"concurrent map read and map write" panics during workloads with JOIN queries

statement = SELECT u.email AS email, COUNT(t.title) FROM `bucket-2` t INNER JOIN `bucket-3` c ON META(c).id IN t.categories LEFT OUTER JOIN `bucket-1` u ON t.owner = META(u).id WHERE t.capped = $1 AND c.name = $2 GROUP BY u.email;

goroutine 472914126 [running]:

runtime.throw(0xfb7d7a, 0x21)

        /home/couchbase/.cbdepscache/exploded/x86_64/go-1.8.5/go/src/runtime/panic.go:596 +0x95 fp=0xc429e32878 sp=0xc429e32858

runtime.mapaccess2_faststr(0xe2eb80, 0xc436d75ec0, 0xc444779290, 0x6, 0xde8720, 0xc429e32970)

        /home/couchbase/.cbdepscache/exploded/x86_64/go-1.8.5/go/src/runtime/hashmap_fast.go:326 +0x50a fp=0xc429e328d8 sp=0xc429e32878

github.com/couchbase/query/value.(*parsedValue).Field(0xc43cd9a190, 0xc444779290, 0x6, 0x0, 0x0, 0x0)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/value/parsed.go:180 +0x737 fp=0xc429e329f0 sp=0xc429e328d8

github.com/couchbase/query/value.(*annotatedValue).Field(0xc435787ec0, 0xc444779290, 0x6, 0x18bcac0, 0xc435787ec0, 0xc429e32a01)

        <autogenerated>:85 +0x60 fp=0xc429e32a30 sp=0xc429e329f0

github.com/couchbase/query/expression.(*Field).Apply(0xc441737c70, 0x189bb00, 0xc4510fd760, 0x18bcac0, 0xc435787ec0, 0x18bd960, 0xc4447792f0, 0x0, 0x0, 0x0, ...)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/nav_field.go:138 +0xd0 fp=0xc429e32b00 sp=0xc429e32a30

github.com/couchbase/query/expression.(*BinaryFunctionBase).BinaryEval(0xc441737c70, 0x18912c0, 0xc441737c70, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0xc423e6c480, 0x18, 0x18, ...)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/function.go:385 +0x18c fp=0xc429e32ba0 sp=0xc429e32b00

github.com/couchbase/query/expression.(*Field).Evaluate(0xc441737c70, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0xc429e32cd0, 0x412c02, 0xc42c48ff00, 0x80)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/nav_field.go:52 +0x70 fp=0xc429e32c08 sp=0xc429e32ba0

github.com/couchbase/query/expression.(*BinaryFunctionBase).BinaryEval(0xc441737cc0, 0x1891200, 0xc441737cc0, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0x80, 0xdf8480, 0x1, ...)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/function.go:379 +0xc8 fp=0xc429e32ca8 sp=0xc429e32c08

github.com/couchbase/query/expression.(*Eq).Evaluate(0xc441737cc0, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0x5afdbdef, 0x1ed82695, 0xc429e32d68, 0x4896b2)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/comp_eq.go:48 +0x70 fp=0xc429e32d10 sp=0xc429e32ca8

github.com/couchbase/query/expression.(*FunctionBase).Eval(0xc441737ea0, 0x1890080, 0xc441737ea0, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0x0, 0x0, 0x0, ...)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/function.go:142 +0x123 fp=0xc429e32da8 sp=0xc429e32d10

github.com/couchbase/query/expression.(*And).Evaluate(0xc441737ea0, 0x18bcac0, 0xc4332e82a0, 0x189bb00, 0xc4510fd760, 0xc4299e9180, 0x18c22a0, 0xc4215d70e0, 0x18d7280)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/expression/logic_and.go:43 +0x70 fp=0xc429e32e10 sp=0xc429e32da8

github.com/couchbase/query/execution.(*Filter).processItem(0xc4299e9180, 0x18d7280, 0xc4332e82a0, 0xc4510fd760, 0x1)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/execution/filter.go:50 +0xa3 fp=0xc429e32e78 sp=0xc429e32e10

github.com/couchbase/query/execution.(*base).runConsumer.func1()

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/execution/base.go:547 +0x25d fp=0xc429e32f00 sp=0xc429e32e78

github.com/couchbase/query/util.(*Once).Do(0xc4299e9278, 0xc42603c738)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/util/sync.go:51 +0x68 fp=0xc429e32f28 sp=0xc429e32f00

github.com/couchbase/query/execution.(*base).runConsumer(0xc4299e9180, 0x189dc80, 0xc4299e9180, 0xc4510fd760, 0x0, 0x0)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/execution/base.go:552 +0xaf fp=0xc429e32f80 sp=0xc429e32f28

github.com/couchbase/query/execution.(*Filter).RunOnce(0xc4299e9180, 0xc4510fd760, 0x0, 0x0)

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/execution/filter.go:46 +0x5c fp=0xc429e32fc0 sp=0xc429e32f80

runtime.goexit()

        /home/couchbase/.cbdepscache/exploded/x86_64/go-1.8.5/go/src/runtime/asm_amd64.s:2197 +0x1 fp=0xc429e32fc8 sp=0xc429e32fc0

created by github.com/couchbase/query/execution.(*base).runConsumer.func1

        /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/query/execution/base.go:537 +0x2f6