txpool: don't validate block transactions if the pool is empty

Fix shall prevent from wasting the CPU during the major sync. Block
transaction don't need to be re-validated when the txpool is empty.

Fixes: #12903

client/transaction-pool/src/graph/pool.rs

@@ -271,14 +271,23 @@ impl<B: ChainApi> Pool<B> {
  // if it's not found in the pool query the runtime at parent block
  // to get validity info and tags that the extrinsic provides.
  None => {
- let validity = self
- .validated_pool
- .api()
- .validate_transaction(parent, TransactionSource::InBlock, extrinsic.clone())
- .await;
-
- if let Ok(Ok(validity)) = validity {
- future_tags.extend(validity.provides);
+ // Avoid validating block txs if the pool is empty (substrate/issues #12903)
+ if !self.validated_pool.status().is_empty() {
+ let validity = self
+ .validated_pool
+ .api()
+ .validate_transaction(
+ parent,
+ TransactionSource::InBlock,
+ extrinsic.clone(),
+ )
+ .await;
+
+ if let Ok(Ok(validity)) = validity {
+ future_tags.extend(validity.provides);
+ }
+ } else {
+ log::trace!( target: "txpool", "txpool is empty, skipping validation for block {:?}", at);
  }
  },
  }