[TINKERPOP-2767] Repeat Out Times traversal hangs indefinitely on first execution

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 3.5.3
• Fix Version/s: 3.7.0, 3.6.3, 3.5.6
• Component/s: server
• Environment: Windows 10
• Assignee: Yang Xia
• Reporter: Simon Zhao
• Created: 24/Jun/22 00:59
• Updated: 01/May/23 16:41
• Resolved: 01/May/23 16:41

Description

Originally encountered when fixing TINKERPOP-2754

 

The following traversal in JS seems to cause hanging the first time you run it on a newly launched gremlin-server (3.5.3) via docker

 
await g.V('1').repeat(_.out()).times(1500).next();
 
The same hanging occurs in gremlin-go. 
 

_, err = g.With("evaluationTimeout", 1000).V("1").Repeat(gremlingo.T__.Out()).Times(int32(1500)).Next() 

 

The timeout is optional, but indicates that something is going wrong since it is not returning. Interestingly enough, if the timeout is very low, then it won't hang because it will say the timeout was exceeded. This indicates that if the traversal is completed within the timeout, it's just not returning for some reason on the first call.

 

If you were to write a script and invoke this snippet of code, it will hang. If you forcefully terminate the script and rerun it, then it doesn't hang.

 

main.go

package main

import (
   gremlingo "github.com/apache/tinkerpop/gremlin-go/v3/driver"
   "log"
)

func main() {
   driver, err := gremlingo.NewDriverRemoteConnection("ws://localhost:45940/gremlin")
   if err != nil {
      log.Print("Err creating DRC")
      return
   }
   defer driver.Close()

   log.Println("Start")
   g := gremlingo.Traversal_().WithRemote(driver)
   LABEL := "test"
   _, err = g.V().HasLabel(LABEL).Drop().Next()
   _, err = g.AddV(LABEL).Property(gremlingo.T.Id, "1").Next()
   _, err = g.AddV(LABEL).Property(gremlingo.T.Id, "2").Next()
   _, err = g.AddE(LABEL).From(gremlingo.T__.V("1")).To(gremlingo.T__.V("2")).Property(gremlingo.T.Id, "e1").Next()
   _, err = g.AddE(LABEL).From(gremlingo.T__.V("2")).To(gremlingo.T__.V("1")).Property(gremlingo.T.Id, "e2").Next()
   if err != nil {
      log.Println("Error during setup")
      return
   }
   log.Println("Start the problematic traversal")
   _, err = g.With("evaluationTimeout", 1000).V("1").Repeat(gremlingo.T__.Out()).Times(int32(1500)).Next()
   if err != nil {
      log.Println("Error with the problematic traversal, but we didn't hang")
      return
   }
   log.Println("End")
} 

Issue Links

• relates to: TINKERPOP-2343 Allow for some form of max unroll length for RepeatUnrollStrategy