runtime/pprof: memprofile malformed profile: mismatch: sample has

[sealcomeback]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go1.8.1

What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/xiaoju/go"
GORACE=""
GOROOT="/home/xiaoju/push-auto/go1.8.1"
GOTOOLDIR="/home/xiaoju/push-auto/go1.8.1/pkg/tool/linux_amd64"
GCCGO="gccgo"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build603754697=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"
PKG_CONFIG="pkg-config"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"

What did you do?

var memprofile string
flag.StringVar(&memprofile, "memprofile", "memprofile", "write mem profile to this file")
        flag.Parse()
        var memfd *os.File = nil
        var err4 error
        if memprofile != "" {
                memfd, err4 = os.Create(memprofile)
                if err4 != nil {
                        fmt.Printf("create memprofileFile error, %v", err4)
                }
                defer memfd.Close()
        }
        if memfd != nil {
                go memProfileLoop(memfd)
        }
func memProfileLoop(fd *os.File) {
        checkTicker := time.NewTicker(10 * time.Second)
        checkTickerChan := checkTicker.C
        for {
                select {
                case <-checkTickerChan:
                        if fd != nil {
                                //runtime.GC()
                                pprof.WriteHeapProfile(fd)
                                fd.Sync()
                        }
                }
        }
}

What did you see instead?

go tool pprof bin/dispatch memprofile
malformed profile: mismatch: sample has: 4 values vs. 1748 types

[ianlancetaylor]

CC @matloob

[rsc]

Fun bug.

It's not valid to write multiple profiles in sequence to a single file.

Unfortunately:

• profiles are gzipped protocol buffers
• the concatenation of multiple gzipped files is a valid gzipping of the concatenation of their contents
• the concatenation of multiple protocol buffer encodings is a valid encoding of the concatenation of their contents

Because of this, the very concatenated profile is not detected as an invalid profile during decoding. But it appears there are 437 profiles concatenated here, so that the profile header (as concatenated) details 1,748 header fields, while each sample record still only has 4 fields.

It's a very opaque error though. I filed google/pprof#273 upstream with a suggested fix. If they decide to fix it then we'll pick it up in the next sync (likely Go 1.11 at this point).

You can fix this in your program by calling fd.Truncate(0) before writing the profile in the loop.