Update thoughts about BoltDB

store/README.md

@@ -33,3 +33,54 @@ BenchmarkSet_valsize1000-6 	      50	  28066678 ns/op
 BenchmarkSet_valsize10000-6	      50	  28736228 ns/op
 ok  	github.com/dgraph-io/dgraph/store	48.393s
 ```
+
+Also based on dgraph-io/experiments/db:
+
+## BoltDB
+
+Without copying the resulting byte slice from Bolt. **Unsafe**
+```
+$ go test -bench BenchmarkRead .
+testing: warning: no tests to run
+PASS
+BenchmarkReadBolt_1024	  500000	      3858 ns/op
+BenchmarkReadBolt_10KB	  500000	      3738 ns/op
+BenchmarkReadBolt_500KB	 1000000	      3141 ns/op
+BenchmarkReadBolt_1MB	 1000000	      3026 ns/op
+ok  	github.com/dgraph-io/experiments/db	102.513s
+```
+
+Copying the resulting byte slice. **Safe**
+```
+$ go test -bench BenchmarkRead .
+testing: warning: no tests to run
+PASS
+BenchmarkReadBolt_1024	  200000	      6760 ns/op
+BenchmarkReadBolt_10KB	  100000	     21249 ns/op
+BenchmarkReadBolt_500KB	   10000	    214449 ns/op
+BenchmarkReadBolt_1MB	    3000	    350712 ns/op
+ok  	github.com/dgraph-io/experiments/db	80.890s
+```
+
+## RocksDB
+
+```
+$ go test -bench BenchmarkGet .
+PASS
+BenchmarkGet_valsize1024	  300000	      5715 ns/op
+BenchmarkGet_valsize10KB	   50000	     27619 ns/op
+BenchmarkGet_valsize500KB	    2000	    604185 ns/op
+BenchmarkGet_valsize1MB	    2000	   1064685 ns/op
+ok  	github.com/dgraph-io/dgraph/store	55.029s
+```
+
+### Thoughts
+DGraph uses append only commit log to sync new mutations to disk before returning.
+Every time a posting list gets init, it checks for both the stored posting list and
+the mutations committed after the posting list was written. Hence, our access pattern
+from store is largely read-only, with fewer writes. This is true, irrespective of how
+many writes get commited by the end user.
+
+Hence, BoltDB is a better choice. It performs better for reads/seeks, despite DGraph needing
+a value copy. Writes are somewhat slower, but that shouldn't be a problem because of the
+above mentioned reasons.

store/store_test.go

@@ -82,7 +82,6 @@ func benchmarkGet(valSize int, b *testing.B) {
 			return
 		}
 	}
-	b.Logf("Wrote %d keys.", nkeys)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
@@ -98,9 +97,10 @@ func benchmarkGet(valSize int, b *testing.B) {
 	}
 }
 
-func BenchmarkGet_valsize100(b *testing.B)   { benchmarkGet(100, b) }
-func BenchmarkGet_valsize1000(b *testing.B)  { benchmarkGet(1000, b) }
-func BenchmarkGet_valsize10000(b *testing.B) { benchmarkGet(10000, b) }
+func BenchmarkGet_valsize1024(b *testing.B)  { benchmarkGet(1024, b) }
+func BenchmarkGet_valsize10KB(b *testing.B)  { benchmarkGet(10240, b) }
+func BenchmarkGet_valsize500KB(b *testing.B) { benchmarkGet(1<<19, b) }
+func BenchmarkGet_valsize1MB(b *testing.B)   { benchmarkGet(1<<20, b) }
 
 func benchmarkSet(valSize int, b *testing.B) {
 	path, err := ioutil.TempDir("", "storetest_")
@@ -125,6 +125,7 @@ func benchmarkSet(valSize int, b *testing.B) {
 	}
 }
 
-func BenchmarkSet_valsize100(b *testing.B)   { benchmarkSet(100, b) }
-func BenchmarkSet_valsize1000(b *testing.B)  { benchmarkSet(1000, b) }
-func BenchmarkSet_valsize10000(b *testing.B) { benchmarkSet(10000, b) }
+func BenchmarkSet_valsize1024(b *testing.B)  { benchmarkSet(1024, b) }
+func BenchmarkSet_valsize10KB(b *testing.B)  { benchmarkSet(10240, b) }
+func BenchmarkSet_valsize500KB(b *testing.B) { benchmarkSet(1<<19, b) }
+func BenchmarkSet_valsize1MB(b *testing.B)   { benchmarkSet(1<<20, b) }