@@ -112,11 +112,17 @@ ForgeNoTxsDelay Duration `validate:"-"`
 	// MustForgeAtSlotDeadline enables the coordinator to forge slots if
 	// the empty slots reach the slot deadline.
 	MustForgeAtSlotDeadline bool
-	// IgnoreSlotCommitment IgnoreSlotCommitment disables forcing the
-	// coordinator to forge a slot immediately when the slot is not
-	// committed. If set to false, the coordinator will immediately forge
-	// a batch at the beginning of a slot if it's the slot winner.
+	// IgnoreSlotCommitment disables forcing the coordinator to forge a
+	// slot immediately when the slot is not committed. If set to false,
+	// the coordinator will immediately forge a batch at the beginning of a
+	// slot if it's the slot winner.
 	IgnoreSlotCommitment bool
+	// ForgeOncePerSlotIfTxs will make the coordinator forge at most one
+	// batch per slot, only if there are included txs in that batch, or
+	// pending l1UserTxs in the smart contract.  Setting this parameter
+	// overrides `ForgeDelay`, `ForgeNoTxsDelay`, `MustForgeAtSlotDeadline`
+	// and `IgnoreSlotCommitment`.
+	ForgeOncePerSlotIfTxs bool
 	// SyncRetryInterval is the waiting interval between calls to the main
 	// handler of a synced block after an error
 	SyncRetryInterval Duration `validate:"required"`

@@ -85,7 +85,7 @@ Proof                 *prover.Proof
 	PublicInputs          []*big.Int
 	L1Batch               bool
 	VerifierIdx           uint8
-	L1UserTxsExtra        []common.L1Tx
+	L1UserTxs             []common.L1Tx
 	L1CoordTxs            []common.L1Tx
 	L1CoordinatorTxsAuths [][]byte
 	L2Txs                 []common.L2Tx

@@ -24,10 +24,8 @@ "github.com/hermeznetwork/tracerr"
 )
 
 var (
-	errLastL1BatchNotSynced  = fmt.Errorf("last L1Batch not synced yet")
-	errForgeNoTxsBeforeDelay = fmt.Errorf(
-		"no txs to forge and we haven't reached the forge no txs delay")
-	errForgeBeforeDelay = fmt.Errorf("we haven't reached the forge delay")
+	errLastL1BatchNotSynced = fmt.Errorf("last L1Batch not synced yet")
+	errSkipBatchByPolicy    = fmt.Errorf("skip batch by policy")
 )
 
 const (
@@ -92,6 +90,12 @@ // slot immediately when the slot is not committed. If set to false,
 	// the coordinator will immediately forge a batch at the beginning of
 	// a slot if it's the slot winner.
 	IgnoreSlotCommitment bool
+	// ForgeOncePerSlotIfTxs will make the coordinator forge at most one
+	// batch per slot, only if there are included txs in that batch, or
+	// pending l1UserTxs in the smart contract.  Setting this parameter
+	// overrides `ForgeDelay`, `ForgeNoTxsDelay`, `MustForgeAtSlotDeadline`
+	// and `IgnoreSlotCommitment`.
+	ForgeOncePerSlotIfTxs bool
 	// SyncRetryInterval is the waiting interval between calls to the main
 	// handler of a synced block after an error
 	SyncRetryInterval time.Duration

@@ -224,8 +224,9 @@ }()
 
 	// 2. Forge the batch internally (make a selection of txs and prepare
 	// all the smart contract arguments)
+	var skipReason *string
 	p.mutexL2DBUpdateDelete.Lock()
-	batchInfo, err = p.forgeBatch(batchNum)
+	batchInfo, skipReason, err = p.forgeBatch(batchNum)
 	p.mutexL2DBUpdateDelete.Unlock()
 	if ctx.Err() != nil {
 		return nil, ctx.Err()
@@ -234,13 +235,13 @@ if tracerr.Unwrap(err) == errLastL1BatchNotSynced {
 			log.Warnw("forgeBatch: scheduled L1Batch too early", "err", err,
 				"lastForgeL1TxsNum", p.state.lastForgeL1TxsNum,
 				"syncLastForgeL1TxsNum", p.stats.Sync.LastForgeL1TxsNum)
-		} else if tracerr.Unwrap(err) == errForgeNoTxsBeforeDelay ||
-			tracerr.Unwrap(err) == errForgeBeforeDelay {
-			// no log
 		} else {
 			log.Errorw("forgeBatch", "err", err)
 		}
 		return nil, tracerr.Wrap(err)
+	} else if skipReason != nil {
+		log.Debugw("skipping batch", "batch", batchNum, "reason", *skipReason)
+		return nil, tracerr.Wrap(errSkipBatchByPolicy)
 	}
 
