Ann, your wording as always very clear.

> 3) Create a new lock series for blob garbage collection - oldest_blob
> for example.

As i understand this new lock series have the same meaning for
read-comited transactions as old lock series for snapshot transactions ?
If yes - may be it is better to name it using 'read-commited' words ?
Are we have symmetry here with snapshot\read-commited transactions
and new\old lock series ?

> 4) At startup, read-committed transactions also take a lock in the blob
> garbage collection series, identified by transaction id and containing
> the current oldest-active as the data portion.

What value snapshot transactions will put in this lock ? Zero ? Or its
will not take this lock at all ? If latter - why read-commited transactions
take usual transaction lock ?

Regards,
Vlad