Target to use about 25MB for the new layered txpool by default (#5974)

Signed-off-by: Fabio Di Fabio <fabio.difabio@consensys.net>

CHANGELOG.md

@@ -10,7 +10,8 @@
 
 ### Additions and Improvements
 - Add access to an immutable world view to start/end transaction hooks in the tracing API[#5836](https://github.com/hyperledger/besu/pull/5836)
-- Layered transaction pool implementation is now stable and enabled by default. If you want still to use the legacy implementation, use `--tx-pool=legacy` [#5772](https://github.com/hyperledger/besu)
+- Layered transaction pool implementation is now stable and enabled by default. If you want still to use the legacy implementation, use `--tx-pool=legacy`. 
+  By default, the new transaction pool is capped at using 25MB of memory, this limit can be raised using `--layered-tx-pool-layer-max-capacity` options  [#5772](https://github.com/hyperledger/besu)
 - Tune G1GC to reduce Besu memory footprint, and new `besu-untuned` start scripts to run without any specific G1GC flags [#5879](https://github.com/hyperledger/besu/pull/5879)
 - Reduce `engine_forkchoiceUpdatedV?` response time by asynchronously process block added events in the transaction pool [#5909](https://github.com/hyperledger/besu/pull/5909) 
 

ethereum/eth/src/main/java/org/hyperledger/besu/ethereum/eth/transactions/TransactionPoolConfiguration.java

@@ -64,7 +64,7 @@ public interface TransactionPoolConfiguration {
   boolean DEFAULT_ENABLE_SAVE_RESTORE = false;
 
   File DEFAULT_SAVE_FILE = new File(DEFAULT_SAVE_FILE_NAME);
-  long DEFAULT_PENDING_TRANSACTIONS_LAYER_MAX_CAPACITY_BYTES = 50_000_000L;
+  long DEFAULT_PENDING_TRANSACTIONS_LAYER_MAX_CAPACITY_BYTES = 12_500_000L;
   int DEFAULT_MAX_PRIORITIZED_TRANSACTIONS = 2000;
   int DEFAULT_MAX_FUTURE_BY_SENDER = 200;
   Implementation DEFAULT_TX_POOL_IMPLEMENTATION = Implementation.LAYERED;