 	// 3. Send the ZKInputs to the proof server
@@ -295,8 +296,7 @@ batchInfo, err := p.handleForgeBatch(p.ctx, batchNum)
 				if p.ctx.Err() != nil {
 					continue
 				} else if tracerr.Unwrap(err) == errLastL1BatchNotSynced ||
-					tracerr.Unwrap(err) == errForgeNoTxsBeforeDelay ||
-					tracerr.Unwrap(err) == errForgeBeforeDelay {
+					tracerr.Unwrap(err) == errSkipBatchByPolicy {
 					continue
 				} else if err != nil {
 					p.setErrAtBatchNum(batchNum)
@@ -389,25 +389,109 @@ }
 	return nil
 }
 
-// check if we reach the ForgeDelay or not before batch forging
-func (p *Pipeline) preForgeBatchCheck(slotCommitted bool, now time.Time) error {
-	if slotCommitted && now.Sub(p.lastForgeTime) < p.cfg.ForgeDelay {
-		return errForgeBeforeDelay
+// slotCommitted returns true if the current slot has already been committed
+func (p *Pipeline) slotCommitted() bool {
+	// Synchronizer has synchronized a batch in the current slot (setting
+	// CurrentSlot.ForgerCommitment) or the pipeline has already
+	// internally-forged a batch in the current slot
+	return p.stats.Sync.Auction.CurrentSlot.ForgerCommitment ||
+		p.stats.Sync.Auction.CurrentSlot.SlotNum == p.state.lastSlotForged
+}
+
+// forgePolicySkipPreSelection is called before doing a tx selection in a batch to
+// determine by policy if we should forge the batch or not.  Returns true and
+// the reason when the forging of the batch must be skipped.
+func (p *Pipeline) forgePolicySkipPreSelection(now time.Time) (bool, string) {
+	// Check if the slot is not yet fulfilled
+	slotCommitted := p.slotCommitted()
+	if p.cfg.ForgeOncePerSlotIfTxs {
+		if slotCommitted {
+			return true, "cfg.ForgeOncePerSlotIfTxs = true and slot already committed"
+		}
+		return false, ""
 	}
-	return nil
+	// Determine if we must commit the slot
+	if !p.cfg.IgnoreSlotCommitment && !slotCommitted {
+		return false, ""
+	}
+
+	// If we haven't reached the ForgeDelay, skip forging the batch
+	if now.Sub(p.lastForgeTime) < p.cfg.ForgeDelay {
+		return true, "we haven't reached the forge delay"
+	}
+	return false, ""
+}
+
+// forgePolicySkipPostSelection is called after doing a tx selection in a batch to
+// determine by policy if we should forge the batch or not.  Returns true and
+// the reason when the forging of the batch must be skipped.
+func (p *Pipeline) forgePolicySkipPostSelection(now time.Time, l1UserTxsExtra, l1CoordTxs []common.L1Tx,
+	poolL2Txs []common.PoolL2Tx, batchInfo *BatchInfo) (bool, string, error) {
+	// Check if the slot is not yet fulfilled
+	slotCommitted := p.slotCommitted()
+
+	pendingTxs := true
+	if len(l1UserTxsExtra) == 0 && len(l1CoordTxs) == 0 && len(poolL2Txs) == 0 {
+		if batchInfo.L1Batch {
+			// Query the number of unforged L1UserTxs
+			// (either in a open queue or in a frozen
+			// not-yet-forged queue).
+			count, err := p.historyDB.GetUnforgedL1UserTxsCount()
+			if err != nil {
+				return false, "", err
+			}
+			// If there are future L1UserTxs, we forge a
+			// batch to advance the queues to be able to
+			// forge the L1UserTxs in the future.
+			// Otherwise, skip.
+			if count == 0 {
+				pendingTxs = false
+			}
+		} else {
+			pendingTxs = false
+		}
+	}
+
+	if p.cfg.ForgeOncePerSlotIfTxs {
+		if slotCommitted {
+			return true, "cfg.ForgeOncePerSlotIfTxs = true and slot already committed",
+				nil
+		}
+		if pendingTxs {
+			return false, "", nil
+		}
+		return true, "cfg.ForgeOncePerSlotIfTxs = true and no pending txs",
+			nil
+	}
+
+	// Determine if we must commit the slot
+	if !p.cfg.IgnoreSlotCommitment && !slotCommitted {
+		return false, "", nil
+	}
+
+	// check if there is no txs to forge, no l1UserTxs in the open queue to
+	// freeze and we haven't reached the ForgeNoTxsDelay
+	if now.Sub(p.lastForgeTime) < p.cfg.ForgeNoTxsDelay {
+		if !pendingTxs {
+			return true, "no txs to forge and we haven't reached the forge no txs delay",
+				nil
+		}
+	}
+	return false, "", nil
 }
 
