1 # Perfetto trace format 2 3 *** note 4 **This doc is WIP**, stay tuned. 5 <!-- TODO(primiano): write trace format doc. --> 6 *** 7 8 A Perfetto trace is guaranteed to be a a linear sequence of `TracePacket(s)` 9 (see [trace_packet.proto](/protos/perfetto/trace/trace_packet.proto)). 10 11 As a key part of the Perfetto design, the tracing service is agnostic of the 12 content of TracePacket, modulo the few fields defined in 13 [trusted_packet.proto](/protos/perfetto/trace/trusted_packet.proto) that are 14 produced by the service itself. 15 16 Each data source can extend the trace with their app-specific protobuf schema. 17 *** aside 18 TODO(primiano): we should reserve an extension range and figure out / comment a 19 hash to assign sub-message IDs, even without checking them into 20 trace_packet.proto. 21 *** 22 23 24 **Linearity guarantees** 25 The tracing service guarantees that all `TracePacket(s)` written by a given 26 `TraceWriter` are seen in-order, without gaps or duplicates. If, for any reason, 27 a `TraceWriter` sequence becomes invalid, no more packets are returned to the 28 Consumer (or written into the trace file). 29 30 However, `TracePacket(s)` written by different `TraceWriter` (hence even 31 different producers) can be seen in no particular order. 32 The consumer can re-establish a total order, if interested, using the packet 33 timestamps (after having synchronized the different clocks onto a global clock). 34
