transactions: Log transaction state when cancelling them

In order to make a transaction's outcome more visible, add a new log
message that is written when cancelling a transaction. Next to the
actual notification that it's got wrapped up, the log message will also
include the number of total nodes registered as part of the transaction,
how many committed and the number of subtransactions created. This
improves visibility and makes it a lot easier to reason about what the
actual result of a transaction is.

2 files changed, 22 insertions, 2 deletions

diff --git a/changelogs/unreleased/pks-tx-log-finished.yml b/changelogs/unreleased/pks-tx-log-finished.yml
new file mode 100644
index 000000000..93f8d4bbf
--- /dev/null
+++ b/changelogs/unreleased/pks-tx-log-finished.yml
@@ -0,0 +1,5 @@
+---
+title: Log transaction state when cancelling them
+merge_request: 2465
+author:
+type: added
diff --git a/internal/praefect/transactions/manager.go b/internal/praefect/transactions/manager.go
index 1afc03588..c3527db16 100644
--- a/internal/praefect/transactions/manager.go
+++ b/internal/praefect/transactions/manager.go
@@ -6,6 +6,7 @@ import (
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
+	"fmt"
 	"math/rand"
 	"sync"
 	"time"
@@ -146,11 +147,11 @@ func (mgr *Manager) RegisterTransaction(ctx context.Context, voters []Voter, thr
 	mgr.counterMetric.WithLabelValues("registered").Add(float64(len(voters)))
 
 	return transaction, func() error {
-		return mgr.cancelTransaction(transaction)
+		return mgr.cancelTransaction(ctx, transaction)
 	}, nil
 }
 
-func (mgr *Manager) cancelTransaction(transaction *Transaction) error {
+func (mgr *Manager) cancelTransaction(ctx context.Context, transaction *Transaction) error {
 	mgr.lock.Lock()
 	defer mgr.lock.Unlock()
 
@@ -159,6 +160,20 @@ func (mgr *Manager) cancelTransaction(transaction *Transaction) error {
 	transaction.cancel()
 	mgr.subtransactionsMetric.Observe(float64(transaction.CountSubtransactions()))
 
+	var committed uint64
+	state := transaction.State()
+	for _, success := range state {
+		if success {
+			committed++
+		}
+	}
+
+	mgr.log(ctx).WithFields(logrus.Fields{
+		"transaction_id":  transaction.ID(),
+		"committed":       fmt.Sprintf("%d/%d", committed, len(state)),
+		"subtransactions": transaction.CountSubtransactions(),
+	}).Info("transaction completed")
+
 	return nil
 }