Disappearing edges

[emadsamir]

If you suspect this could be a bug, follow the template.

• What version of Dgraph are you using? 1.0.3

• Have you tried reproducing the issue with latest release? yes

• What is the hardware spec (RAM, OS)? 8GB, LINUX

• Steps to reproduce the issue (command/config used to run Dgraph).
  quads := fmt.Sprintf(<%s> * * ., node_id)
  if parent_id != nil {
  quads += fmt.Sprintf("\n<%s> <%s> <%s> .", parent_id, edge, node_id)
  }
  _, err := txn.Mutate(bgctx, &api.Mutation{
  CommitNow: true,
  DelNquads: byte(quads),
  })

• Expected behaviour and actual result.
  after that, parent_id, will not show any edge references to other nodes until you create a new one, which tells me that they are not deleted but only sort of hidden.

[pawanrawal]

This is not a complete example. It would be really helpful if your example is a program/test which shows all the queries and mutations. @emadsamir can you please modify it to have this information?

[emadsamir]

this is description i put on the forum:
I am just wondering if you are aware that when you delete a predicate on a parent node, that causes all the other predicates to not show until a new one is created.
for example given:
<1> p <2>
<1> p <3>
<1> p <4>

delete{
<1> p <3> .
}

then!
<1> p <2>
<1> p <4>
no longer recongized

until you create a new
<1> p <5>

[emadsamir]

it might be helpful to state that I am querying via Ratel something like such:
{nodes(func: has(p)){
uid
expand(all){uid}
}}

before delete all 3 edges will show, after, no result
after a new edge created then 3 edges including newly created will show.

To be honest, I am surprised that no one has reported this yet, but maybe because I am really focused on testing creation and deletion of edges that became so apparent to me.

[pawanrawal]

I could not reproduce this from the information that you have given. Is it possible for you to share a complete reproducible example in Go or even a shell script using cURL statements?

[emadsamir]

it's part of a big project. I will work on isolating go code for you.

[emadsamir]

The below reproduces the problem:

mu := &api.Mutation{
		CommitNow: true,
		SetNquads: []byte(`
<0x1> <type> "x" .
<0x2> <type> "y" .
<0x3> <type> "y" .
<0x4> <type> "y" .
<0x1> <to> <0x2> .
<0x1> <to> <0x3> .
<0x1> <to> <0x4> .
`),
	}

NOW query via Ratel:

{nodes(func: has(to)){
  uid
  expand(_all_){uid}
}}

you will get 4 nodes and 3 edges

Then run this

mu := &api.Mutation{
		CommitNow: true,DelNquads: []byte(\`
<0x4> * * .
<0x1> <to> <0x4> .
\`),
	}

NOW query via Ratel: all edges are gone!

[pawanrawal]

Thanks, @emadsamir. That was helpful in reproducing the issue. I have a fix for this in PR #2195. Its a bug with the expand(_all_) query. Other queries which directly request for to edges would work just fine. For e.g.

{
  nodes(func: has(to)){
    uid
    to {
      uid
    }
  }
}

Since most people don't use expand(_all_) in production, no one noticed it.

[emadsamir]

thanks @pawanrawal for getting on top of this & pointing out a workaround for the time being.
I was, maybe still am concerned about the data integrity of current release when you start manipulating data and schema. for example, I had a major issue when I toggled a predicate "reverse" property on and off, I had to resort to deleting all data and starting over. I do understand that might be a separate issue, but it was worth mentioning.

[pawanrawal]

Can you share the issue about toggling the reverse property and why you had to delete all the data and start over again?

[emadsamir]

server_1  | Got schema: [predicate:"roles" value_type:UID directive:REVERSE ]
zero_1    | 2018/03/03 07:39:33 oracle.go:84: purging below ts:20136, len(o.commits):2, len(o.aborts):0
server_1  | 2018/03/02 00:12:22 mutation.go:187: Done schema update predicate:"roles" value_type:UID directive:REVERSE 
server_1  | 2018/03/02 00:13:11 groups.go:296: Asking if I can serve tablet for: _share_hash_
server_1  | Got schema: [predicate:"roles" value_type:UID ]

after that I couldn't use Ratel after that, not sure if it's related to the below

server_1  | 2018/03/03 07:47:22 groups.go:454: Unable to sync memberships. Error: rpc error: code = DeadlineExceeded desc = context deadline exceeded
server_1  | 2018/03/03 07:47:22 groups.go:670: Error in oracle delta stream. Error: rpc error: code = Unknown desc = Node is no longer leader.