So I tried to figure out the content of the wallet file, and a dump shows that each key value is prefixed with a non-printable mark, even when the data item is valid printable strings, what's the purpose of these markers bytes, like
etc.
$ db_dump -p wallet.dat
...
\07keymeta!\03\ff \15\06F0\97a\a4F\e2\15\01\b9;U%\97\d7\8c\0b\0b\e4`\bc\96\b2\ee@\db\8eL
\0a\00\00\00\ca3\91Z\00\00\00\00\0cm/0'/1'/461'j\11Z\e1t%\14\0d\13\0ai8\11^\8dz\e7bC\13
\07keymeta!\03\ff*r{\de5\e4/\a2_\f6+rIv\db(\92r\ee\dd\ce\18\daC\13\df\85\e3l6H
\0a\00\00\00\c93\91Z\00\00\00\00\0cm/0'/0'/254'j\11Z\e1t%\14\0d\13\0ai8\11^\8dz\e7bC\13
\07keymeta!\03\ffD9Y=\8e\0f\a51\95\ecs\98u\9a\da[A\82v\dd=\95\f9\bbf\a5\eby\18\0b9
\0a\00\00\00\ca3\91Z\00\00\00\00\0cm/0'/1'/594'j\11Z\e1t%\14\0d\13\0ai8\11^\8dz\e7bC\13
\07keymeta!\03\ffF\b3\c9\81\d4\1btNv\e9\ad\b3%\bbb\14\93\ff\e2}\9a\b4\dc\05\dc\b01\a5\87\ac^
\0a\00\00\00\c93\91Z\00\00\00\00\0cm/0'/0'/638'j\11Z\e1t%\14\0d\13\0ai8\11^\8dz\e7bC\13
\07keymeta!\03\ff\80A\e8\ea\c8*\92DU\e5W\fe\b3\e9]Vk2\b3\e4\fep\10\e4i\d5\1f\\\83\\3
\0a\00\00\00\cb3\91Z\00\00\00\00\0cm/0'/1'/921'j\11Z\e1t%\14\0d\13\0ai8\11^\8dz\e7bC\13
\07purpose"18V1UjWhRBEq7Kj3cXtLLjh2imd6UPWz9A
\07receive
\07purpose"1H1uEWBtsHe4tMzCRqGL6BkZBbu6xfnsmR
\07receive
\07purpose"32AvF5Vmnn9zD6VRf1D3vZXFHPuwdgEKqw
\07receive
\07purpose"35gnJvBQD424mgH9j2Udu6zoEsSXhzQkky
\07receive
\07purpose"3AMa4ZAh6R83sWRKsFvprpXvhzDuZ34yqm
\07receive
\07purpose"3M7vPcw9h6KaiRfpNNBRFC6mc918UaW6NF
\07receive
\07purpose*bc1qnfqmg4ty3qgft79gk3zgym3w3hqxmznxg9avup
\07receive
\07version
\ac\97\02\00
\09bestblock
\ac\97\02\00\00
\0aminversion
\9cp\02\00
...