A KeyValue stream's max messages per subject isn't being respected after updating the stream's max messages per subject to be smaller than before

[anthonyjacques20]

What version were you using?

2.9.21

What environment was the server running in?

Mac M1

Is this defect reproducible?

Yes, this is reproducible. Run a nats server with jetstream enabled and then run the following test:

package history_test

import (
	"encoding/json"
	"strconv"
	"testing"

	"github.com/nats-io/nats.go"
	"github.com/stretchr/testify/require"
)

func TestHistory(t *testing.T) {
	// Start server with `nats-server --js` to make sure jetstream is turned on
	nc, err := nats.Connect(nats.DefaultURL)
	require.Nil(t, err)

	// Create jetstream and KeyValue
	js, err := nc.JetStream()
	require.Nil(t, err)
	bucketName := "HistoryTest"
	kv, err := js.CreateKeyValue(&nats.KeyValueConfig{
		Bucket:      bucketName,
		Description: "Test for number of historical values",
		History:     10,
	})
	require.Nil(t, err)
	key := "mykey"

	// Write to the same key 50 times
	for j := 0; j < 50; j++ {
		value := strconv.Itoa(j)
		marshalledBytes, err := json.Marshal(value)
		require.Nil(t, err)
		_, err = kv.Put(key, marshalledBytes)
		require.Nil(t, err)
	}
	// Verify we have the correct amount of history
	info, err := js.StreamInfo("KV_" + bucketName)
	require.Nil(t, err)
	histories, err := kv.History(key)
	require.Nil(t, err)
	require.Len(t, histories, int(info.Config.MaxMsgsPerSubject))

	// Update the stream to store half the amount of history as before
	newConfig := info.Config
	newConfig.MaxMsgsPerSubject = newConfig.MaxMsgsPerSubject / 2
	info, err = js.UpdateStream(&newConfig)
	require.Nil(t, err)

	// Write 50 more values
	for j := 0; j < 50; j++ {
		value := strconv.Itoa(50 + j)
		marshalledBytes, err := json.Marshal(value)
		require.Nil(t, err)
		_, err = kv.Put(key, marshalledBytes)
		require.Nil(t, err)
	}
	// Verify that the history has the updated number of max messages per subject
	histories, err = kv.History(key)
	require.Nil(t, err)
	require.Len(t, histories, int(info.Config.MaxMsgsPerSubject)) // We fail here...
}

Given the capability you are leveraging, describe your expectation?

My expectation is that after updating the Max Messages Per Subject for the Stream, the corresponding KeyValue should contain the updated amount of history

Given the expectation, what is the defect you are observing?

After updating the stream associated with the KV, it is storing more history than it should be storing.

[ripienaar]

Tried to reproduce this:

$ nats kv add X --replicas 3 --history 10

$ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
do
nats kv put X y $i
done

$ nats kv history X y
#...shows 10 history

$ nats s edit KV_X --max-msgs-per-subject 5 -f
$ nats kv history X y
#...shows 5 history

$ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
do
nats kv put X y $i
done

$ nats kv history X y
#...shows 20 history

So can confirm this also affects 2.10

[derekcollison]

Server issue, will move.