panic in dgraph/query/query.go:492

[relunctance]

If you suspect this could be a bug, follow the template.

• What version of Dgraph are you using?

Dgraph version   : v1.0.11-rc3-4-g701e18d0
Commit SHA-1     : 701e18d0
Commit timestamp : 2018-11-21 23:56:55 -0800
Branch           : master

• Have you tried reproducing the issue with latest release?
  yes

• What is the hardware spec (RAM, OS)?

CentOS release 6.2 (Final)
Linux 2.6.32-220.7.1.el6.x86_64 #1 SMP Wed Mar 7 00:52:02 GMT 2012 x86_64 x86_64 x86_64 GNU/Linux 
MemTotal:       65910848 kB
MemFree:        24531660 kB
Buffers:          441096 kB

• Steps to reproduce the issue (command/config used to run Dgraph).
  Data size and schema:

md5 <md5>: string @index(exact) @upsert . 7212931
pmd5 <pmd5>: uid @count @reverse . 6715929
xid <xid>: string @index(hash) . 7212931

url: http://127.0.0.1:8080/query?debug=true

{
  node(func: eq(md5, "72460aa5d07e44a639880f0aa129f3db")) {
    uid
    expand(_all_)  {
      expand(_all_)
    }
  }
}

• Expected behaviour and actual result.

 492             if pc.Params.Facet != nil && len(pc.facetsMatrix[idx].FacetsList) > 0 {
 493                 // in case of Value we have only one Facets
 494                 for _, f := range pc.facetsMatrix[idx].FacetsList[0].Facets {
 495                     dst.AddValue(facetName(fieldName, f), facets.ValFor(f))
 496                 }
 497             }

2018/12/06 14:17:58 http: panic serving 10.18.32.38:58464: runtime error: index out of range
goroutine 2160787 [running]:
net/http.(*conn).serve.func1(0xc4e6529360)
    /home/gaoqilin/usr/local/go/src/net/http/server.go:1697 +0xd0
panic(0x148be40, 0x1db4190)
    /home/gaoqilin/usr/local/go/src/runtime/panic.go:491 +0x283
github.com/dgraph-io/dgraph/query.(*SubGraph).preTraverse(0xc42041a580, 0xc749d9, 0x1de7960, 0xc5667b9ec0, 0xc5667b9ec0, 0x0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/query/query.go:492 +0x1800
github.com/dgraph-io/dgraph/query.(*SubGraph).preTraverse(0xc4203322c0, 0x6b4500, 0x1de7960, 0xc4e66ce780, 0x11e3fdb, 0xc4345caac0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/query/query.go:442 +0x404
github.com/dgraph-io/dgraph/query.processNodeUids(0xc43b9095b8, 0xc4203322c0, 0xc6154c6150, 0x0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/query/outputnode.go:452 +0x1d1
github.com/dgraph-io/dgraph/query.(*SubGraph).toFastJSON(0xc43b909678, 0xc6154c6150, 0x0, 0x0, 0x0, 0x0, 0x0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/query/outputnode.go:500 +0x135
github.com/dgraph-io/dgraph/query.ToJson(0xc6154c6150, 0xc442cc0c80, 0x1, 0x1, 0x1, 0x1, 0x0, 0x0, 0x0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/query/outputnode.go:53 +0x1e1
github.com/dgraph-io/dgraph/edgraph.(*Server).Query(0xc420321b98, 0x1de30c0, 0xc6154c6120, 0xc626ee94a0, 0xc69c46a120, 0x0, 0x0)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/edgraph/server.go:499 +0x75f
github.com/dgraph-io/dgraph/dgraph/cmd/alpha.queryHandler(0x1de2000, 0xc42e17c000, 0xc550006000)
    /home/gaoqilin/gopath/src/github.com/dgraph-io/dgraph/dgraph/cmd/alpha/http.go:107 +0x354
net/http.HandlerFunc.ServeHTTP(0x160bc78, 0x1de2000, 0xc42e17c000, 0xc550006000)
    /home/gaoqilin/usr/local/go/src/net/http/server.go:1918 +0x44
net/http.(*ServeMux).ServeHTTP(0x1e816a0, 0x1de2000, 0xc42e17c000, 0xc550006000)
    /home/gaoqilin/usr/local/go/src/net/http/server.go:2254 +0x130
net/http.serverHandler.ServeHTTP(0xc420402270, 0x1de2000, 0xc42e17c000, 0xc550006000)
    /home/gaoqilin/usr/local/go/src/net/http/server.go:2619 +0xb4
net/http.(*conn).serve(0xc4e6529360, 0x1de3000, 0xc4f1f37080)
    /home/gaoqilin/usr/local/go/src/net/http/server.go:1801 +0x71d
created by net/http.(*Server).Serve
    /home/gaoqilin/usr/local/go/src/net/http/server.go:2720 +0x288

[danielmai]

This is fixed in the latest v1.0.11-rc4 with 290028d