 // forgeBatch forges the batchNum batch.
-func (p *Pipeline) forgeBatch(batchNum common.BatchNum) (batchInfo *BatchInfo, err error) {
+func (p *Pipeline) forgeBatch(batchNum common.BatchNum) (batchInfo *BatchInfo,
+	skipReason *string, err error) {
 	// remove transactions from the pool that have been there for too long
 	_, err = p.purger.InvalidateMaybe(p.l2DB, p.txSelector.LocalAccountsDB(),
 		p.stats.Sync.LastBlock.Num, int64(batchNum))
 	if err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 	_, err = p.purger.PurgeMaybe(p.l2DB, p.stats.Sync.LastBlock.Num, int64(batchNum))
 	if err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 	// Structure to accumulate data and metadata of the batch
 	now := time.Now()
@@ -417,53 +501,48 @@ batchInfo.Debug.StartBlockNum = p.stats.Eth.LastBlock.Num + 1
 
 	var poolL2Txs []common.PoolL2Tx
 	var discardedL2Txs []common.PoolL2Tx
-	var l1UserTxsExtra, l1CoordTxs []common.L1Tx
+	var l1UserTxs, l1CoordTxs []common.L1Tx
 	var auths [][]byte
 	var coordIdxs []common.Idx
 
-	// Check if the slot is not yet fulfilled
-	slotCommitted := p.cfg.IgnoreSlotCommitment
-	if p.stats.Sync.Auction.CurrentSlot.ForgerCommitment ||
-		p.stats.Sync.Auction.CurrentSlot.SlotNum == p.state.lastSlotForged {
-		slotCommitted = true
-	}
-
-	// If we haven't reached the ForgeDelay, skip forging the batch
-	if err = p.preForgeBatchCheck(slotCommitted, now); err != nil {
-		return nil, tracerr.Wrap(err)
+	if skip, reason := p.forgePolicySkipPreSelection(now); skip {
+		return nil, &reason, nil
 	}
 
 	// 1. Decide if we forge L2Tx or L1+L2Tx
 	if p.shouldL1L2Batch(batchInfo) {
 		batchInfo.L1Batch = true
 		if p.state.lastForgeL1TxsNum != p.stats.Sync.LastForgeL1TxsNum {
-			return nil, tracerr.Wrap(errLastL1BatchNotSynced)
+			return nil, nil, tracerr.Wrap(errLastL1BatchNotSynced)
 		}
 		// 2a: L1+L2 txs
-		l1UserTxs, err := p.historyDB.GetUnforgedL1UserTxs(p.state.lastForgeL1TxsNum + 1)
+		_l1UserTxs, err := p.historyDB.GetUnforgedL1UserTxs(p.state.lastForgeL1TxsNum + 1)
 		if err != nil {
-			return nil, tracerr.Wrap(err)
+			return nil, nil, tracerr.Wrap(err)
 		}
-		coordIdxs, auths, l1UserTxsExtra, l1CoordTxs, poolL2Txs, discardedL2Txs, err =
-			p.txSelector.GetL1L2TxSelection(p.cfg.TxProcessorConfig, l1UserTxs)
+		coordIdxs, auths, l1UserTxs, l1CoordTxs, poolL2Txs, discardedL2Txs, err =
+			p.txSelector.GetL1L2TxSelection(p.cfg.TxProcessorConfig, _l1UserTxs)
 		if err != nil {
-			return nil, tracerr.Wrap(err)
+			return nil, nil, tracerr.Wrap(err)
 		}
 	} else {
 		// 2b: only L2 txs
 		coordIdxs, auths, l1CoordTxs, poolL2Txs, discardedL2Txs, err =
 			p.txSelector.GetL2TxSelection(p.cfg.TxProcessorConfig)
 		if err != nil {
-			return nil, tracerr.Wrap(err)
+			return nil, nil, tracerr.Wrap(err)
 		}
-		l1UserTxsExtra = nil
+		l1UserTxs = nil
 	}
 
