GODT-2085: Ensure minimum sync worker count

Make sure that we are at least using 16 workers for sync, otherwise
multiply the current sync worker count by 2.

Finally, this patch also logs the duration of the time it takes to
transfer all the messages from the server.

internal/user/sync.go

@@ -20,6 +20,7 @@ package user
 import (
 	"context"
 	"fmt"
+	"runtime"
 	"strings"
 	"time"
 
@@ -32,6 +33,7 @@ import (
 	"github.com/bradenaw/juniper/parallel"
 	"github.com/bradenaw/juniper/xslices"
 	"github.com/google/uuid"
+	"github.com/sirupsen/logrus"
 	"gitlab.protontech.ch/go/liteapi"
 	"golang.org/x/exp/maps"
 )
@@ -197,6 +199,13 @@ func syncMessages( //nolint:funlen
 		return fmt.Errorf("failed to get message IDs to sync: %w", err)
 	}
 
+	syncStartTime := time.Now()
+	defer func() {
+		syncFinishTime := time.Now()
+		logrus.Infof("Message sync completed in %v", syncFinishTime.Sub(syncStartTime))
+	}()
+	logrus.Infof("Starting message sync with syncWorkers=%v (numCpu=%v) for %v messages", syncWorkers, runtime.NumCPU(), len(messageIDs))
+
 	// Create the flushers, one per update channel.
 	flushers := make(map[string]*flusher, len(updateCh))
 
@@ -223,7 +232,7 @@ func syncMessages( //nolint:funlen
 	// Allow up to 4 batched wait requests.
 	flushUpdateCh := make(chan flushUpdate, 4)
 
-	errorCh := make(chan error, syncWorkers*2)
+	errorCh := make(chan error, syncWorkers)
 
 	// Goroutine in charge of downloading and building messages in maxBatchSize batches.
 	go func() {
@@ -236,7 +245,7 @@ func syncMessages( //nolint:funlen
 				return
 			}
 
-			result, err := parallel.MapContext(ctx, int(float32(syncWorkers)*1.5), batch, func(ctx context.Context, id string) (*buildRes, error) {
+			result, err := parallel.MapContext(ctx, syncWorkers, batch, func(ctx context.Context, id string) (*buildRes, error) {
 				msg, err := client.GetFullMessage(ctx, id)
 				if err != nil {
 					return nil, err