Update badger to v20.0.7-rc1

Also, disable conflict detection in badger to save memory.

```
0dfb8b4 Changelog for v20.07.0 (hypermodeinc/badger#1411)
03ba278 Add missing changelog for v2.0.3 (hypermodeinc/badger#1410)
6001230 Revert "Compress/Encrypt Blocks in the background (hypermodeinc/badger#1227)" (hypermodeinc/badger#1409)
800305e Revert "Buffer pool for decompression
(hypermodeinc/badger#1308)"
(hypermodeinc/badger#1408)
63d9309 Revert "fix: Fix race condition in block.incRef
(hypermodeinc/badger#1337)"
(hypermodeinc/badger#1407)
e0d058c Revert "add assert to check integer overflow for table size (hypermodeinc/badger#1402)" (hypermodeinc/badger#1406)
d981f47 return error if the vlog writes exceeds more that 4GB.
(hypermodeinc/badger#1400)
7f4e4b5 add assert to check integer overflow for table size
(hypermodeinc/badger#1402)
8e896a7 Add a contribution guide
(hypermodeinc/badger#1379)
b79aeef Avoid panic on multiple closer.Signal calls
(hypermodeinc/badger#1401)
717b89c Enable cross-compiled 32bit tests on TravisCI
(hypermodeinc/badger#1392)
09dfa66 Update ristretto to commit f66de99
(hypermodeinc/badger#1391)
509de73 Update head while replaying value log
(hypermodeinc/badger#1372)
e013bfd Rework DB.DropPrefix (hypermodeinc/badger#1381)
3042e37 pre allocate cache key for the block cache and the bloom filter cache (hypermodeinc/badger#1371)
675efcd Increase default valueThreshold from 32B to 1KB
(hypermodeinc/badger#1346)
158d927 Remove second initialization of writech in Open
(hypermodeinc/badger#1382)
d37ce36 Tests: Use t.Parallel in TestIteratePrefix tests
(hypermodeinc/badger#1377)
3f4761d Force KeepL0InMemory to be true when InMemory is true
(hypermodeinc/badger#1375)
dd332b0 Avoid panic in filltables()
(hypermodeinc/badger#1365)
c45d966 Fix assert in background compression and encryption.
(hypermodeinc/badger#1366)
```

go.mod

@@ -16,9 +16,9 @@ require (
 	github.com/blevesearch/segment v0.0.0-20160915185041-762005e7a34f // indirect
 	github.com/blevesearch/snowballstem v0.0.0-20180110192139-26b06a2c243d // indirect
 	github.com/codahale/hdrhistogram v0.0.0-20161010025455-3a0bb77429bd
-	github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200609141616-14386ac9b764
+	github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200711090415-0dfb8b45d4a4
 	github.com/dgraph-io/dgo/v2 v2.1.1-0.20191127085444-c7a02678e8a6
-	github.com/dgraph-io/ristretto v0.0.2-0.20200115201040-8f368f2f2ab3
+	github.com/dgraph-io/ristretto v0.0.3-0.20200630154024-f66de99634de
 	github.com/dgrijalva/jwt-go v3.2.0+incompatible
 	github.com/dgryski/go-farm v0.0.0-20200201041132-a6ae2369ad13
 	github.com/dgryski/go-groupvarint v0.0.0-20190318181831-5ce5df8ca4e1

go.sum

@@ -62,12 +62,12 @@ github.com/d4l3k/messagediff v1.2.1/go.mod h1:Oozbb1TVXFac9FtSIxHBMnBCq2qeH/2KkE
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200609141616-14386ac9b764 h1:cWmYs+E7F/w4KWIkVrV3VLUJkqolRa7y5G2LLMPQVQs=
-github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200609141616-14386ac9b764/go.mod h1:3KY8+bsP8wI0OEnQJAKpd4wIJW/Mm32yw2j/9FUVnIM=
+github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200711090415-0dfb8b45d4a4 h1:M85aROJxDOXmp8mZQN6x04EraKDGOF2RL3ox/6LZdjo=
+github.com/dgraph-io/badger/v2 v2.0.1-rc1.0.20200711090415-0dfb8b45d4a4/go.mod h1:26P/7fbL4kUZVEVKLAKXkBXKOydDmM2p1e+NhhnBCAE=
 github.com/dgraph-io/dgo/v2 v2.1.1-0.20191127085444-c7a02678e8a6 h1:5leDFqGys055YO3TbghBhk/QdRPEwyLPdgsSJfiR20I=
 github.com/dgraph-io/dgo/v2 v2.1.1-0.20191127085444-c7a02678e8a6/go.mod h1:LJCkLxm5fUMcU+yb8gHFjHt7ChgNuz3YnQQ6MQkmscI=
-github.com/dgraph-io/ristretto v0.0.2-0.20200115201040-8f368f2f2ab3 h1:MQLRM35Pp0yAyBYksjbj1nZI/w6eyRY/mWoM1sFf4kU=
-github.com/dgraph-io/ristretto v0.0.2-0.20200115201040-8f368f2f2ab3/go.mod h1:KPxhHT9ZxKefz+PCeOGsrHpl1qZ7i70dGTu2u+Ahh6E=
+github.com/dgraph-io/ristretto v0.0.3-0.20200630154024-f66de99634de h1:t0UHb5vdojIDUqktM6+xJAfScFBsVpXZmqC9dsgJmeA=
+github.com/dgraph-io/ristretto v0.0.3-0.20200630154024-f66de99634de/go.mod h1:KPxhHT9ZxKefz+PCeOGsrHpl1qZ7i70dGTu2u+Ahh6E=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible h1:7qlOGliEKZXTDg6OTjfoBKDXWrumCAMpl/TFQ4/5kLM=
 github.com/dgrijalva/jwt-go v3.2.0+incompatible/go.mod h1:E3ru+11k8xSBh+hMPgOLZmtrrCbhqsmaPHjLKYnJCaQ=
 github.com/dgryski/go-farm v0.0.0-20190423205320-6a90982ecee2/go.mod h1:SqUrOPUnsFjfmXRMNPybcSiG0BgUW2AuFH8PAnS2iTw=

worker/server_state.go

@@ -173,6 +173,9 @@ func (s *ServerState) initStorage() {
 		glog.Infof("Opening postings BadgerDB with options: %+v\n", opt)
 		opt.EncryptionKey = key
 
+		// Disable conflict detection in badger since dgraph performs it's own conflict detection.
+		opt.DetectConflicts = false
+
 		s.Pstore, err = badger.OpenManaged(opt)
 		x.Checkf(err, "Error while creating badger KV posting store")