TxnLockNotFound

[gfreezy]

#[tokio::main]
async fn main() -> Result<()> {
    let txn_client = TransactionClient::new(vec!["127.0.0.1:2379"]).await?;
    let mut txn = txn_client.begin_optimistic().await.unwrap();
    let key = "aa".to_owned();
    txn.insert(key.clone(), "value".to_owned()).await.unwrap();
    txn.delete(key.clone()).await.unwrap();
    txn.commit().await.unwrap();
    Ok(())
}

The above code raise the following error:

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: StringError("KeyError { locked: None, retryable: \"Error(Txn(Error(Mvcc(Error(TxnLockNotFound { start_ts: TimeStamp(427084398190919681), commit_ts: TimeStamp(427084398190919682), key: [97, 97] })))))\", abort: \"\", conflict: None, already_exist: None, deadlock: None, commit_ts_expired: None, txn_not_found: None, commit_ts_too_large: None }")', src/main.rs:347:24
stack backtrace:
   0: rust_begin_unwind
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/std/src/panicking.rs:517:5
   1: core::panicking::panic_fmt
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/core/src/panicking.rs:93:14
   2: core::result::unwrap_failed
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/core/src/result.rs:1617:5
   3: core::result::Result<T,E>::unwrap
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/core/src/result.rs:1299:23
   4: scratch::main::{{closure}}
             at ./src/main.rs:347:5
   5: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/core/src/future/mod.rs:80:19
   6: tokio::park::thread::CachedParkThread::block_on::{{closure}}
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/park/thread.rs:263:54
   7: tokio::coop::with_budget::{{closure}}
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/coop.rs:106:9
   8: std::thread::local::LocalKey<T>::try_with
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/std/src/thread/local.rs:399:16
   9: std::thread::local::LocalKey<T>::with
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/std/src/thread/local.rs:375:9
  10: tokio::coop::with_budget
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/coop.rs:99:5
  11: tokio::coop::budget
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/coop.rs:76:5
  12: tokio::park::thread::CachedParkThread::block_on
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/park/thread.rs:263:31
  13: tokio::runtime::enter::Enter::block_on
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/runtime/enter.rs:151:13
  14: tokio::runtime::thread_pool::ThreadPool::block_on
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/runtime/thread_pool/mod.rs:71:9
  15: tokio::runtime::Runtime::block_on
             at /Users/feichao/.cargo/registry/src/github.com-1ecc6299db9ec823/tokio-1.10.0/src/runtime/mod.rs:452:43
  16: scratch::main
             at ./src/main.rs:348:5
  17: core::ops::function::FnOnce::call_once
             at /rustc/ae90dcf0207c57c3034f00b07048d63f8b2363c8/library/core/src/ops/function.rs:227:5

Tikv setup:

[ekexium]

~Which version are you using?~

Thanks for your feedback! Confirmed it's a bug. TiKV doesn't actually write mutations whose op are CheckNotExists. client-rust mistakenly treats it the same way as other operations.

[gfreezy]

Is it a TiKV bug or client-rust's ?

[ekexium]

It's cilent-rust's

[gfreezy]

I'd like to try fixing the bug. Any Docs or guide how to do it?

[ekexium]

CheckNotExists is checked in the prewrite phase and should not appear in the commit phase. So I think there are basically two things to do:

1. When we set the primary key of a transaction, the corresponding operation must not be CheckNotExists.
2. We should filter out mutations with CheckNotExists in the commit phase.

[gfreezy]

What does primary key means in a tikv transaction?

[ekexium]

The primary key can be viewed as a representative of the transaction. Each transaction that needs to write some key-values must have a primary key.

In client-rust, the primary key of a transaction is set at https://github.com/tikv/client-rust/blob/eb1d2da05cc857818e078bc3d91ce50343031642/src/transaction/buffer.rs#L12

There is a difference in how primary keys are set between TiDB(client-go) and client-rust. cilent-go doesn't set the primary key until committing. client-rust, in the current implementation, can set the primary key when locking keys. I think we may need to consider whether there is a better way to do this.

[gfreezy]

Should we change the way how primary key is set to be the same as go?

[ekexium]

Should we change the way how primary key is set to be the same as go?

That's one way to fix the issue. But it may introduce other subtleties. For example, pessimistic lock requests require a primary key, even when the transaction isn't ready to commit. Maybe we can temporarily set the PK as the key that needs to be locked? We must carefully reason its correctness.

I don't have a simple solution for now. @andylokandy do you have any good ideas?

[andylokandy]

@ekexium I have a question about the case this PR is going to resolve: what should the PK be if a transaction's mutations contain only one CheckNotExist? e.g.: begin, insert('k1'), delete('k1'), commit