SG Accelerator documentation

I am running example couchbase-sg-accel by

./bin/sync_gateway ./examples/basic_sg_accel_config.json

but I got nothing but:

2016-07-11T17:05:02.588+08:00 Enabling logging: [HTTP+]
2016-07-11T17:05:02.589+08:00 PANIC: SG is running in normal mode but there are databases configured as index writers -- rest.ValidateConfigOrPanic() at config.go:688
panic: SG is running in normal mode but there are databases configured as index writers

goroutine 1 [running]:
github.com/couchbase/sync_gateway/base.LogPanic(0x4ac1540, 0x50, 0x0, 0x0, 0x0)
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/base/logging.go:229 +0x107
github.com/couchbase/sync_gateway/rest.ValidateConfigOrPanic(0x4002000)
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/rest/config.go:688 +0xae
github.com/couchbase/sync_gateway/rest.ServerMain(0xc800000000)
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/rest/config.go:704 +0x2a
main.main()
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/main.go:34 +0x133

goroutine 17 [syscall, locked to thread]:
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1721 +0x1

goroutine 19 [syscall]:
os/signal.loop()
	/usr/local/go/src/os/signal/signal_unix.go:22 +0x18
created by os/signal.init.1
	/usr/local/go/src/os/signal/signal_unix.go:28 +0x37

goroutine 23 [select, locked to thread]:
runtime.gopark(0x4bc36b8, 0xc82002a728, 0x4986bb8, 0x6, 0x18, 0x2)
	/usr/local/go/src/runtime/proc.go:185 +0x163
runtime.selectgoImpl(0xc82002a728, 0x0, 0x18)
	/usr/local/go/src/runtime/select.go:392 +0xa64
runtime.selectgo(0xc82002a728)
	/usr/local/go/src/runtime/select.go:212 +0x12
runtime.ensureSigM.func1()
	/usr/local/go/src/runtime/signal1_unix.go:227 +0x323
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1721 +0x1

goroutine 24 [chan receive]:
main.main.func1(0xc820156900)
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/main.go:28 +0x51
created by main.main
	/Users/jenkins/jenkins/workspace/sync-gateway-unix-builds/release/1.2.1/enterprise/app-under-test/sync_gateway/src/github.com/couchbase/sync_gateway/main.go:32 +0x12a

It really confuse me :
Q1: What is couchbase-sg-accel? ( What is the difference between Couchbase-sg and couchbase-sg-accel)
Q2: How should I use couchbase-sg-accel?