestamps_unix_nano = 6;
+  repeated uint64 timestamps_unix_nano = 5;
 }
 
 // Describes the mapping of a binary in memory, including its address range,
@@ -448,6 +446,13 @@ message Mapping {
   bool has_inline_frames = 9;
 }
 
+// A Stack represents a stack trace as a list of locations. The first location
+// is the leaf frame.
+message Stack {
+  // References to locations in ProfilesDictionary.location_table.
+  repeated int32 location_indices = 1;
+}
+
 // Describes function and line table debug information.
 message Location {
   // Reference to mapping in ProfilesDictionary.mapping_table.