diff --git a/execution/exchange/coalesce.go b/execution/exchange/coalesce.go
index d7bdc818..3d5b64de 100644
--- a/execution/exchange/coalesce.go
+++ b/execution/exchange/coalesce.go
@@ -18,16 +18,20 @@ import (
 	"github.com/prometheus/prometheus/model/labels"
 )
 
-type errorChan chan error
-
-func (c errorChan) getError() error {
-	for err := range c {
-		if err != nil {
-			return err
+func drainErrChan(ch chan error) error {
+	for {
+		select {
+		case err := <-ch:
+			if err != nil {
+				for range len(ch) {
+					<-ch
+				}
+				return err
+			}
+		default:
+			return nil
 		}
 	}
-
-	return nil
 }
 
 // coalesce is a model.VectorOperator that merges input vectors from multiple downstream operators
@@ -40,19 +44,16 @@ type coalesce struct {
 
 	wg        sync.WaitGroup
 	operators []model.VectorOperator
-	batchSize int64
 
 	// inVectors is an internal per-step cache for references to input vectors.
 	inVectors [][]model.StepVector
-	// sampleOffsets holds per-operator offsets needed to map an input sample ID to an output sample ID.
+	// sampleOffsets maps an input sample ID to an output sample ID.
 	sampleOffsets []uint64
-	// seriesCounts holds the number of series per operator for pre-allocation.
-	seriesCounts []int
-	// tempBufs are reusable buffers for reading from operators
-	tempBufs [][]model.StepVector
+	tempBufs      [][]model.StepVector
+	errChan       chan error
 }
 
-func NewCoalesce(opts *query.Options, batchSize int64, operators ...model.VectorOperator) model.VectorOperator {
+func NewCoalesce(opts *query.Options, operators ...model.VectorOperator) model.VectorOperator {
 	if len(operators) == 1 {
 		return operators[0]
 	}
@@ -60,7 +61,7 @@ func NewCoalesce(opts *query.Options, batchSize int64, operators ...model.Vector
 		sampleOffsets: make([]uint64, len(operators)),
 		operators:     operators,
 		inVectors:     make([][]model.StepVector, len(operators)),
-		batchSize:     batchSize,
+		errChan:       make(chan error, len(operators)),
 	}
 
 	return telemetry.NewOperator(telemetry.NewTelemetry(oper, opts), oper)
@@ -96,8 +97,6 @@ func (c *coalesce) Next(ctx context.Context, buf []model.StepVector) (int, error
 		return 0, err
 	}
 
-	// Allocate temporary buffers on first use.
-	// Inner slices will be lazily pre-allocated by child operators when they append data.
 	if c.tempBufs == nil {
 		c.tempBufs = make([][]model.StepVector, len(c.operators))
 		for i := range c.tempBufs {
@@ -105,19 +104,8 @@ func (c *coalesce) Next(ctx context.Context, buf []model.StepVector) (int, error
 		}
 	}
 
-	var mu sync.Mutex
-	var minTs int64 = math.MaxInt64
-	var errChan = make(errorChan, len(c.operators))
-	vectorCounts := make([]int, len(c.operators))
-
 	for idx, o := range c.operators {
-		// We already have a batch from the previous iteration.
 		if c.inVectors[idx] != nil {
-			mu.Lock()
-			if len(c.inVectors[idx]) > 0 {
-				minTs = min(minTs, c.inVectors[idx][0].T)
-			}
-			mu.Unlock()
 			continue
 		}
 
@@ -126,18 +114,16 @@ func (c *coalesce) Next(ctx context.Context, buf []model.StepVector) (int, error
 			defer c.wg.Done()
 			defer func() {
 				if r := recover(); r != nil {
-					errChan <- errors.Newf("unexpected panic: %v", r)
+					c.errChan <- errors.Newf("unexpected panic: %v", r)
 				}
 			}()
 
 			n, err := o.Next(ctx, c.tempBufs[opIdx])
 			if err != nil {
-				errChan <- err
+				c.errChan <- err
 				return
 			}
-			vectorCounts[opIdx] = n
 
-			// Map input IDs to output IDs.
 			for i := range n {
 				vector := &c.tempBufs[opIdx][i]
 				for j := range vector.SampleIDs {
@@ -150,35 +136,34 @@ func (c *coalesce) Next(ctx context.Context, buf []model.StepVector) (int, error
 
 			if n > 0 {
 				c.inVectors[opIdx] = c.tempBufs[opIdx][:n]
-				mu.Lock()
-				minTs = min(minTs, c.tempBufs[opIdx][0].T)
-				mu.Unlock()
 			} else {
 				c.inVectors[opIdx] = nil
 			}
 		}(idx, o)
 	}
 	c.wg.Wait()
-	close(errChan)
 
-	if err := errChan.getError(); err != nil {
+	if err := drainErrChan(c.errChan); err != nil {
 		return 0, err
 	}
 
