added configurable NuDB block size support in xahaud

cfg/xahaud-example.cfg

@@ -1127,6 +1127,40 @@
 #                           it must be defined with the same value in both
 #                           sections.
 #
+#   Optional keys for NuDB only:
+#
+#       nudb_block_size     Block size in bytes for NuDB storage.
+#                           Must be a power of 2 between 4096 and 32768.
+#                           Default is 4096.
+#
+#                           This parameter controls the fundamental storage unit
+#                           size for NuDB's internal data structures. The choice
+#                           of block size can significantly impact performance
+#                           depending on your storage hardware and filesystem:
+#
+#                           - 4096 bytes: Optimal for most standard SSDs and
+#                             traditional filesystems (ext4, NTFS, HFS+).
+#                             Provides good balance of performance and storage
+#                             efficiency. Recommended for most deployments.
+#
+#                           - 8192-16384 bytes: May improve performance on
+#                             high-end NVMe SSDs and copy-on-write filesystems
+#                             like ZFS or Btrfs that benefit from larger block
+#                             alignment. Can reduce metadata overhead for large
+#                             databases.
+#
+#                           - 32768 bytes (32K): Maximum supported block size
+#                             for high-performance scenarios with very fast
+#                             storage. May increase memory usage and reduce
+#                             efficiency for smaller databases.
+#
+#                           Note: This setting cannot be changed after database
+#                           creation without rebuilding the entire database.
+#                           Choose carefully based on your hardware and expected
+#                           database size.
+#
+#                           Example: nudb_block_size=4096
+#
 
 #       These keys modify the behavior of online_delete, and thus are only
 #       relevant if online_delete is defined and non-zero: