internal/trace/v2: don't enforce batch order on Ms

Currently the trace parser enforces that the timestamps for a series of
a batches on the same M come in order. We cannot actually assume this in
general because we don't trust timestamps. The source of truth on the
batch order is the order in which they were emitted. If that's wrong, it
should quickly become evident in the trace.

For #60773.
For #64061.

Change-Id: I7d5a407c9568dd1ce0b79d51b2b538ed6072b26d
Reviewed-on: https://go-review.googlesource.com/c/go/+/541695
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Knyszek <mknyszek@google.com>

diff --git a/src/internal/trace/v2/generation.go b/src/internal/trace/v2/generation.go
index b4305157939c75117ce5acff9bd90694cebd5555..4cdf76e21c06f95463fbff4d819a4f837f23ceac 100644 (file)
--- a/src/internal/trace/v2/generation.go
+++ b/src/internal/trace/v2/generation.go
@@ -95,15 +95,11 @@ func readGeneration(r *bufio.Reader, spill *spilledBatch) (*generation, *spilled
        if g.freq == 0 {
                return nil, nil, fmt.Errorf("no frequency event found")
        }
-       for _, batches := range g.batches {
-               sorted := slices.IsSortedFunc(batches, func(a, b batch) int {
-                       return cmp.Compare(a.time, b.time)
-               })
-               if !sorted {
-                       // TODO(mknyszek): Consider just sorting here.
-                       return nil, nil, fmt.Errorf("per-M streams are out-of-order")
-               }
-       }
+       // N.B. Trust that the batch order is correct. We can't validate the batch order
+       // by timestamp because the timestamps could just be plain wrong. The source of
+       // truth is the order things appear in the trace and the partial order sequence
+       // numbers on certain events. If it turns out the batch order is actually incorrect
+       // we'll very likely fail to advance a partial order from the frontier.
 
        // Compactify stacks and strings for better lookup performance later.
        g.stacks.compactify()