Deleting predicate using embedded dgraph is slow

[pawanrawal]

There are some tests in client_test/client_test.go which brings up Dgraph in an embedded mode. A couple of them which delete a predicate are slow (> 6 secs) even though there isn't much data to be deleted.

client_test package takes 27 seconds in total though the CPU time is less than 3 secs.

[pawanrawal]

Investigating this. The issue is also reproducible while dgraph is running as a server. To reproduce run this script

#!/bin/bash

date

curl -s localhost:8080/query -XPOST -d '
mutation {
  set {
    <1> <name> "Alice" .
  }
}
' > /dev/null

date

curl -s localhost:8080/query -XPOST -d '
mutation {
  delete {
    * <name> * .
  }
}
' > /dev/null

date