-	// If there are no txs to forge, no l1UserTxs in the open queue to
-	// freeze, and we haven't reached the ForgeNoTxsDelay, skip forging the
-	// batch.
-	if err = p.postForgeBatchCheck(slotCommitted, now, l1UserTxsExtra, l1CoordTxs, poolL2Txs, batchInfo); err != nil {
-		return nil, tracerr.Wrap(err)
+	if skip, reason, err := p.forgePolicySkipPostSelection(now,
+		l1UserTxs, l1CoordTxs, poolL2Txs, batchInfo); err != nil {
+		return nil, nil, tracerr.Wrap(err)
+	} else if skip {
+		if err := p.txSelector.Reset(batchInfo.BatchNum-1, false); err != nil {
+			return nil, nil, tracerr.Wrap(err)
+		}
+		return nil, &reason, tracerr.Wrap(err)
 	}
 
 	if batchInfo.L1Batch {
@@ -472,7 +551,7 @@ p.state.lastForgeL1TxsNum++
 	}
 
 	// 3.  Save metadata from TxSelector output for BatchNum
-	batchInfo.L1UserTxsExtra = l1UserTxsExtra
+	batchInfo.L1UserTxs = l1UserTxs
 	batchInfo.L1CoordTxs = l1CoordTxs
 	batchInfo.L1CoordinatorTxsAuths = auths
 	batchInfo.CoordIdxs = coordIdxs
@@ -480,10 +559,10 @@ batchInfo.VerifierIdx = p.cfg.VerifierIdx
 
 	if err := p.l2DB.StartForging(common.TxIDsFromPoolL2Txs(poolL2Txs),
 		batchInfo.BatchNum); err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 	if err := p.l2DB.UpdateTxsInfo(discardedL2Txs); err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 
 	// Invalidate transactions that become invalid because of
@@ -492,21 +571,21 @@ // (fromIdx, nonce) which already appears in the selected txs (includes
 	// all the nonces smaller than the current one)
 	err = p.l2DB.InvalidateOldNonces(idxsNonceFromPoolL2Txs(poolL2Txs), batchInfo.BatchNum)
 	if err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 
 	// 4. Call BatchBuilder with TxSelector output
 	configBatch := &batchbuilder.ConfigBatch{
 		TxProcessorConfig: p.cfg.TxProcessorConfig,
 	}
-	zkInputs, err := p.batchBuilder.BuildBatch(coordIdxs, configBatch, l1UserTxsExtra,
+	zkInputs, err := p.batchBuilder.BuildBatch(coordIdxs, configBatch, l1UserTxs,
 		l1CoordTxs, poolL2Txs)
 	if err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 	l2Txs, err := common.PoolL2TxsToL2Txs(poolL2Txs) // NOTE: This is a big uggly, find a better way
 	if err != nil {
-		return nil, tracerr.Wrap(err)
+		return nil, nil, tracerr.Wrap(err)
 	}
 	batchInfo.L2Txs = l2Txs
 
