garage/script/jepsen.garage/README.md

# jepsen.garage

Jepsen checking of Garage consistency properties.

## Usage

Requirements:

- vagrant
- VirtualBox, configured so that nodes can take an IP in a private network `192.168.56.0/24`
- a user that can create VirtualBox VMs
- leiningen
- gnuplot

Set up VMs:

```
vagrant up
```

Run tests (this one should fail):

```
lein run test --nodes-file nodes.vagrant --time-limit 64 --concurrency 50 --rate 50 --workload reg
```

These ones are working:

```
lein run test --nodes-file nodes.vagrant --time-limit 64 --rate 50  --concurrency 50 --workload set1
lein run test --nodes-file nodes.vagrant --time-limit 64 --rate 50  --concurrency 50 --workload set2
```

## Results

### Register linear, without timestamp patch

Command: `lein run test --nodes-file nodes.vagrant --time-limit 60 --rate 20  --concurrency 20 --workload reg1 --ops-per-key 100`

Results: fails with a simple clock-scramble nemesis.

Explanation: without the timestamp patch, nodes will create objects using their
local clock only as a timestamp, so the ordering will be all over the place if
clocks are scrambled.

### Register linear, with timestamp patch

Command: `lein run test --nodes-file nodes.vagrant --time-limit 60 --rate 20  --concurrency 20 --workload reg1 --ops-per-key 100 -I`

Results:

- No failure with clock-scramble nemesis
- Fails with clock-scramble nemesis + partition nemesis

Explanation: S3 objects are not meant to behave like linearizable registers. TODO explain using a counter-example

### Read-after-write CRDT register model, without timestamp patch

Command: `lein run test --nodes-file nodes.vagrant --time-limit 60 --rate 100  --concurrency 100 --workload reg2 --ops-per-key 100`

Results: fails with a simple clock-scramble nemesis.

Explanation: old values are not overwritten correctly when their timestamps are in the future.

### Read-after-write CRDT register model, with timestamp patch

Command: `lein run test --nodes-file nodes.vagrant --time-limit 60 --rate 100  --concurrency 100 --workload reg2 --ops-per-key 100 -I`

Results:

- Failures with clock-scramble nemesis + partition nemesis ???? TODO INVESTIGATE
  -> the issue seems to be only after DeleteObject (deletions are not always taken into account),
     the issue does not appear if we are using only PutObject with an actual object content
- TODO: layout reconfiguration nemesis


### Set, basic test (write some items, then read)

Command: `lein run test --nodes-file nodes.vagrant --time-limit 60 --rate 100  --concurrency 100 --workload set1 --ops-per-key 100`

Results:

- For now, no failures with clock-scramble nemesis + partition nemesis
- TODO: layout reconfiguration nemesis

### Set, continuous test (interspersed reads and writes)

TODO


## Investigating (and fixing) errors

### Segfaults

They are due to the download being interrupted in the middle (^C during first launch on clean VMs), the `garage` binary is truncated.
Add `:force?` to the `cached-wget!` call in `daemon.clj` to re-download the binary.

### In `jepsen.garage`: prefix wierdness

In `store/garage set1/20231019T163358.615+0200`:

```
INFO [2023-10-19 16:35:20,977] clojure-agent-send-off-pool-207 - jepsen.garage.set list results for prefix set20/ : (set13/0 set13/1 set13/10 set13/11 set13/12 set13/13 set13/14 set13/15 set13/16 set13/17 set13/18 set13/19 set13/2 set13/20 set13/21 set13/22 set13/23 set13/24 set13/25 set13/26 set13/27 set13/28 set13/29 set13/3 set13/30 set13/31 set13/32 set13/33 set13/34 set13/35 set13/36 set13/37 set13/38 set13/39 set13/4 set13/40 set13/41 set13/42 set13/43 set13/44 set13/45 set13/46 set13/47 set13/48 set13/49 set13/5 set13/50 set13/51 set13/52 set13/53 set13/54 set13/55 set13/56 set13/57 set13/58 set13/59 set13/6 set13/60 set13/61 set13/62 set13/63 set13/64 set13/65 set13/66 set13/67 set13/68 set13/69 set13/7 set13/70 set13/71 set13/72 set13/73 set13/74 set13/75 set13/76 set13/77 set13/78 set13/79 set13/8 set13/80 set13/81 set13/82 set13/83 set13/84 set13/85 set13/86 set13/87 set13/88 set13/89 set13/9 set13/90 set13/91 set13/92 set13/93 set13/94 set13/95 set13/96 set13/97 set13/98 set13/99)  (node: http://192.168.56.25:3900 )
```

After inspecting, the actual S3 call made was with prefix "set13/", so at least this is not an error in Garage itself but in the jepsen code.

Finally found out that this was due to closures not correctly capturing their context in the list function in s3api.clj (wtf clojure?)
Not sure exactly where it came from but it seems to have been fixed by making list-inner a separate function and not a sub-function,
and passing all values that were previously in the context (creds and prefix) as additional arguments.

### `reg2` test inconsistency, even with timestamp fix

The reg2 test is our custom checker for CRDT read-after-write on individual object keys, acting as registers which can be updated.
The test fails without the timestamp fix, which is expected as the clock scrambler will prevent nodes from having a correct ordering of objects.

With the timestamp fix, the happenned-before relationship should at least be respected, meaning that when a PutObject call starts
after another PutObject call has ended, the second call should overwrite the value of the first call, and that value should not be
readable by future GetObject calls.
However, we observed inconsistencies even with the timestamp fix.

The inconsistencies seemed to always happenned after writing a nil value, which translates to a DeleteObject call
instead of a PutObject. By removing the possibility of writing nil values, therefore only doing
PutObject calls, the issue disappears. There is therefore an issue to fix in DeleteObject.



## License

Copyright © 2023 Alex Auvolat

This program and the accompanying materials are made available under the
terms of the GNU Affero General Public License v3.0.