Panic: Index out of range error when merging profiles

[aleks-p]

Encountered index out of range errors in the read path (ingesters):

pyroscope/pkg/pprof/merge.go

Lines 257 to 261 in 4fdd876

	func RewriteMappings(p *profilev1.Profile, n []uint32) {
	for _, loc := range p.Location {
	loc.MappingId = uint64(n[loc.MappingId-1]) + 1
	}
	}

called from:

pyroscope/pkg/pprof/merge.go

Lines 66 to 68 in 4fdd876

	m.tmp = slices.GrowLen(m.tmp, len(p.Mapping))
	m.mappingTable.Index(m.tmp, p.Mapping)
	RewriteMappings(p, m.tmp)

golang.org/x/sync@v0.5.0/errgroup/errgroup.go:72 +0x96
created by golang.org/x/sync/errgroup.(*Group).Go in goroutine 93207350
golang.org/x/sync@v0.5.0/errgroup/errgroup.go:75 +0x56
golang.org/x/sync/errgroup.(*Group).Go.func1()
github.com/grafana/pyroscope/pkg/phlaredb/symdb/resolver.go:263 +0x138
github.com/grafana/pyroscope/pkg/phlaredb/symdb.(*Resolver).withSymbols.func1()
github.com/grafana/pyroscope/pkg/phlaredb/symdb/resolver.go:248 +0x178
github.com/grafana/pyroscope/pkg/phlaredb/symdb.(*Resolver).Pprof.func1(0x2258460?, {{0xc18379d420, 0x1, 0x1}, {0xc18379d428, 0x1, 0x1}, {0x0, 0x0, 0x0}})
github.com/grafana/pyroscope/pkg/pprof/merge.go:26
github.com/grafana/pyroscope/pkg/pprof.(*ProfileMerge).Merge(...)
github.com/grafana/pyroscope/pkg/pprof/merge.go:68 +0x62d
github.com/grafana/pyroscope/pkg/pprof.(*ProfileMerge).merge(0xc02ecaa7e0, 0xc0aee65350, 0x1?)
github.com/grafana/pyroscope/pkg/pprof/merge.go:259
github.com/grafana/pyroscope/pkg/pprof.RewriteMappings(...)
goroutine 93207317 [running]:

panic: runtime error: index out of range [0] with length 0

At a glance it looks like we are unable to merge profiles that have no mappings.

[kolesnikovae]

Thanks for creating the issue. This is interesting: we assume that at least one mapping must be present. I'll take a look into this.