don't pre allocate mutation map

[poonai]

Signed-off-by: balaji jinnah rbalajis25@gmail.com

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This change is 

[martinmr]

Not sure if the change would have a lot of impact but it should be fine as long as you fix the breaking tests. The stacktrace below seems directly related to the change:

------- Stdout: -------
=== RUN   TestExportRdf
--- FAIL: TestExportRdf (0.01s)
panic: assignment to entry in nil map [recovered]
	panic: assignment to entry in nil map

goroutine 46 [running]:
testing.tRunner.func1(0xc0002a0900)
	/usr/local/go/src/testing/testing.go:830 +0x392
panic(0x14fed00, 0x17c14d0)
	/usr/local/go/src/runtime/panic.go:522 +0x1b5
github.com/dgraph-io/dgraph/posting.(*List).updateMutationLayer(0xc000093800, 0xc0000ef860)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/posting/list.go:323 +0x232
github.com/dgraph-io/dgraph/posting.(*List).addMutationInternal(0xc000093800, 0x17fa340, 0xc0000c8010, 0xc0002aafc0, 0xc0000ef680, 0xc0004bebf8, 0xc0004bebf8)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/posting/list.go:444 +0xb1
github.com/dgraph-io/dgraph/posting.(*Txn).addMutationHelper(0xc0002aafc0, 0x17fa340, 0xc0000c8010, 0xc000093800, 0x0, 0xc0000ef680, 0x0, 0x0, 0x0, 0x8db500, ...)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/posting/index.go:361 +0x205
github.com/dgraph-io/dgraph/posting.(*List).AddMutationWithIndex(0xc000093800, 0x17fa340, 0xc0000c8010, 0xc0000ef680, 0xc0002aafc0, 0x13, 0x0)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/posting/index.go:394 +0x11e
github.com/dgraph-io/dgraph/worker.commitTransaction(0xc0002a0900, 0xc0000ef680, 0xc000093800)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/worker/predicate_test.go:71 +0x102
github.com/dgraph-io/dgraph/worker.addEdge(...)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/worker/worker_test.go:50
github.com/dgraph-io/dgraph/worker.populateGraphExport(0xc0002a0900)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/worker/export_test.go:98 +0x4d0
github.com/dgraph-io/dgraph/worker.initTestExport(0xc0002a0900, 0x1650e53, 0x14)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/worker/export_test.go:134 +0x94c
github.com/dgraph-io/dgraph/worker.TestExportRdf(0xc0002a0900)
	/home/pawan0201/go/src/github.com/dgraph-io/dgraph/worker/export_test.go:184 +0x58
testing.tRunner(0xc0002a0900, 0x1696008)
	/usr/local/go/src/testing/testing.go:865 +0xc0
created by testing.(*T).Run
	/usr/local/go/src/testing/testing.go:916 +0x35a
exit status 2
FAIL	github.com/dgraph-io/dgraph/worker	0.098s

Reviewed 1 of 1 files at r1.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @manishrjain)

[manishrjain]

Looks good from my side. Got one comment. Please address @martinmr and get his approval.

Reviewed 2 of 2 files at r2.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @balajijinnah)

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posting/list.go, line 82 at r2 (raw file):

// initialize map if it's nil. caller has to take care of
// lock.
func (l *List) initializeMutationMap() {

I doubt there's a need for this func. Maybe remove this func and just inline the code.

[poonai]

Reviewable status: 0 of 3 files reviewed, 1 unresolved discussion (waiting on @manishrjain)

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posting/list.go, line 82 at r2 (raw file):

Previously, manishrjain (Manish R Jain) wrote…

I doubt there's a need for this func. Maybe remove this func and just inline the code.

Done.

[manishrjain]

Reviewed 3 of 3 files at r3.
Reviewable status: all files reviewed, 1 unresolved discussion (waiting on @manishrjain)