-	// Count vectors with minTs and prepare output
+	var minTs int64 = math.MaxInt64
+	for _, vectors := range c.inVectors {
+		if len(vectors) > 0 {
+			minTs = min(minTs, vectors[0].T)
+		}
+	}
+
 	n := 0
 	for opIdx, vectors := range c.inVectors {
 		if len(vectors) == 0 || vectors[0].T != minTs {
 			continue
 		}
 
-		// Initialize output vectors if needed
 		if n == 0 {
 			maxSteps := min(len(vectors), len(buf))
 			for i := range maxSteps {
 				buf[i].Reset(vectors[i].T)
-				// Ensure sufficient capacity for float samples.
-				// Histogram slices will grow on demand since most queries don't use them.
 				totalSamples := 0
 				totalHistograms := 0
 				for _, v := range c.inVectors {
@@ -199,13 +184,11 @@ func (c *coalesce) Next(ctx context.Context, buf []model.StepVector) (int, error
 			n = maxSteps
 		}
 
-		// Append samples from this operator
 		for i := 0; i < n && i < len(vectors); i++ {
 			buf[i].AppendSamples(vectors[i].SampleIDs, vectors[i].Samples)
 			buf[i].AppendHistograms(vectors[i].HistogramIDs, vectors[i].Histograms)
 		}
 
-		// Keep remaining vectors for next iteration
 		if n < len(vectors) {
 			c.inVectors[opIdx] = vectors[n:]
 		} else {
@@ -220,19 +203,18 @@ func (c *coalesce) loadSeries(ctx context.Context) error {
 	var wg sync.WaitGroup
 	var numSeries uint64
 	allSeries := make([][]labels.Labels, len(c.operators))
-	errChan := make(errorChan, len(c.operators))
 	for i := range c.operators {
 		wg.Add(1)
 		go func(i int) {
 			defer wg.Done()
 			defer func() {
 				if r := recover(); r != nil {
-					errChan <- errors.Newf("unexpected panic: %v", r)
+					c.errChan <- errors.Newf("unexpected panic: %v", r)
 				}
 			}()
 			series, err := c.operators[i].Series(ctx)
 			if err != nil {
-				errChan <- err
+				c.errChan <- err
 				return
 			}
 
@@ -241,22 +223,16 @@ func (c *coalesce) loadSeries(ctx context.Context) error {
 		}(i)
 	}
 	wg.Wait()
-	close(errChan)
-	if err := errChan.getError(); err != nil {
+	if err := drainErrChan(c.errChan); err != nil {
 		return err
 	}
 
 	c.sampleOffsets = make([]uint64, len(c.operators))
-	c.seriesCounts = make([]int, len(c.operators))
 	c.series = make([]labels.Labels, 0, numSeries)
 	for i, series := range allSeries {
 		c.sampleOffsets[i] = uint64(len(c.series))
-		c.seriesCounts[i] = len(series)
 		c.series = append(c.series, series...)
 	}
 
-	if c.batchSize == 0 || c.batchSize > int64(len(c.series)) {
-		c.batchSize = int64(len(c.series))
-	}
 	return nil
 }
diff --git a/execution/execution.go b/execution/execution.go
index 6d20339b..21c76097 100644
--- a/execution/execution.go
+++ b/execution/execution.go
@@ -372,7 +372,7 @@ func newDeduplication(ctx context.Context, e logicalplan.Deduplicate, scanners s
 		}
 		operators[i] = operator
 	}
-	coalesce := exchange.NewCoalesce(opts, 0, operators...)
+	coalesce := exchange.NewCoalesce(opts, operators...)
 	dedup := exchange.NewDedupOperator(coalesce, opts)
 	return exchange.NewConcurrent(dedup, 2, opts), nil
 }
diff --git a/storage/prometheus/scanners.go b/storage/prometheus/scanners.go
index bac38431..94bdd3e7 100644
--- a/storage/prometheus/scanners.go
+++ b/storage/prometheus/scanners.go
@@ -79,7 +79,7 @@ func (p Scanners) NewVectorSelector(
 		operators = append(operators, operator)
 	}
 
-	return exchange.NewCoalesce(opts, logicalNode.BatchSize*int64(opts.DecodingConcurrency), operators...), nil
+	return exchange.NewCoalesce(opts, operators...), nil
 }
 
 func (p Scanners) NewMatrixSelector(
@@ -156,7 +156,7 @@ func (p Scanners) NewMatrixSelector(
 		operators = append(operators, exchange.NewConcurrent(operator, 2, opts))
 	}
 
-	return exchange.NewCoalesce(opts, vs.BatchSize*int64(opts.DecodingConcurrency), operators...), nil
+	return exchange.NewCoalesce(opts, operators...), nil
 }
 
 type histogramStatsSelector struct {