The general online documentation is at:

http://docs.oracle.com/cd/E17076_04/html/index.html

but Bitcoin Core is using older version (4.8.30?)

http://www.oracle.com/technetwork/database/berkeleydb/downloads/index-082944.html

The entire older version is in the source archives: e.g.

http://download.oracle.com/berkeley-db/db-4.8.30.zip

I don't know the flags to the version of the BerkeleyDB included in your Linux distro. If it isn't exactly the same as your bitcoind then it isn't going to work until you rebuild all the db_* utilities with the exact same flags as used to build bitcoind.

One thing that you obviously missed is that you quoted an output from the "list of databases" inside "wallet.dat". The actual Bitcoin wallet is inside that file within a database named "main".

The other thing that you missed is that if you get all versions and build flags of BerkeleyDB right you will be able to monitor everything inside wallet.dat live, without shutting down bitcoind. That is the whole point of the exercise!

Edit: Oh, and I just noticed one more thing: it is about 5am in Ukraine. Did you actually sleep tonight? This isn't a 5 minute job that any zombie can do, you need to be really awake and conscious.

Edit2: In another past post you've mentioned that you are using the built-in account functionality. The "accounts" in Bitcoin Core never worked right. They are now officially depreciated. Nobody is going to fix any performance bugs in that code. You can't easily fix those bug yourselves because the "accounts" were designed wrong and fixing them would require major rewrite. The only people who ever used built-in accounts were fraudsters and people who have absolutely no understanding of accounting. I presume you were just completely unfamiliar with accounting and that was why you used them.