Nil value returned due to movekey version mismatch

[simon-xe-wang]

What version of Go are you using (go version)?

$ go version

What version of Badger are you using?

v1.5.5

Does this issue reproduce with the latest master?

What are the hardware specifications of the machine (RAM, OS, Disk)?

What did you do?

1. keep writing keys
   each round writes 1.5 million keys (768 bytes for key and 1024 for value) and repeatedly update those keys. all in same goroutine

2. vlog gc every 5 minutes in another goroutine and read keys to verify.
   I can upload test program if needed.

What did you expect to see?

What did you see instead?

after a while, in my case from 3 hours to 15 hours, I got nil value returned. which is DL issue.

[simon-xe-wang]

After tracing in code. the reason it returns nil value is that the original key has new version v2 in lsm tree. move key only has older version v1, v2 is lost.

see iterator.go: yieldItemValue
if vs.Version != item.Version() {
return nil, nil, nil
}

[manishrjain]

@ibrahim can you look into this?

[jarifibrahim]

@SimonXW Can you share the test program?

[simon-xe-wang]

main.txt

[simon-xe-wang]

Just uploaded test code. rename it to .go.

[jarifibrahim]

@SimonXW I ran your program twice. The first time it kept running for 10 hours and then again for 3 hours. I didn't see any nil values. Can you try running the program again and confirm the issue?

[simon-xe-wang]

I ran it 3/4 times and got nil value every time. but from 3 hours to 15 hours. Also which version are you running on? I ran it on 1.5.4 + the patch for #907.

You may have to run it longer.

[jarifibrahim]

I tried it on v1.5.5 (as mentioned in the issue). I'll try it once again with 1.5.4.

[markadev]

Hi, I'm a colleague of @SimonXW. I think that we were hitting a bug in 1.5 that was fixed with this commit: af99e5f

After upgrading to 1.6.0, I no longer see the nil value problem with this test program any more.

[jarifibrahim]

Thanks @markadev. Since this issue is no longer reproducible on 1.6.0 I'm going to close this issue.