Questions on recovery situations (not urgent)

Good day!

We have been learning more about postgres recovery, and I have come across
a couple questions that google has not satisfactorily answered for me.

1. pg_waldump refuses to dump a WAL saying "fatal: WAL segment size must be
a power of two between 1 MB and 1 GB", even though I have successfully used
the WALs for PITR. What's the magic trick to get around this fatal error? I
tried using a key unwrap function (same as in postgresql.conf) to no avail.

2. As I cannot dump the WALs, how do I determine the LSN or XID of a
transaction in the past?

3. When restoring forward, I have found recovery_target_time does not work
very well (maybe lack of granularity?), and recovery_target_lsn is better,
but pg_current_wal_lsn() only gives me the LSN *before* a transaction. Is
there a way to get the XID of a specific transaction?

4. How would I get the OID of a database and a table when the database is
down? I wish to map the filesystem names to database objects after a crash.
Is there a tool/app that can parse pg datafiles? I have to assume that if
there is not already one, it is not too hard to write such a tool if one
has experience with PG file headers and reading the opensource code.

Thanks for your time and attention!

--
Charles Schultz