@@ -518,42 +597,7 @@ log.Infow("Pipeline: batch forged internally", "batch", batchInfo.BatchNum)
 
 	p.state.lastSlotForged = p.stats.Sync.Auction.CurrentSlot.SlotNum
 
-	return batchInfo, nil
-}
-
-// check if there is no txs to forge, no l1UserTxs in the open queue to freeze and we haven't reached the ForgeNoTxsDelay
-func (p *Pipeline) postForgeBatchCheck(slotCommitted bool, now time.Time, l1UserTxsExtra, l1CoordTxs []common.L1Tx,
-	poolL2Txs []common.PoolL2Tx, batchInfo *BatchInfo) error {
-	if slotCommitted && now.Sub(p.lastForgeTime) < p.cfg.ForgeNoTxsDelay {
-		noTxs := false
-		if len(l1UserTxsExtra) == 0 && len(l1CoordTxs) == 0 && len(poolL2Txs) == 0 {
-			if batchInfo.L1Batch {
-				// Query the number of unforged L1UserTxs
-				// (either in a open queue or in a frozen
-				// not-yet-forged queue).
-				count, err := p.historyDB.GetUnforgedL1UserTxsCount()
-				if err != nil {
-					return err
-				}
-				// If there are future L1UserTxs, we forge a
-				// batch to advance the queues to be able to
-				// forge the L1UserTxs in the future.
-				// Otherwise, skip.
-				if count == 0 {
-					noTxs = true
-				}
-			} else {
-				noTxs = true
-			}
-		}
-		if noTxs {
-			if err := p.txSelector.Reset(batchInfo.BatchNum-1, false); err != nil {
-				return err
-			}
-			return errForgeNoTxsBeforeDelay
-		}
-	}
-	return nil
+	return batchInfo, nil, nil
 }
 
 // waitServerProof gets the generated zkProof & sends it to the SmartContract
@@ -598,7 +642,7 @@ return &eth.RollupForgeBatchArgs{
 		NewLastIdx:            int64(zki.Metadata.NewLastIdxRaw),
 		NewStRoot:             zki.Metadata.NewStateRootRaw.BigInt(),
 		NewExitRoot:           zki.Metadata.NewExitRootRaw.BigInt(),
-		L1UserTxs:             batchInfo.L1UserTxsExtra,
+		L1UserTxs:             batchInfo.L1UserTxs,
 		L1CoordinatorTxs:      batchInfo.L1CoordTxs,
 		L1CoordinatorTxsAuths: batchInfo.L1CoordinatorTxsAuths,
 		L2TxsData:             batchInfo.L2Txs,

@@ -224,12 +224,12 @@ pipeline.batchBuilder.LocalStateDB().MT.Root())
 
 	batchNum++
 
-	batchInfo, err := pipeline.forgeBatch(batchNum)
+	batchInfo, _, err := pipeline.forgeBatch(batchNum)
 	require.NoError(t, err)
 	assert.Equal(t, 3, len(batchInfo.L2Txs))
 
 	batchNum++
-	batchInfo, err = pipeline.forgeBatch(batchNum)
+	batchInfo, _, err = pipeline.forgeBatch(batchNum)
 	require.NoError(t, err)
 	assert.Equal(t, 0, len(batchInfo.L2Txs))
 }

@@ -147,7 +147,7 @@ }
 	auth.Value = big.NewInt(0) // in wei
 
 	gasLimit := t.cfg.ForgeBatchGasCost.Fixed +
-		uint64(len(batchInfo.L1UserTxsExtra))*t.cfg.ForgeBatchGasCost.L1UserTx +
+		uint64(len(batchInfo.L1UserTxs))*t.cfg.ForgeBatchGasCost.L1UserTx +
 		uint64(len(batchInfo.L1CoordTxs))*t.cfg.ForgeBatchGasCost.L1CoordTx +
 		uint64(len(batchInfo.L2Txs))*t.cfg.ForgeBatchGasCost.L2Tx
 	auth.GasLimit = gasLimit

@@ -367,6 +367,7 @@ ForgeRetryInterval:      cfg.Coordinator.ForgeRetryInterval.Duration,
 				ForgeDelay:              cfg.Coordinator.ForgeDelay.Duration,
 				MustForgeAtSlotDeadline: cfg.Coordinator.MustForgeAtSlotDeadline,
 				IgnoreSlotCommitment:    cfg.Coordinator.IgnoreSlotCommitment,
+				ForgeOncePerSlotIfTxs:   cfg.Coordinator.ForgeOncePerSlotIfTxs,
 				ForgeNoTxsDelay:         cfg.Coordinator.ForgeNoTxsDelay.Duration,
 				SyncRetryInterval:       cfg.Coordinator.SyncRetryInterval.Duration,
 				PurgeByExtDelInterval:   cfg.Coordinator.PurgeByExtDelInterval.Duration,